The heat is on...
January 21, 2017 1:51 PM   Subscribe

Most efficient way to handle thermostat for cabin with electric baseboard heat?

I have a cabin in Wisconsin with electric baseboard heat. It is about 400 square feet. I am up there most weekends (on average 3 out of 4 weekends). I have Honeywell programmable thermostats. The foundation is concrete slab.

My question is....what is the most efficient/cost effective method of setting the thermostat? I had been setting it to 40 degrees F while I am gone and then turning it up when I get there. But, December's bill was more spendy than I'd like. The building is newish and has standard 2x4 construction and standard insulation. the slab has standard insulation under it. 3 inch foam if I recall...whatever is standard recommended. it actually more efficient to keep the whole building a little warmer (say 55 F) so that I am not continually dumping electricity to heat up a cold slab? Or is it more efficient to continue to set the thermostat to 40 while I am gone? Or some other strategy altogether?

Regardless, I'd prefer not to turn off the heat altogether cuz I don't want everything freezing solid and I don't want to wait a billion hours to make the place comfy.

At some point I will likely put a heat pump wall unit in as they are more efficient down to a certain temp. But that's for the future.


posted by ian1977 to Home & Garden (13 answers total)
You are definitely not going to use less energy by keeping the thermostat higher. This is one of those holy wars of how to deal with an empty house.

If your house has running water, 40 is already a little dicey depending on how the plumbing is set up. You do have plumbing right? Most people recommend 50. Does the cabin have internet? Do you have friends there? Reason I ask is because the best approach if you're concerned about the billion hour wait (I, too, spend weekends in a house that is usually hovering around 50 when I get there, I feel you) is insulate it well (plastic up the windows and any leaky spots) keeping it as cold as possible but then turning the heat up a few hours before you get there. You could do this if you had a thermostat that spoke to the internet. If you have internet.
posted by jessamyn at 1:58 PM on January 21, 2017 [4 favorites]

No plumbing. So pipes freezing isn't a concern. Though once when I accidentally turned the heat off the mouthwash froze, cracked the plastic, and then slowly leaked as the mouthwash unfroze. Gross.

No internet yet. But I would love to go with a setup like that someday.
posted by ian1977 at 2:00 PM on January 21, 2017

It is always more efficient to turn the thermostat down as far as possible.

Think of it this way: Your energy use isn't really to heat up the space, it is just to replace the heat that escapes through the walls, floor, windows, etc. The lower the internal temperature, the lower the heat loss, the lower the energy use. You do use more energy to heat up the place when you turn the heat up, but you get that energy back as the place cools down once you leave, so you can safely ignore it. All that matters is the temperature difference between inside and outside, multiplied by time.
posted by ssg at 2:19 PM on January 21, 2017 [3 favorites]

But wouldn't the thermal mass of the slab be a factor?
posted by ian1977 at 2:20 PM on January 21, 2017

Baseboard heating should warm the place up from very cold fairly quickly, even with 2X4 wall. You know, "standard" is 2X6 and R19 insulation. You don't get R19 with 2X4 walls. I'm not sure what you're asking here. There's not advantage to maintaining a higher (or lower) above freezing temp over time (when you're not there).
posted by humboldt32 at 2:21 PM on January 21, 2017 [1 favorite]

But wouldn't the thermal mass of the slab be a factor?

Turning the thermostat up when you arrive will heat all the air in the cabin to room temperature, and the slab will slowly draw heat from that air, but the heating effect of the baseboards will easily out pace the slab's draw. Once the air is room temp, you won't notice the floor sucking heat.

Heating it while you're not there is doing nothing, (beyond keeping things from freezing). Then energy consumption to bring the slab back up to temp is minuscule compared to the energy consumption to maintain it over time while you're gone.
posted by humboldt32 at 2:27 PM on January 21, 2017 [3 favorites]

Have your stats turn down to say 35F when you leave and then have them turn on before you arrive to your room temperature. You will have to experiment to see how early the stats need to turn on to get the space livable before you arrive.

ian1977: "But wouldn't the thermal mass of the slab be a factor?"

Only in so far as it takes time to heat the slab. Keeping the slab at 60F is going to use more energy than letting it fall to 35 and then heating it back up to room temperature.

You might want to consider heating your floor if it is currently bare concrete. Doing so will let you maintain a lower air temperature (and is more comfortable to boot).

humboldt32: "Baseboard heating should warm the place up from very cold fairly quickly, even with 2X4 wall. "

That'll depend on the ratio of heat loss to watts in from the BBHs. A badly specced system could actually fail to maintain room temperature during extreme low exterior temperatures. A hugely over provisioned system would heat the space practically immediately.
posted by Mitheral at 2:27 PM on January 21, 2017 [1 favorite]

The heart of my question is do I waste more energy getting from 40 to 70 in a short period of time 3x a month than I would if I costed along at 55 and jumped up to 70 3x a month with the consideration of large thermal mass in the equation (i.e. Concrete slab)
posted by ian1977 at 2:28 PM on January 21, 2017

Cheapest to let the temperature fall as low as possible and then heat the cabin from that much lower temperature. The thermal mass only effects the rate at which your cabin heats; keeping it warm will not save money.
posted by Mitheral at 2:31 PM on January 21, 2017 [3 favorites]

Thanks for all the answers. Mitheral answered the question that was in my head but I didn't ask very succinctly.
posted by ian1977 at 2:38 PM on January 21, 2017

BTW the same concept applies even if one is heating their space every day. Setting a set back stat to as low as livable temperature at night on a home always saves more energy than keeping one's house at a higher temperature. This is because the lower the delta T between the inside and outside the lower the energy loss from the inside to the outside.

This is fairly self evident if you consider the extreme case: if the interior is the same temperature as the exterior then you lose no energy (and your BBHs never turn on). Heat transfer (and operation of the BBHs) only occurs once there is a differential. And the higher the differential the higher the rate of heat transfer (and the longer the run cycle of your BBHs).
posted by Mitheral at 2:39 PM on January 21, 2017 [1 favorite]

Studies have shown mixed results for short term fluctuations, i.e. setting the temp lower at night. This is due to inefficiencies in the heating process, both in the equipment and in how warm air moves around the house. For example, in warming the house quickly, you may overheat some areas before other areas get warm. Obviously, the smaller the building, the less significant this problem is.

For long term fluctuations, e.g. going away for a week, a low temp is better, but as noted above, you want to be careful about plumbing. I would suggest actually trying to measure how cold the water is in the pipes by running some into the pan and sticking a cooking thermometer in it. You may get a bit of reassurance or big scare, either would be better than resorting to worry.
posted by SemiSalt at 9:11 AM on January 22, 2017

A friend of mine had isomorphic issue: what size pool heater to install, when only needing to heat the pool for the occasional party. He ran the numbers and realized that putting in a 3x capacity heater (at more expense) but leaving the pool cool most of the time was much cheaper. When the party comes, he can just blast it and heat it as needed.

If your biggest worry is frozen mouthwash, then just turn it off.
posted by soylent00FF00 at 6:31 PM on January 22, 2017

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