Going All-Electric in a Cold Climate
ChrisStratton
| Posted in General Questions on
We are considering a heat pump plus some local radiant heat for a vacation cottage in western NH. Is it safe to have ONLY electric in the region? Any thoughts on ductless vs ducted heat pump?
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Yes. A fossil fueled furnace will be similarly useless if the power goes out. A wood stove can provide backup for outages, provided someone is home.
+1. Woodfire is what I went with. They've come a long way from the dragon smoke belchers of my Grandpa's days.
EPA biomass requirements have pushed designs. There's now hybrid woodstoves (catalyst + secondary combustion), manual (thermostatically) or electric baffle adjustments, etc. That's gotten emissions well below the 2020 requirements of 2g/hr and efficiency >80%.
It's not carbon 0 but it's much cleaner now, especially if just a backup.
Safe? Yes. Cost-effective is a different question. What is your cost of electricity and what would be your alternative fuel and what does it cost?
We had several posters here from New England last winter who were shocked at how much their heat pumps were costing to operate. It turned out they were operating as designed, they just had really expensive electricity.
I think our rates from Eversource peaked at around $0.313 / kWh last winter; it may have been cheaper if you used an alternate energy supplier. Propane and natural gas had significant increases as well (and probably fuel oil too). No matter which energy source you used a lot of people were hurting due to fuel costs.
This will be a vacation home - so, we can drop the heat when not occupied to something like 50 degrees F.
Then you’re fine!
Thanks! Any thoughts on ductless vs ducted heat pumps? I am thinking of two units - one in basement, one upstairs, and supplement bedroom/bathroom w/ radiant heat.
Ducted all the way for quality/redundancy/future proofing. It’s much better for distribution, dehumidification, filtration, efficiency (vs a multi-split), and it’s easy to incorporate backup resistance, furnace, etc right into the ductwork. Then some electric in-floor radiant if you want for kitchen/baths.
If you’re trying to cost optimize, ductless on the first floor plus some radiant baseboard upstairs probably comes in cheapest.
Thanks, Paul. We are looking at CEILING radiant heat for bath/bedroom. Had not considered kitchen.
Are you thinking just resistance radiant heat? I haven't seen that for installation other than in floors.
A properly design heating system is sized to maintain the building's heat. A 20 degree setback is never going to work well. You will not get warm until Sunday when you are ready to leave.
User: A small house like this, if it's tight and well insulated, will only take a few hours to warm up.
Unless they’re arriving on design day, there will always be significant excess capacity
I have a seasonal house in Rhode Island. Last February I arrived there on the coldest recorded day in RI history, -6F, 15 degrees below design temperature. It took a while for the house to warm up!
A "properly designed" system is sized to maintain a fixed temperature on the near worst-case day of the year, usually with a little extra just in case. That means that (for heating season), the colder it gets outside, the longer it will take for the system to raise the indoor temperature. At some point, you get to where you can't raise the temperature, you can only maintain it, and that's when your heating system is running all out just to compensate for the heat losses of the home alone. Anything past that point and you are "losing the battle", as I like to say, which means that your indoor temperature will decline in sync with a falling outdoor temperature, and your heating system can only maintain a somewhat fixed differential between indoor and outside -- it can no longer RAISE the indoor temperature AT ALL.
Set backs work if your system has excess capacity. As you approach that "losing the battle" point, setpoints take longer and longer to achieve, and eventually you can't, in which case a reduced nighttime setpoint means you can never get to your daytime setpoint the following day. That is a situation to be avoided. Heat pumps tend to not like setbacks, and would prefer to maintain a constant temperature all the time.
If you really want to maintain a setpoint much lower while you're away, but you want to bring the temperature up while you're there, I would let the heat pump do the "maintaining" of the setpoints, but put in enough electric resistance baseboard heat to be able to "move" from the low "away" setpoint to the higher "we're back" setpoint. This won't cost much to do, since the electric resistance heat will only be used for a relatively short period of time when you get back. The heat pump should be the cheapest way to maintain the setpoints in the steady state though.
Bill
I agree. I also don't think radiant ceiling is a particularly good choice for this application, because it has a greater lag time than say radiant baseboards or even just a resistance coil in the heating duct.
I have a similar small cottage up north minus the basement. The place is heated with a single hyper heat wallmount. There is baseboard backup mostly just in case set bellow the setpoint of the wallmount.
This works well, about the only issue is the wifi controls for it can't put it into freeze protection mode so you have to set it manually before leaving and not adjust remotely until the place needs to be warmed up. The wall mount does a decent job of bring the place up to temperature as long as you give it about a day or so, no need to run the baseboard heaters as well.
Make sure whatever hardware you pick can actually be turned down to around 50F, not all can.
If the basement is unfinished, I would go with Paul's suggestion of a ducted unit. You can get something like a slim ducted hyper heat unit mounted to the basement ceiling and home run flex ducts to each room. This way a single unit can heat/cool the whole place. Getting ducting installed seems to be very costly, so this might only make sense if you can DIY the ducting. Even without ducting, getting the unit installed there and letting run to overheat the basement will do a pretty decent job of also heating upstairs, think of it as poor man's heated floors.
Make sure you utility area is well contained, all the piping is on inside walls and it has some form of backup heat. If your power is unreliable, a small through the wall propane heater there might be a good idea.
I'm pretty much settled on a Martin Direct Vent (through wall) propane for backup heat. Also, it should serve well if we arrive and the house is at "away" temp.
Let me just spitball some numbers.
I leave my second house unheated in the winter and drain the pipes. It takes about 12 hours to bring it up to temperature when I visit. It has an almost 50-year-old boiler that is oversized by about 50,000 BTU/hr. So let's say it takes 600,000 BTU to raise the interior temperature from 30F to 70F, that's 15,000 BTU per degree. Most of the stuff inside a house has a specific heat around 0.5, so that would mean about 30,000 pounds of house inside the envelope. Based on the amount of drywall, flooring and tile that goes into a house I think that's right at least in terms of order of magnitude.
If your house is at 50F you'd only need half as much heat, or 300,000 BTU to get it up to 70F. Doing it over the same 12 hours means 25,000 BTU/hr. You don't want to oversize your heat pump by that much, but if you had resistance heat that's about 8,000 Watts of resistance heat. Running that for 12 hours would take about 100 kWh of electricity, or about $30 worth at 30 cents/kWh.
Note that the amount of heat needed to warm the house is independent of how well-insulated the house is and the heating load, it's determined by the heat capacity of the interior materials.
Note that using a remotely controllable thermostat lets you trigger the "warm up" cycle whenever you want, before you arrive. This way you never have to wait for the warming up to happen. I do this myself at my own home when I'm away, using the Ecobee thermostats that I use. Works great.
BTW, I would add that a better insulated home would still be limited by the need to warm up all the "stuff" inside, but would require less total input energy when losses through the structure were included. Basically you'd need the same energy to warm the place up, but less total energy overall due to lower losses needing to be overcome during that warmup cycle. Basically insulation effects the steady state losses only, and does not change the amount of thermal energy required to heat up the "stuff" inside the envelope.
Bill
My boiler runs to maintain temperature even when the thermostats are off, so I can't turn it on and off via thermostat. So I put an internet-enabled switch in series with the main on-off switch.
I need to find a new one, the one I have is probably about a dozen years old and the manufacturer just announced they are discontinuing support this year.
FWIW, I've had great success with KASA brand smart switches. They interface perfectly with Hubitat, too.
Yep that should be safe enough as l0ng as you have back ups for heat and light. Maybe install solar panels and a battery alongside so you can throw on a couple of electric heaters if required.
You need a very substantial amount of battery reserve to accomplish any significant amount of heating this way. For some perspective, a typical “car battery” size battery will run a typical 1,500 watt space heater for around 15-20 minutes — not much.
If you want long-term backup power, a conventional generator is a much better choice here, or a propane fired heater that does not need electricity to operate.
Bill
I wouldn't put in a woodstove. A wood stove, with proper clearances, can take up 16 to 25 sq' of floor space. Also, with all the dangers I've been reading about lately regarding tiny smoke particles causing health problems for millions of people in the US I'd rather not be burning wood inside a small cabin. Plus, most wood stoves are hard to get "running right" - either it's blazing hot, or cools down too fast, it's dirty, there's constant preparation work getting firewood cut and seasoned, etc.
I'd rather install a direct vent propane wall heater that is set to come on when the thermostat drops below a set point. This type doesn't use any indoor air for combustion and vents all byproducts outside.
Something like this:
https://canadianoffgriddepot.com/products/martin-direct-vent-propane-wall-heater-with-built-in-thermostat-20-000-btu