Water heater decisions
In the process of building a new house and trying to decide on the best strategy for hot water heating.
We tried to be efficient with our floor plan design, and were able to clump the bathrooms and laundry room in one corner of the 2nd floor of our house. The guest bath is downstairs, almost directly underneath the baths upstairs. The only outlier is the kitchen and a half bath, which is on the other side of the house.
The house is all electric, and there are a couple of things I’m concerned about…
First
The traditional placement of a hot water heater is in the basement (if you have one), but I am concerned about the long run from the heater to the 2nd floor. I am also concerned about the long run to the kitchen and half bath.
One solution to this would be to locate the heater in the upstairs laundry room, which would mean that the hot water run would only be a few feet to all the fixtures upstairs, and just a one-story run to the guest bath below. The concern here would obviously be having a water tank on the 2nd floor, and the risk of water damage if something leaks. However, there is already some risk involved with this in the laundry room already, and I wonder if I can include some waterproofing features into this room to help lessen the damage if something happened. This doesn’t solve the problem of having a long run to the kitchen, but I wonder if that should be solved by a separate heater just for those fixtures, placed directly under the kitchen.
Second
I am concerned about recovery times for electric water heaters. We have a family of four, and pretty soon we are going to have 4 showers going in a short period of time. We have always had gas heaters, which have a quicker recovery time, and the kids are younger now so they normally bathe at night, but in a few years they are going to be showering in the morning like everyone else.
A possible solution to this would be a tankless heater. In addition to the efficiency, the advantages of a tankless heater would be that I could place it in the upstairs laundry without worry of a tank leaking and causing damage. However, I worry about it being able to keep up with the demand. I would imagine there will be times when two showers are running at the same time, and I’d worry that the heater couldn’t keep up with demand. I know that an electric tankless heater is a different animal than a gas tankless, in terms of output. I have done some reading on GBA and other sites and it looks like the jury is still out on these devices, or at least they were a few years ago when those articles were written. I’ve also wondered if adding a small tank between the heater and the fixtures would be a fix to some of the drawbacks to tankless (the “cold water sandwich” and problems with low flow not triggering the heater), but then you are also adding the back the drawbacks of tank-type heaters. Plus, you’d have the expense of both installations.
And then a third thought I had was a HPWH in the basement. This would not solve any of the problems above, but I would like to have wide plank hardwood flooring but have been warned about cupping due to the moisture from the basement. This is a little off topic, but I wonder if the HPWH would do enough de-humidifying in the basement to help in this regard. Or, would a couple of dehumidifiers be better? Or, would neither of those do enough to prevent the cupping?
Sorry this post is so long, but there is a lot to consider.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
I will offer this , A tankless and tank type water heater will leak the same amount with the exact same size hole . The amount of water will be based on system pressure , not the amount of water in a tank . When a leak happens in a system with all faucets closed it matters not whether the heater has a tank or not . Ask anybody who has tried to replace a tank type and could not solder the new connections because water remained above in the piping .
Wow, this is an amazing post!
If you plan ahead for leaks, you can make your upstairs utility room a better place to have a leak than a basement--an EPDM membrane to make the whole floor a drain pan, and/or drain pans for each appliance including the water heater. Do make sure you are structurally ready for the weight of a big tank.
On the other hand, basement dehumidification is a good benefit of a heat pump water heater. And given your thoughtful compact layout, the energy and convenience disadvantages will be minimal, at least if you can convince your plumber to run minimum-size hot water pipes so that they don't have excessive volume that you need to heat.
In any case, I strongly recommend against electric tankless, except perhaps for a small handwashing sink somewhere. The peak electric demand is crazy high, and you'll pay now for the higher-capacity electric service that requires, and you'll likely pay later if utilities start putting peak demand charges on residential bills. You'll also know that you are a troublemaker for the grid, contributing more to requiring the utility to build more peak capacity than other customers do.
A great way to mitigate the recovery time issue with many showers happening at once is to add a drainwater heat recovery system: http://www.renewability.com/power_pipe/index.html
That works really well with showers, and even better when the showers happen around the same time, either simultaneous or sequential. It will help your recovery time and lower your overall water heating energy use. Well worth it for a situation like yours.
If you have bad enough basement moisture to have your floor cup, you've probably got a moldy disaster in the basement. You should be planning to avoid basement moisture problems--there are some good articles here about that. It is still a good idea to dehumidify the basement, but if you don't have moisture sources the dehumidifier won't run much--the heat pump water heater might do plenty without anything else.
Water heater failure is rarely sudden and catastrophic. Our is in a 2nd floor hallway sitting inside it's own drain pan that is similar to one in which you place your laundry machine. We replaced it at year 12 just out of an abundance of caution.
Just drain a couple of gallons out the bottom via lower drain valve 2x year to remove any sediment.
Thanks for the replies. Yeah, I had thought about putting a drain in the middle of the laundry room floor for insurance. With the shower close by I could tie the laundry to the shower drain so I wouldn't have to worry about a trap.
Thanks for the suggestion on a heat recovery system. I'll look into that.
Regarding the hardwood cupping issue... I don't know all the details, but I don't think a basement has to be very humid to cause the cupping, it just has to be more humid than the rest of the house. I haven't researched how much difference is needed to cause cupping, but I believe you can have an acceptably dry basement but if the humidity is higher than the rest of the house, you can get cupping, especially in wider planks. Then again, I guess the opposite is true. If the basement is drier than the rest of the house, the planks would curl in the other direction. Hmm...
If you tie it into the standpipe from the shower above the trap you run the added risk of water backing up there in the event of a drain blockage . A check valve would help in that type of circumstances .
Regarding your question #2, where I live in Minnesota we have "Off Peak" water heating. The water heater heats water from midnight until 7 AM (at a reduced rate). I have had this system for about 25 years in 3 different houses and have very rarely run out of hot water, including a time with 2 teenagers in the house (one being a girl who liked 45 minute showers) and 2 adults. We use a 100 gallon water heater and also mix a little cold with the hot water with a mixing valve. The only time we ran out of hot water was if my kids had friends over, everyone took a shower and my wife washed 4-5 loads of clothes and ran the dishwasher.
Hey Charlie, I assume the hot water recovery system is best used when the water heater is close to the drain pipe? I don't guess the heater has to be located underneath the system, but could be located above the drain?
Yes, the drainwater heat recovery system is best with a compact layout. But the proximity of the "powerpipe" heat exchanger to the water heater is not critical. The water coming out of there is only luke warm, so it doesn't lose as much heat as the hot water pipe coming out of the water heater. So from that perspective, you'd do better with the water heater upstairs, making the hot pipe a little shorter and the "luke-warm" pipes longer. But it's fine either way, especially if you insulate the pipes.
Most of the benefit is that it gets the cold water coming in at ground temperature up to room temperature before it goes into the water heater. If it gets it above room temperature, that's a bonus.
Regarding running water to the second floor from the basement - the hot water usually comes out of the top of the water heater, ~6 feet up, then runs to fixtures about ~4 feet off the floor. Going straight up from the basement water heater to the second floor is only a 20 foot run. I get annoyed by the 45 second wait time for hot water in my kitchen (one of these days I'll run a smaller line for it), but my second floor master bath has perfectly reasonable waits.
Charlie, thanks for the response. I don't know how much it costs, but I like the powerpipe idea. If the heater is upstairs, the water line has to go up the same cavity as the drain anyway, so you might as well wrap it around the drainpipe and capture some of that heat as it passes by. Sounds like a no-brainer... depending on the cost, obviously.
Would you run 2 water lines up to the 2nd floor (one for powerpipe and one for the cold water), or would you just run one water line up and then split it after the powerpipe? Seems like it would be more efficient to just run one line. But I guess that would affect the cold water too much. It would be a normal temperature when the shower wasn't running, but when the shower was on, the cold water would be lukewarm. We might be OK with lukewarm water at the sinks, but I guess that may make adjusting the shower temperature difficult if the cold water starts cold but then gradually gets warmer. You'd have to constantly adjust the hot/cold mix.
Thanks Tim C. That's a good point. I may be a overthinking it a little. I grew up in a 2 story house where the heater was in the basement on the other side of the house. You could usually start the shower and then take a nap on the bathroom floor while you waited for the water to heat up. Since then I've lived in single story houses with the heaters closer, but still probably longer than the 20 ft range. The basement of this house is wide open and will be unfinished, so I can place the heater anywhere. Putting it directly under the bathrooms means it only has to travel 20 ft or so, as you say. Probably not that long of a distance in the grand scheme of things.
Hmm...decisions decisions.
There are two things you can do with the water that is warmed by the drain water. You can have it go into the hot water heater inlet, reducing the amount that the water heater needs to raise the temperature. If the distances make that difficult, you can have it go to the cold water side of the shower so that you end up using more cold and less hot to get the same shower temperature. Or you can do both, which reduces hot water energy use the most. Sending it to another faucet where you might actually want the water to be cold would be a bad idea.
Thanks for the reply Reid. Why would it be a bad idea to run lukewarm water to the other fixtures? Just from the standpoint of wanting colder water than it would provide? Or is there some other reason I'm not thinking of? Keep in mind that this will just be the cold water line to the 2nd floor. There would only be showers, toilets, lav faucets and a clothes washer. I don't think the lavs would be affected at all...maybe our tooth-brushing water is a little warmer than normal if someone is showering, but that's it. The late night cup of water would still be cold since there wouldn't be a shower running at that time. The toilets may waste a little warm water if there was a flush during a shower, I guess.
The reason I was thinking about running the entire 2nd floor cold water supply through the recovery system would be simplicity and cost. That would one less water line to run to the upstairs. I don't know the cost involved in running a second line, so it may be not enough to worry with.
The only concern I would have in running the shower's cold water supply through recovery system would be whether or not that would make setting a comfortable shower temperature difficult, at least for the first user. For example, when you first get in the shower, the cold water is cold and the hot water is hot. So, you set a comfortable mix of hot and cold water to get to the desired temp. However, as the warm water that runs down the drains starts to warm up the cold water, the water coming from the shower head gets too hot for comfort, so you have to adjust the mix colder. Either that, or you set the valve to a colder mix than comfortable and then wait until the water warms up. But since it is colder coming down the drain, the cold water isn't as hot, so you have to turn it a little hotter. But then it warms up the cold water and you have to turn the water colder. I guess they have shower valves that automatically adjust the water mixture for you?
Am I overthinking this?
What about the heater for the other side of the house, where there is just a kitchen faucet, dishwasher, and lav faucet? Would an elec tankless work for that or would a small tank be best?
The output of a 50% efficiency drainwater heat exchanger is not really lukewarm- it's downright tepid, room temperature or slightly above when flowing at 2.5gpm. If it's unbalanced, with more cold water entering the heat exchanger due to other cold water draws, it's temperature drops. Letting the drainwater heat exchanger supply the whole cold water distribution system isn't a problem. (I've been living with a 4" x 48" PowerPipe at ~53-54% return efficiency @ 2.5 gpm for going on 8 years now.)
Thanks Dana. Can you speak to the concern about adjusting the shower temperature? Do you notice fluctuations in the temperature as the drainwater warms up, or, as you say, is the increase in cold water temperature small enough to not notice? Or, do you have a mixing valve that keeps the temperature constant automatically?
I'll add a comment, have been living with a power pipe for the last 3 years and running both the hot water supply and the cold water supply for the second floor bathroom through the power pipe. Cold water never seems to get too warm for reasons stated above. As for the adjustment, takes a minute or two to get the shower water warm and then about a minute later you just tweak it down a little. I do run the shower knob a little colder than I use to but it is easy to adjust. Water from the well is very cold and it has definitely helped the energy bills.
Steve
Thanks for the reply Steve. Now that I think about it, the cold water at the beginning of the shower hasn't been warmed by the drain pipe, but depending on how far inside the house the pipe is, it has been warmed by the interior house temperature. So, (again, depending on how far of a run the water has to go) maybe by the time the cold water from outside reaches the powerpipe, the powerpipe is warm enough.
In other words, it may be a wash (pardon the pun).
I don't yet have one of these systems. I have read about and thought about these issues because I plan to install one. Therefore, you may want to give more weight to some of the other responders that have lived with one.
You hit on two reasons for not running it to certain fixtures: 1) You may actually prefer cold, such as when you want a drink. 2) If you don't care about the temperature, such as a toilet, using warm water is wasting energy, partially offsetting the reason for having the system.
You also express a concern about setting the shower temperature. The temperature of the water coming out of the Powerpipe depends on the flow rate. When the flow rate suddenly increases, such as someone else flushing a toilet, the temperature would go down. That would influence your shower temperature. I haven't run any calculation to determine whether that effect is substantial or inconsequential. If you run the water to the hot water heater inlet, the same effect can happen from other people using hot water.
I've been using a 4x48" PowerPipe since 2010. 2 months ago, I added another 4x72" PowerPipe in series with it because I was so happy with it.
During a shower the PowerPipe reaches operating temperature in under a minute. Both my showers use Delta thermostatic valves so that the temperature shift is irrelevant.
I originally piped *all* of our water through the PowerPipe (for simplicity and efficiency) but my family complained about not being able to get a glass of cold water (or being able to brush their teeth with cold) without running the water for a while.
I have since run dedicated cold lines to all the sinks in the house. Toilets get warm water (no tank sweating in the summer and avoids sucking heat out of the room on every flush) but the savings there are negligible. I just did it because I was replumbing them anyway.
With the 48" PowerPipe, it was turning 40F water into 68F water (from 100F shower/90F drain water)--almost 50% recovery.
With the extra 72" PowerPipe in series, the upstairs shower is now even more efficient, turning 40F water into 82F water (from 100F shower/90F drain water)--70% recovery.
No way to avoid the 10F drop in temperature as the water falls through the air from the shower head to the drain. So I'm actually closer to 85% recovery of the theoretical maximum.
I used 1" PEX to supply the PowerPipes to minimize pressure/flow drops from the extra piping distance. The basement PowerPipe's output feeds into the input of the PowerPipe in the ground floor wall. The ground floor shower uses just the original PowerPipe whereas the upstairs shower uses both.
I switched over to a home run manifold system (hot / warm / cold). Hot goes to the sinks and the showers. Warm goes to the toilets and the showers. Cold goes just to the sinks.
The hot water tank is fed by a 1" PEX line from the PowerPipes to maximize efficiency.
I have a real time electrical smart meter that confirms the energy savings when using the shower. Payback period has been 2 years.
Hope this helps. I'd do it again in a heartbeat.
One thing to add. I am no longer stressed when my teenagers linger in the shower. A 20 minute shower now uses as much hot water as a 6 minute shower used to!
It also means that we get 3x as many showers out of a given water tank size. We could easily replace it with a teeny one when the current one eventually leaks (we're not big on soaking in the tub so don't need the capacity for that).
Awesome John, this is great info at a time when I was wondering if it was worth the money. How is your piping set up? Do you run the cold into the bottom of the power pipe upwards, and then back down to the heater in the basement?
I just looked at both the PowerPipe (http://www.renewability.com/power_pipe) and GFX (http://www.gfxtechnology.com/) websites and notice that both recommend sending the warm water to most of the cold water fixtures. One of them recommended that the kitchen sink get true cold water.
John, there are two ways to reduce the temperature drop from the showerhead to the drain. One is to fully enclose the shower, including a lid, so that you quickly hit 100% humidity in the enclosure and there is no more evaporative cooling. That also keeps the bathroom humidity lower, so the shower dries quickly after you open the door. The other is to use a showerhead that produces pretty big drops that cool less than superfine drops. I think Delta has a showerhead optimized for a forceful feel at low flow that is much better at preserving temperature than the classic fine drop low flow showerhead.
Clay, in a typical setup, the power pipe is in the basement, so there's no " back down" to the water heater. But if you install a second segment between the first floor and second floor, the cold water would go in at the very bottom of the bottom segment, and come out of the top of the top segment before going back down to the water heater inlet.
I am another user who can report a good experience. The temperature shift after it gets going is, to me, a fun way to feel it working, not an annoyance. Plumbed to all colds except the kitchen sink and outdoor hose bib. If I were doing new construction, I'd probably run true cold to all sinks, just for drawing a glass of drinking water from the bathroom faucet, and probably also insulate the true cold to keep it true cold and avoid summer condensation. I think the prewarmed water to the toilet tank is a good idea, for the two reasons already mentioned.
Thanks Charlie. I was assuming the powerpipe would be installed as close to the showers as possible which would mean a long(ish) return line to the heater. Then again, this drain line is going to be coming down in a chase in the wall of our living room, and I was thinking about sound dampening the chase, which could include insulation in the cavity. This would help keep the heat in the pipe until it got down to the powerpipe.
What are everyone's thoughts on Heat Pump Water Heaters? They are awfully expensive. But, looks like the yearly operating costs are very nice, if the manufacturer websites are to be believed. Plus, looks like there is a $300 tax credit. If I am saving $400 or so in yearly operating costs (again, if the websites can be trusted), it won't take long to pay for itself, even if you are worried about short lifespans of water heaters.
However, lower water heater operating costs make the payback period on something like a powerpipe much longer. I don't guess I have to have a terribly quick payoff for something like that, since the copper isn't really going to wear out anytime soon. Still, it's quite an expense that could be used elsewhere.
The warm water in the cold distribution pluming issue is only problem with very substantial heat exchangers exceeding 75% efficiency. Most houses have sufficient vertical space for installing heat exchangers that tall, but if you paralleled up a pair of them you can hit those levels.
Heat pump water heaters are great for performing basement-dehumidification function, turning that latent-heat into hot water while reducing the mold potential. It affects the "payback" of a drainwater heat exchanger in conjunction with heat pump water heaters may be long in simple dollar terms, but the glacial recovery times of heat pump water heaters get heat-pump mode are reduced with showering loads, and the "apparent capacity" of the tank is also measurably larger. You may not have to upsize to more than 80 gallons for a family of four, whereas 80 gallons of heat pump water heater might be marginal if everybody is showering in the same 20-40 minute time frame, especially if one of them is a shower-hog. The payback in family harmony is pretty fast! :-)
The method I've used for keeping teenage showering times bounded is to put the bathroom lights on an infra-red motion sensor type occupancy sensor switch, set to time out at 10 minutes after the last occupancy was detected. Even at the low operating cost of the lights, the occupancy sensor more than pays for itself in reduced water heating energy use. (Full-disclosure: I've been known to hit the time-out period occasionally myself. :-) )
Awesome idea Dana. I had a thought a few days ago that would be a little more aggressive. Was thinking about wiring the light switch to a timer connected to a ball valve in the hot water line. Flip the light on, the valve opens and starts the timer. When the time is up, the valve closes and the hot water stops.
When calculating the benefit of a DWHR (looking at maybe a "thermodrain" instead of a "powerpipe"?) help me understand the real world usage.
If the drain is , say, 45% efficient, does the numbers work out like this....
90* drain temp
50* supply temp
40* temperature difference (x) 45% efficiency = 18* rise in supply temp.
Do I have that right? So the supply temp would go from 50* to 68*?
reply to Clay:
Your idea of a timer stopping the hot water will work, but if I were you, I'd keep my divorce lawyer on speed dial.
Clay: IIRC the NRCAN test protocol spells out roughly 46F incoming water and about 104F at the shower head and a 2.5gpm flow. I'm not sure what the drain temp actually turns out to be, but the efficiency is measured against the shower head output temp, not the drain, so at 45% return efficiency with 50F incoming water if you run the shower long enough it'll settle in at about 74F out of the heat recovery unit- a bit above room temp. With a low flow head it'll be a degree or two warmer, with a gusher head it'll be couple degrees cooler due to the changes in recovery efficiency at different flows. At one time I could tell you the output temp of mine, but I stopped measuring it after the first year or so.
If you want WAY too much information on the testing that eventually led to a standard test protocol, see:
http://www.regie-energie.qc.ca/audiences/3637-07_2/DDR3637_2/RepDDR/B-12-GI-23Doc1-2_RepDDRSE-AQLPA_3637-2_28sept07.pdf
If there's a cold water draw from another tap the flow increases on the potable side, which lowers the net efficiency a bit, but also lowers the output water temp by several degrees. This isn't really noticeable to a person in the shower, but it brings the temp at the other cold water tap to below room temp, but still above the incoming water temp.
This thread inspired me to do some calculations to estimate what a DWHR system would save in my house. I estimated that, at current natural gas prices, I will spend about $16 per year heating water for showering without a DWHR. (The calculation assumed that my kids will move out soon and only visit periodically.) I concentrated on showers because other uses of hot water do not seem as amenable to reduction with DWHR - the draw is not simultaneous with the drain. I also assume that DWHR has no impact on storage losses. Based on that calculation, I think I will pass on DWHR in the house I am building. I am not implying that financial payback should be the only criteria, but it is one of the things that helps me choose where to spend my capital.
Of course, the return would be much higher if I was using electricity to heat the water, especially resistance type. As others pointed out, for those using a heat pump water heater, the payback may be in terms of smaller storage capacity without getting cold showers.
If you are worried about a water heater leak just make sure to replace the sacrifice rod(s) every five years or so as well. Aside from lessening risk of a leak your water heater will last longer.
https://www.youtube.com/watch?v=kIpJDHco7hc
@Stephen, haha! You are right! It was something I was mostly thinking about the logistics of making it work, not actually thinking of implementing it. I'm pretty stupid, but not that stupid!
@Dana, thanks for the info.
@Reid, I think you are right. If I had access to natural gas, I would probably go with a gas heater and I'm not sure the savings and recovery gains would be enough to justify the expense. With an all electric house, I'm worried about recovery times and I think the DWHR system will let me save a few hundred dollars off the bat by downsizing the capacity.
I have made a few decisions. I have decided against an upstairs heater installation...just too risky and even if there is no leak, whenever it needs to be replaced I'd rather the work be done in the basement instead of dragging the tanks up our finished stairs and through the private areas of our house.
I have also decided that I will take the plunge on a DWHR. It just makes sense. If I can get the cold water supply up to 70F-75F then I can get the same performance out of a 50 gal as I could out of a 66 gal. I could get 4 showers back to back and 3 showers simultaneously.
Due to the location of the main sewer line, I'm going to have to place the DWHR in the wall as it comes down through the 1st floor. This isn't an ideal installation, I guess, if there is trouble with the device, but there is no room to put it in the basement.
The only question I have now, is if it is worth an extra $100 to go from a 42" pipe to a 60" pipe. The efficiency will go from 42.8% to 52.5%, which means the cold water temp goes from around 70F to around 75F. Obviously 70F is better than 75F, but I don't know at what point I am better off spending $100 somewhere else.