High kWh Usage in Efficiently Run Home
According to our utility provider, our usage during the winter months is more than 6000 kWh/month. I’m convinced this is insane, and I’m looking for confirmation that something is amiss.
I live in lower New York (Hudson Valley). I have a 1950s raised ranch of ~2000 sq ft. I have double-pane windows from ~2012. The attic has been air-sealed and has blown-in cellulose to R-50. I have a quality, variable speed ASHP (ducted, with all ducts within the envelope). T-stat is set to 68 degrees all day, no overnight setback. We have a new water heater (electric but not a heat pump). We have a wood-burning insert that we fire up on the really cold days, but otherwise, we don’t have another secondary heat source. We have the strip/aux heat in the air handler disabled. LED lightbulbs everywhere. We have a well pump (also new!) and no sump pump. It’s just my husband and I (no kids), and we have the typical gadgets of a modern home but nothing crazy — 1 TV, 2 laptops with monitors, 8-cup coffee maker… Run the washer/dryer twice a week. Turn off lights when we leave the room. You get the idea.
I’ve confirmed that the readings provided by my utility match my meter. Because the energy usage spikes in the colder months, I blame the ASHP. I intend to install Emporia Vue devices to identify the culprit — assuming that you all agree that something seems wrong.
Am I crazy? Or is this how much energy houses use these days?
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Replies
Feels on the high side. What is your design heat loss and design temperature? Also how many heating degree days in that month?
Could also be your unit is undercharged.
Unfortunately, we never did a Manual J, so I don't have good answers to your questions. I do want to go look at another thread where Dana gave some intel about using HDD. For the period with the 6,441 kWh (2/1-3/2), my utility suggests 924 HDD.
Unit could definitely be undercharged. We had the technician out a few months back to test it and it was fine, but worth giving it another look.
Say non heat pump electricity use is around 400kWh. That puts you at 6.5kWh/heating degree day. My guess is your heat pump is not running at all and all your heat is coming from the strip heater.
Easy check is to turn off the breakers for the strip heater, these are separate from the heat pump, and see if your system puts out any heat.
Unit charge is not the main problem as even if it was running at full tilt 24x7 you would not rack up 6000 kwh bill… heat strips running all the time or when the outdoor is running will do that though. My guess is the latter- whenever your ashp is running your strips run too.
That’s extremely high - can you post some of these bills? You can edit out everything besides start date, end date, and kwh. As many as you have is helpful! For reference - my coldest month heated with an ASHP only reached 1100 kWh. You’re in a colder climate, but it’s not 5x colder.
I have several spreadsheets looking at my usage over the past 2+ years, trying to analyze average daily rate, monthly rate, seasonal rates. So AMA! One thing that really throws a wrench into my calculations is that Central Hudson did a notoriously poor job of switching their billing systems in 2022, which means there are several months in a row where I only have estimated readings (not actuals). Then when they DID do an actual reading, the usage was MUCH higher than they expected, so it is a bit challenging to track usage against specific months/seasons due to that. Generally, though, warmer months seem perfectly reasonable (AFAIK) and then I get clobbered in the winter months.
Let’s see them! Note which months are estimated please
Hey Paul! In case you're curious, I've uploaded my electric utility summary here (it's through Central Hudson). As I mentioned before, there are some wonky bits where they were only doing estimated reads for months, and then sent a lot of bills in the fall of 2022 to catch up. I moved into the house in January 2021, so this captures everything since then. I included some notes in Column H (inc. when we installed the ASHP). I hope you get to see how fun it's been to deal with Central Hudson!
You are running 8.3 kWh all the time- 24 hours for 30 days. Assuming you have a 3 ton ashp running at full tilt all the time should be about 3.5- 4kwh (but they dont do that anyway)… Then you have another 4.3 kWh coming from somewhere else all the time. Get the Vue and investigate… something is very wrong with your electric consumption. It almost feels your heat strips are on all the time or you have a stalled motor somewhere.
Unfortunately I have a 5-ton ASHP. Yes, it's probably oversized, but no one would sell me a smaller one -- and no one was willing to do a Manual J to find out. Hopefully that doesn't alter the usage too dramatically. I'm estimating 4.4 kWh for the pump in prime wintertime.
I have definitely suspected that something is amiss with the heat strips, but then I feel like my house would feel much warmer than it is! The worst part about the high bills (other than the high bills) is that my house still feels cold.
Even a 5 ton running at full tilt all the time plus regular electrical use (fridge/washer/dryer/etc) will not result in 6 megawatts per month. There is something else festering there. As I mentioned I suspect heat strips running all the time or stalled motor somewhere. Get the Vue and start testing. You will find it- the extra consumption is huge.
6,000 kW/h per month is not "6 megawatts per month". "6 megawatts per month" doesn't even have any meaning, because the units are incorrect. I point this out because I see watt-hours and watts used interchangeably far too often, and then people draw incorrect conclusions. It's *very* important to be correct here. 6,000 kW/h would be equivalent to 6 MW/h, "6 megawatts" implies you are using 6 MW ALL the time. The PER HOUR part of the unit is VERY important.
6,000 kW/h per month is pretty high. A typical home around your size is going to be more in the 720 - 1,500 kW/h per month range or thereabouts, maybe double if you have very heavy loads. I suspect Akos is correct that your resistance heating is doing most of the "work" of heating your home. That doesn't mean your home will be warmer though -- it doesn't matter where the heat is coming from in terms of how warm the house is, so resistance heat won't make the house any warmer than the heat pump assuming the same setpoint on the thermostat. My guess is your resistance heat is set to come on at a slightly higher temperature than the heat pump, resulting in the heat pump never seeing things get cold enough to fire up in heating mode. You probably want to reverse that, so that the resistance heat fires up as a backup when the temperature in the home drops too far below the setpoint that the heat pump alone should be maintaining.
Bill
Yes- I meant megawatt hours. Skipped the “hour” word as it was obvious I was not talking about a nuclear reactor output. Ha
It's not W per hour, it's W times hours.
In reply to post #24:
It took me a bit to figure out what you meant, thinking I'd made a mistake somewhere, but I think you mean because of the convention I used (kW/h), read with the "/" like "divide", as in per-hour. It's a different convention to make the "hour" part stand out, and I agree it's not really correct math-wise. I think the reason that convention has sometimes been used is because the "/" character is less likely to get mangeled than some others. I have seen a dot used too (not sure what key combo gets that character), and also an "*", which would be more correct.
Bill
Bill, "Alt-7" creates a dot (assuming you're on a PC). For me, seeing the division symbol is more confusing in most cases than leaving the "h" off altogether.
Dropping the 'h' from kWh completely changes what it represents and can lead to very real misunderstandings of what's being talked about. Same could be said of the / symbol, but much less likely someone is meaning to refer to a 'rate of change of power per hour'. But the / symbol certainly confuses thing a bit as well.
Wikipedia has a section devoted to the 'watts per hour' misuse:
"Many compound units for various kinds of rates explicitly mention units of time to indicate a change over time. For example: miles per hour, kilometres per hour, dollars per hour. Power units, such as kW, already measure the rate of energy per unit time (kW=kJ/s). Kilowatt-hours are a product of power and time, not a rate of change of power with time."
BTU/h follows with the miles-per-hour logic. Another reason for confusion between kWh and BTU/h, one of which is an energy unit, the other of which is power.
Here's a question for ya:
Does dividing kWh by a unit of time reconvert the unit to power? Wikipedia claims it does. I'm having a hard time buying it. I suppose it would give you average power over that time-frame, but certainly not instantaneous power, which is really what I view power as being a discussion of.
from Wiki:
"Annualized power:
Electric energy production and consumption are sometimes reported on a yearly basis, in units such as megawatt-hours per year (MWh/yr) gigawatt-hours/year (GWh/yr) or terawatt-hours per year (TWh/yr). These units have dimensions of energy divided by time and thus are units of power. They can be converted to SI power units by dividing by the number of hours in a year, about 8766 h/yr.
Thus, 1 GWh/yr = 1 GWh/8766 h ≈ 114.08 kW."
Bill,
I'm sorry, but kw/h isn't a convention, it's simply wrong.
In reply to post #30, yes, dividing by unit time does do as Wikipedia claims, but there is a caveat...
If you use 4 kWh in a one hour period, than your load was 4kw over that hour. Easy. Now lets say you used 4 kWh in a 2 hour period. What was your load? was it 2kw for 2 hours? Was it 3kw for one hour, and 1kw for the other hour? Was it any of an infinite other combinations of time and power? As the time period over which you are averaging out your measurement increases, you lose detail as to exactly what you're measuring. I suppose this is a sort of inverse to the Heisenberg uncertainty principle, in that the less specific we are with our measurement the less we know about what was actually going on...
This is where the MWh/yr stuff can be misleading. Such measurements do NOT imply an average amount of power (load OR generation) over a year, they are simple total of ALL energy used (or produced) over a year. For all you know, ALL that energy was produced or consumed in a single day, with nothing the rest of the year (admittedly an extreme case, but trying to make a point).
That's one of the big problems with a lot of renewable energy sources: they are intermittent. Solar is obvious to everyone: not much is going on there at night. Wind is much less so. Just because a wind turbine is spinning, does not mean it is producing any given amount of power. Blade pitch can be controlled to maintain a constant speed of rotation at different wind speeds. What happens is that while the turbine appears to be, and is, spinning at the same speed regardless of wind speed, the amount of electrical energy being produced is much less at lower wind speeds. The result is that the AVERAGE output is not controllable, or particiularly predictable in many cases, which is where the issues come from. A conventional plant, for the most part, puts out rated capacity, or pretty close to it, the entire time it's running. If you need less, you can ramp it down. If you need to do maintenance, you can usually schedule things. With wind, you're at the mercy of the weather.
Bill
In response to post #32, I agree that mathematically it's not correct notation, because "/" means "divide", which isn't what a kilowatt hour is. It IS, rather unfortunately, sometimes used to emphasize the "hour" part, especially in anything that needs to use both kW and kWh. I do agree it's not really ideal, since it would be better if it were clear AND correct. Michaels "Alt-7" works • for • me, so that's a better way to go, and mathematically more correct, while also emphasing the "hr" part.
My point really is that there is a lot of confusion between what a kilowatt and a kilowatt-hour is, since they are very different (one is a rate, the other a quantity, like gallons per minute and just plain "gallons", respectively). I try to point that difference out on here when I see people use the terms incorrectly or interchangeably for two reasons: one is so that people can better understand things, but the other is because I often see the two terms used incorrectly intentionally to make things seem better (or worse) than they actually are. This is unfortunately most common in the media (probably usually by accident, because they don't understand the difference), but also by green energy people, which I consider a form of "greenwashing". No one can make good decisions based on intentionally misleading data, so it's important to try to use the units correctly. I do, also, see the irony in that statement after you pointed out that my use of the "/" character was technically incorrect in the unit we're discussing too :-)
Bill
Response to Bill #34
(And sorry for thread diversion)
Bill you say "This is where the MWh/yr stuff can be misleading. Such measurements do NOT imply an average amount of power"
It IS average power though, that's what 'average' means.
"If you use 4 kWh in a one hour period, than your load was 4kw over that hour."
This is not necessarily true, just like it's not necessarily true for the 2 hour period, or for the annual period. In all cases it's an average. Even so-called 'instantaneous' power measurements are a form of average (RMS) given the nature of AC, but that's a slightly different point, as the sinusoid is (in theory) predictable, whereas energy use over longer periods of time is not.
But your are right that the average power (especially when its over an entire year!) tells you nothing granular about the actual time when the power usage occurred. And that was why I was sort of having a hard time with Wiki calling it a 'power unit' even though technically they are right, it's average power.
It's the same as saying 'I traveled 800 miles in a day, so my average speed was 33.3 miles-per-hour.'
In resply to post #40, yes, I should I have probably used the word "constant" instead of "average" with the MW/hr of a year stuff, since that's what I'd really meant. The point was that those "over x long period of time" numbers don't mean you had a nice even and predictable flow of power at the same rate over the entire period, which is where people get misled. You can't count on some average wind power output over a year to produce the actual mathematical average amount of power implied over that entire period, because there are times it will produce a lot more, and other times it will produce a lot less, or even zero. The same does apply for even the one-hour time period I used in the example, it's just easier conceptualize if you draw the line somewhere and pretend it works out just to make the example easier to understand.
I suppose we could summarize all of this in that "the proper use of terminology is important", and "understanding the meaning of that terminology is important too".
Bill
That seems really high. We heat most of our house with a heat pump and run a steam humidifier, and our biggest month was about 3600kWh.
Thanks for the context!
I agree with Akos. I would get someone out to check the ASHP charge ASAP. Most companies offer "checkup" specials regularly.
Thank you, I agree. Last time the tech was out, he said everything was operating as intended. So I'm not too hopeful, but it's worth another shot. He also suggested that the 6000 kwh usage wasn't as high as others...
Get a different tech and different company.
6K is VERY high.
It could have something to do the HP - 5t is HUGE. How long ago was it installed? Was it installed before or after your air sealing & insulation upgrades?
Get the Emporia Vue because until you do it all ends up being speculation. That is the only way to get real data.
Did you also have a blower door test done with the air sealing & insulation upgrades? If so what was the result - it is a number expressed in x.x@ACH50. Post back with what x.x was.
It is also entirely possible your electric utility is having an issue. It happens. 20+ years ago I had a similar issue and fought with the power company for 2 months until they finally switched out the meter to shut me up and VOILA usage went down 5 fold or so....A power company that in 2023 does not do remote readings and only estimates usage during a billing system upgrade does not inspire confidence.
The ASHP was installed in Oct 2021 -- was previously running on fuel oil. The air-sealing and insulation was done in Dec 2021. So I didn't have a chance to check leakage post-insulation and pre-heat pump. To that end, I didn't bother to pay to have a blower door test done. The house is made of CMU, and I know some of the walls are poorly insulated, and I know it's leaky. I didn't see the point other than vanity in seeing a better blower door test result after doing my upgrades.
I have reached out to the utility to get a new meter. Apparently I'm on a waitlist, but they gave no estimate how long I'll be waiting. Incredibly frustrating.
The blower door does have a point.
In addition to the amount of power your home consumes, you wrote that you are always cold. That happens in a leaky house. The blower door would help you put this into perspective. If your house blows a 5ACH@50, that is not great, but it is an older house. If your house blows an 15 ACH@50, that will tell you your problem is air sealing so you can start to address it. I would get the test done...often with these tests they find surprising things.
Or get the energy monitor installed.
One of these two ought to be on your immediate to do list. Seems either would pay for itself in 1 month if you can cut your power bill in half...
Agree completely about the Vue or blower door test would pay for itself, assuming I can narrow down the problem.
I'd be curious to know the results of the blower door test for a greater context: Just HOW leaky is my house? But again, I'm not sure much more can be done to prevent the leakage at this stage -- other than taking down drywall and adding insulation in the framing/furring strips. I've already had a consult to see about adding rigid foam insulation on the exterior of the house (with siding), and it was exorbitantly expensive ($60K+).
I'm in central Washington state, 2.5 ton ASHP, HP water heater, everything is electric (no natural gas in our town). My highest monthly in the last couple years was 1600 kwh. House is about 1700 sq ft, in the process of being remodeled (so there's exterior insulation, but the windows are not permanently installed, and thus leaky).
I'm surprised to hear that you have heat strips disabled, your ASHP produces enough heat when it gets really cold? Mine definitely uses heat strips when it's cold.
I think it helps that my ASHP is 5-ton, so even if it's operating at poor efficiency, I'm still getting some BTUs in. The house has certainly been livable, but I would not describe it as comfortable. We've had a mild winter, and my husband still wore long underwear every day under his jeans. I'm much more vain, so I just chattered throughout my video calls. :)
Yeah, I'm in the long underwear camp, and our house is usually 62-64F. . .
If this was me I'd start by taking notes on electrical use at the meter for a few days. I'd take a photo of the meter reading every 4 hours or so during the day and in the morning, and then the next day I'd turn the thermostat way down and see if the power use drops way off. What's your summer electric use? Mine is in the neighborhood of 400 kwh, if yours is close that means that 93% of your use should be heating.
Seems pretty insane to me also....We're on Martha's Vineyard, so definitely not as cold as Hudson Valley, But our home is about 2,500 square feet....We have a 15 year old Sanyo 3-ton multi-zone unit plus (3) ductless 6,000 butu units in a new extension. We ran about 3,500 kWh in our coldest month.
Have you checked the duct and filters? Equipment may be working but the warm air may not be circulating properly.
I've checked the filters; we clean/replace them regularly. I haven't had a good way to check the ducts. If I get my electrical bills lowered, I'll use the savings to get a scoping camera for the ducts -- haha. I would not be shocked if there was a duct or two that was partially cut off; I know as a whole they're undersized and better suited for an oil furnace.
You have a delivery problem. How much undersized are the ducts? Is the fan speed correct. All that heat is going somewhere. Are you just heating the sheet metal and not the house? If the supply or return ducts are not size properly, your house will not get warm and the system could run at full speed all the time.
I had high bills for a few years and eventually traced it to a leaky toilet causing the well pump to run a lot.
Agreed, that seems a possible candidate. A leaking hot faucet would make it even worse.
This is definitely an interesting theory! If I get the electrical monitors, I'll be able to narrow down if it's the ASHP or the well pump. Well pump is my backup culprit if the ASHP turns out to behaving itself.
Seems crazy to me. Our 2500 square foot, all-electrical house peaks at about 1200kWh per month. That's in a similar (slightly colder, if anything) climate, standard electric water heater and a ton of cooking and baking.
Having a good energy monitor seemed kind of frivolous at the time I bought it, but it's helped diagnose a couple of heat pump issues and provided a lot of other issues. Might be worth installing. If you end up fighting your utility provider, you'll need something more than your personal conviction that you're being over billed. Brultech is the brand I went with and have been pleased with it.
We have about 1650 square feet of conditioned space in Maine. Pretty Good House, well insulated and airtight. All electric, hot tub, 2 minisplits, house is kept at 72°, electric resistance water heat (just replaced with HPWH). In eight years, our worst month was about 1500 kwh. 6000 is horrifying.
Have someone watch the electric meter spinning while somebody else starts turning off circuit breakers one at a time. When the meter slows down considerably, you'll have pinned down the culprit circuit in 10 minutes, for free, and at least have a better idea where all this electricity is going.
If nothing jumps out at you, try it at different times of day of during colder weather. Easy and simple. 6000kWh is nuts.
Who has mechanical/analogue meters anymore? I haven't seen one in about 30 years.
I do! On the waitlist for a new, ERT meter from the utility, but it could still be years.
We live in Maine and have an Emporia Vue monitor in each of three buildings we own. My wife and I live in a 1,200 SF apartment that sits over a 3-car garage (one of those buildings). Open floor plan except for the BR and bathroom, but 13 foot cathedral ceiling. It was built 10 years ago with 2x6 construction and blown-in cellulose insulation, with decent quality double-pane windows. So, nothing spectacular - just decent. The garage below is kept at 45 (propane heat for it, that comes on only rarely, with insulation and air sealing between garage and apartment). We keep our Daikin ASHP set to 70 all winter in the apartment. The ASHP draws about 650 KWH/month Dec-Feb (the Vue overall aligns almost perfectly with the utility company meter). Based on that and the information you are providing, I'd say you really need to find a different HVAC company to evaluate this situation. There's just no way you should be using anything remotely close to that much energy to heat a 2,000 SF ranch house.
Are the strip heaters a different breaker? Or at the least do they have separate wiring at some point that is accessible?
An alternative to messing around with an energy monitor (best) would be to get a cheap amp clamp meter in order to at least get a snapshot of what's going on.
https://www.amazon.com/Etekcity-Multimeter-MSR-C600-Auto-Ranging-Multimeters/dp/B00NWGZ4XC/ref=zg_bs_5011680011_sccl_7/130-3068001-7726524?psc=1
Much cheaper but also a lot less time invested vs installing an energy monitor (I just installed one and it takes a bit of time, especially if you have a messy panel).
You could contact either and electrician or energy auditor who is comfortable testing inside electrical service panels. I perform a lot of this type of testing and usually can find the problem within a few minutes if the issue is presenting during the time I'm in the panel. I found a similar issue a few days ago in an older home, there was an electric heater in a crawlspace no one knew about. It was causing a $200 per month spike in the owner's electric bill. I don't recommend this type of testing without training and experience working in live panels.
Thank you, Randy. I appreciate the guidance about getting a trained professional for this. It's tempting to try it ourselves, but I'm personally not thrilled with the idea of playing around in the panel myself.
Just turn off the breakers one at a time like I said in post #36. Completely safe.
You should get a clamp meter ($15 at Harbor Freight.com) to put around the wires going to your heat pump to check the current draw. Also, what model of heat pump do you have? Maybe you have a warranty claim. And do you have insulation and air sealing done in your basement, rim joists, etc.?
The heat pump is an American Standard Platinum 18 (5-ton). Should still be under warranty if we were able to identify the issue. Knowing what I know how, I wish I had gotten 2x smaller ASHP and zoned the house into upper/lower levels. Or gone geothermal, but I still suspect that would have introduced different issues.
Air-sealing was done on the rim joists. No basement; just a partially submerged lower level (all conditioned).
5 ton is a lot. I had the same problem, that the installers said I needed a 62000 BTU. I ended up installing a 30000 Mitsubishi BTU heat pump using the ductwork from the old 120,000 btu gas furnace. In retrospect, this is not very efficient because the oversized ductwork ends up containing pockets of cool air between cycles. So I am going to remove a couple of registers and eliminate 60% of the basement ductwork, thus increasing the air flow in the other ducts that feed the first floor.
We now have 18000 btu ductless on the first floor and 30000 btu in our central unit, but I still think the 30K will be more than needed when we are all done! That's because we did a major overhall of the walls of the first floor, which were older than floor 2. We are just finishing the installation of exterior insulation, averaging 2.5" of foam, air sealing the entire envelope. I put in a link to this below.
BTW do you know how many gallons of oil your house was using before the heat pump went it? In my house I provided people here with our gas usage which helped us judge what size heat pump to get.
https://www.greenbuildingadvisor.com/question/update-2-on-1930-house-in-northern-ma-adding-many-kinds-of-exterior-insulation-all-at-the-same-time
Rich, unfortunately I don't have a good gauge of the oil usage. I wish I did. I bought the house in Jan 2021, and installed the ASHP in Oct 2021. So I never had a full winter with the oil furnace, and there was an undetermined amount of oil in the tank when we moved in.
Start with confirming the kwh (notice I used an h and didn't use a slash) of the incoming mains to the meter with a clamp on amp meter as per post #13.
If that checks out then start diagnosing individual circuits.
This is specialized and potentially life threatening work, so consider asking an electrician to come out if you don't know what you're doing. An electrician may be cheaper and faster than the energy monitor, but up to you to price it out.
Also, there is the Sense monitor, I believe it's way easier to install, but I can't speak on it's accuracy as it works on a different principal.
Jamie
Despite going out of your way to point out you included the 'h' I'm genuinely confused. Post #13 mentions using an emporia vue. That would be in accordance with taking energy measurements (h included as you say). But then you mention a clamp on amp meter, which typically describes devices like those talked about in post 38, 39, and 42, which would give amperage--and multiplied by voltage could give you wattage (power), not watt-hours (energy).
Are you referring to the emporia vue as the clamp on amp meter?
If all you're looking for is a "wow, that's not what I was expecting!" kind of result, it doesn't really matter how accurate or reliable your clamp meter is. You won't get super reliable watt readings with a clamp-on amp meter and manually calculating wattage from a voltage reading, but you can find circuits that are using a lot more than you thought they were.
I read that post #43 as a sort of "go looking for things using lots more power than you'd expect", in which case precise measurements aren't very important. I've sometimes done this if I think something is "on" somewhere that shouldn't be, in which case a clamp meter showing amps alone is a quick way to find the loaded circuit.
Bill
Bill,
My question was why did Jamie use kWh if he was referring to an amp clamp meter. Nothing to do with accuracy. But perhaps they were indeed referring to an energy monitor and just calling it a 'clamp on amp meter.'
I don't see why a clamp meter wouldn't be fairly accurate other than not accounting for reactive power (which in the case of resistance strips is a non issue). I'm sure some clamp meters are more accurate than others though...
I've seen people use clamp meters to get an amp reading, then multiply that by whatever they saw for voltage and call that "watts". That might get you close in some cases, but it's not an accurate way to measure wattage.
You would need a true RMS clamp meter for any kind of wonky load. I've just found myself that a lot of the cheaper clamp meters tend to not be very accurate, especially at lower current levels. If it's a good meter, it should be pretty close. I've just seen so many people using "meters" of very questionably accuracy and reliability that they've bought through places like Ebay and Amazon. Many of those are very inaccurate, and measurements made from them can result in incorrect conclusions when trying to diagnose strange problems. That's not to say that is the case in this particular instance, but I'm always suspect these days.
Bill
6000 kWh is a huge amount. I have a 3000 square foot house built in 1860 (some air sealing and insulation work but very leaky) and we are between 2000-3000 a month even while heating with 84k btu of ducted heat pumps.
I would definitely speak to an electrician about measuring consumption and/or putting monitors in. then speak with a the manufacturer and a new HVAC tech if your drawing too much from the units.
So many of you were engaged with this post, so you deserve an update. Thanks to you, I was able to ascertain that yes, my energy usage was very high and indicative of a problem. The good news is that we were able to determine quite quickly that the ASHP was the culprit. We had some warm days recently that allowed me to shut down the HVAC system, and by keeping daily meter readings, it was obvious that the HVAC was causing the draw. Tech came out, and quickly determined that the aux strip heat was running any time that the system was on. (This irritated me immensely, as I had requested and had been told that they had been locked out.) Akos and Greenright are our winners! Turns out, that anytime we have a power outage and the system resets, the default is to run the aux strip heat. Unfortunately for me, I live in the woods and 1-sec power outages are frequent.
Techs left, and we thought that was that. Surprise! We discovered the ASHP was not working as expected when we had a couple warm days, and even with the heat on, the house remained significantly cooler than the outdoor air temp. In fact, the interior air temperatures continued to drop. I decided to turn off the system completely -- and it made no change to the temperature whatsoever. The techs came back, and lo and behold, the entire compressor is failing on my 1.5-yr-old ASHP. They're going to replace it, but I have concerns about the same problem happening again. It seems obvious to me that the system is oversized and it is working far harder than it should be, causing it to fail. Their solution is to add a bypass damper in my ductwork to cut down on the static pressure... I know this isn't the proper solve to the solution, and after doing some additional research, I've decided I'm not letting them anywhere near my ductwork without a second opinion.
On the bright side: I installed the Emporia Vue monitors. They've only been in for 1 day, so no major learnings yet, but I'm looking forward to playing with that data. I see some new lightbulbs in my future.
Thank you for the follow up. Your usage wasn’t high enough for the strips to be on all the time, but was just about right for them to be on when the ashp was running- hence my guess in my previous post. Glad you figured it out
On your compressor issues- short power outages (couple seconds) will kill anything. You need to look into power- conditioning means / safety devices. An early compressor failure is not common when power is of good quality.
On your system being oversized so it is working harder so they will reduce static pressure- this makes zero sense and is wrong on so many levels I am not going to comment on it. Look for another contractor.
>"On your compressor issues- short power outages (couple seconds) will kill anything. You need to look into power- conditioning means / safety devices. An early compressor failure is not common when power is of good quality."
I'm going to have to disagree with this slightly. Brief power interruptions aren't usually much of a problem, unless they are VERY frequent. What is much more of an issue is if those "brief outages" also involve other things, especially longer periods of low (under) voltage. Low voltage "brownout" conditions CAN cause problems. Your Vue monitors can probably look for this kind of issue though. I would not worry too much about fancy power conditioning for the heat pump, although I do recommend a "whole home" transient voltage suppressor (a "surge protector") be installed on the main panel. I like the little Ditek devices for this, which are easy to install, and under $100, but there are many other manufacturers making similar products. I would recommend not buying no-name brands though, especially from questionable import sources, since there can be some fire risk from these under certain conditions.
Short cycling WILL damage a compressor, and if your system is significantly oversized, you may have been having an issue like that. I don't see a bypass damper as being the correct fix though, you really need a "right sized" unit, not something to artificially reduce the capacity of a too-big unit.
Bill
Bill, the brief interruptions themselves are not the problem. The problem is the over/under voltage spike when the power comes back on. Those spikes is what kills motor windings let alone pcbs. This is pretty textbook so I am surprised you disagree…
PCBs aren't "killed" by power interruptions. If this were the case, anything electronic with a power switch would soon die. The same goes for motor windings, for the same reason. Not *all* power interruptions come with under/over voltage transient events. Some do, but not all.
Typical short-duration utility power interruptions are usually due to switching actions within the utility's system, such as switching circuits in a substation to a different transformer. There are also tap changers, to adjust voltage throughout the day. It's actually pretty common to have some amount of switching a little before the start of the workday, and again in the early evening, as these kinds of switching events are usually related to changes in system loading. You don't normally see undervoltage transients from this sort of switching, and any overvoltage transients, if any are present at all, tend to by minimal.
Interruptions associated with things liked downed lines, and sometimes other kinds of failed/failing equipment, are more likely to cause line voltage transients, but these type of events are fortunately much less frequent. The utility system has protection built-in for the normal kinds of switching that is done, so it's mostly the unexpected type issues that you need your own protection for. Normal line voltage transients are not usually high enough to damage motor windings, electronic stuff is considered to be more "sensitive". A whole-home TVSS device will easily handle any of these types of overvoltage transients that are of short duration and relatively low energy levels (i.e. not lightning, which tends to be something the protectors can save you from only once).
Brief undervoltage events of a few cycles or so as you'd see from load switching won't damage motors, and won't damage electronic devices. Undervoltage can make electronics unreliable, but tends to only cause damage for if the undervolage event is sustained over a relatively long period of at least few minutes (although this depends on the load).
The "textbook" part is because if you switch an inductive load into an open circuit, you get transients EVERY TIME. The utility system is NOT an open circuit though, so most of those transients are effectively damped by a combination of the protective devices already in the system (there is typically a TVSS device on the primary side of every distribution transformer and every aerial-to-underground cable transition in the system), and also by the loads.
Bill
Bill, nothing gets killed by power interruption- correct. But it does when power comes back on as under/ over voltage spike. Especially if power has been off for short periods of time- like seconds.
I have dealt with countless equipment outcomes of such power interruptions.
Since they will need to replace the compressor, now is the chance to get the sizing right.
Run through Dana's article using the energy use in the cold months when it was running with the strip heat (subtract your non heat kWh usage from that month to get heat use, kWh/29.3=Therms for the calculation, strip heat is 100% efficient so all the energy goes to heat).
In most cases, a smaller outdoor unit can be used with the larger indoor unit and as a bonus you get some extra efficiency out of the setup.
The one thing that you do not want is a bypass damper. This does not work on heat pumps, will only cause energy use to go up and can sometimes cause the compressor to fail.
https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler
THANK YOU for the update. Some good advice below regarding a solution, which is not the one your HVAC contractor recommended. If your HVAC contractor is not willing to replace the outdoor unit with a smaller one at their cost, you can perhaps offer to let them reimburse you for the insane amount of electricity used for x months, and then just hire a different, competent contractor. The advice below to call the mfg rep it spot on.
Just curious: Did you end up installing the Emporia Vue yourself, or did you hire it out? If you hired it out, do you mind sharing what they charged to install it?
Thank you for updating us!
I'm glad you solved the electricity problem.
I'm sorry you now found another problem!
I think you're right to move on from the current HVAC contractor. Because what you're writing/being told is the issue and the solution isn't necessarily making sense. I suggest calling the technical rep of the brand of your equipment. Maybe they'll come out to take a look and you might get some new insight. And specifically ask that person for a recommended contractor.
Jamie
Bill, do you think about the internal short cycle prevention timers built in to seemingly every digital thermostat is enough protection?
If the unit was trying to operate on voltage 20% less than normal for hours maybe you could damage the compressor but its thermal overload should protect it.
Are they replacing just the compressor itself or are they replacing the entire outdoor unit?
The quality of service Katie has received make me distrust the diagnoses of a bad compressor.
I also doubt that this statement is true. “Turns out, that anytime we have a power outage and the system resets, the default is to run the aux strip heat.” If this were true the system would forget every setting and what function it was set to preform with every power interruption and no one would except such a system.
My opinion oversizing is not the root of the failure.
My guess is the manufacture is unlikely to replace the entire outdoor unit under warranty for any reason and tend to be very skeptical about compressor failures as they tend to be very rare.
Walta
Short cycle timers in thermostats won't help if the compressor is tripping out on overpressure. It depends on what is going on. If the compressor itself is tripping out, you'll hear it run, gradually change in pitch as it's running, then a CLICK and it will trip out. At some point it will reset and continue the cycle, unless it locks out when it trips out. This is usually easy to figure out when you have the system in front of you, not so easy to do in an online forum :-)
Prolonged periods of undervoltage are a problem, and you don't always have protection (or at least, not sufficient levels of protection) to protect against problems. In the commerical world, it is common to use "phase monitors", which often watch for low and high voltage conditions too, to lock out motors when the utility power gets excessively wonky. It is unusual for residential power to get so bad as to cause these kinds of problems, but it's no unheard of. I would keep an eye on the historical data from the Vue monitors to see if that information can provide any insight in the nature of potential problems that may be impacting the equipment here.
I do think you have a point about the service work that's been done though. It would probably be adviseable here to seek out a different contractor to get a second opinion, and ideally get a contractor that is familiar with the type of system you have installed.
Bill
If you can find out who was your heating oil provider before you moved in, you may be able to access 1 year's worth of oil usage history. That would give you an idea whether your envelope needs some work or not. You probably should downsize to 3 ton, however I think you need to be really sure that your insulation and ductwork are both in good shape, meaning free of gaps and holes. So maybe get a different HVAC person to evaluate whether the duct work follows best practices and also measure the temperatures you are getting at all the registers. Also a thermal camera can help detect places on the wall or floor that are cold spots.
In my house the original 2010 ductwork was leaking half of the heat into an unconditioned attic. We sealed up the attic with spray foam on the roof deck, fixing part of the problem. Four years later we decided to throw away all the flex duct and replace it with hard duct. Flex duct was used for long runs which was not correct. The contractor also found holes in the existing metal duct main supply duct and inadequate return air. So almost everything was replaced. Two years after that I checked the air handler. It still had a ton of leakage in back of the original main trunk despite $5000 we paid the ductwork company in 2014. I ended up buying duct sealant and fixing that issue.
Also in my house -- this is in 2022 -- we had areas of the perimiter of the 1st floor that measured around 40 degrees on the thermal camera when it was 20 degrees outside. We fixed this with exterior insulation, covering all the way down to the bottom of the sill. After some of our insulation work it quickly warmed to 55 degrees on those cold days and I bet it's much better today although I can't measure it until next winter.
Ductwork can be an issue with the "smart" heat pumps, because the heat pump controller expects the temperature to gradually increase. But you could have a warm duct too close to the thermostat, or duct that hits a cold spot in your house entirely failing to warm the room with the thermostat when the heat goes on. Just a few weeks ago I had to move my thermostat to get it away from a cold zone (top of stairwell). I would not be surprised if some of these heat pump systems are programmed to assume the that home they are installed in is well insulated. Unfortunately a lot of homes that have bad insulation are getting heat pumps nowadays, thanks to all the incentives and tax rebates out there.