Saturday, December 26, 2009

Heating a tiny house

Well, we followed the suggestions as to what insulation to use to build our tiny cottage (2" thick rigid foam planks sealed around the edges with expanding soy foam). But because of the ratio of exterior walls to interior volume, and that we have no air pockets like a heated hallway or closets, we are chillier than I had expected us to be.

I think because it's a very tiny home that takes less energy to heat, I expected it to be toasty inside all of the time. Oh, not so...

On average, we run a 20 to 25 degree difference compared the outside temperature without running the heat, or summertime fan, during normal working hours. (If we never turned on the heat at all this would not be the case.) It turns out that we're cooler in the heat of summer yes. But also cooler in the cold of winter.

There had been an unusually cold day (29F degrees) last month but then it quickly warmed up again. We were comfortable that night so I thought that if the cold weather lasted longer that we'd stay comfortable enough. This past week/current week the high was/is supposed to hover at 32F and the low will be about 22F. This has meant a steady cold and it's been much trickier to stay warm.

Last night we'd had the Newport 900 boat heater on for about 4 hours. At 9pm, the outside temperature was 33F, the inside was 67F with the interior humidity at 48%. This morning at 5am outside was 24F, inside was 52F, and (since we don't keep the dehumidifier on at night) the humidity was 59% . Not as toasty as I'd like to be inside. We were used to turning the heat on very infrequently before moving into the cottage, and we'd simply wear a sweater and slippers at home. In this place, we use more fuel to heat the place and we wear an extra sweater. (We've become quicker at getting dressed first thing in the morning too!) If producing less of a carbon footprint is the reason you want to live in a tiny house, you'll have to figure out how to use less fuel for heating even if this is less expansive than heating a larger space. Insulation is the key; I have no definitive answer as to what to use yet though.

We have winterized, and will continue to do more as we think of what else can be done. We know the following information for sure because (tech geek that he is) Jeff bought two scientific temperature rods that he hooks directly up to his laptop for digital readings:

In early November we started by buying honeycomb shades to better insulate our windows and they keep the inside warmer by 6 degrees. Yes, we bought Low E double pane windows and installed them properly. We have 10 windows plus one skylight.

The industrial felt floor cover feels warmer to the touch than the wood floor, but we've tested it against the wood floor and it doesn't help the inside temperature at all.

I have stuffed dense foam into the 'attic fan' vent louvers and the bathroom exhaust fan outside as well as stuffed the skylight area.

We bought a dehumidifier because we started to get condensation on the window interiors and we don't want mold to form. Before we had the gauge to measure the humidity, the first 36 hours the machine was on we filled the 12 pint reservoir. Since then we leave it on from 5am until about 8pm and it takes two weeks to fill. We now hover between 49% and 60% humidity (gotta breathe but we don't cook at home and we shower at the gym or indoor pool each morning after we workout). We like how the dehumidifier evens out the temperature in the cottage by blowing cooler air up so that the heated air is forced downward. We sit downstairs and want it warmer until we go upstairs to sleep. The sleeping loft area gets heated fairly quickly by the two of us breathing since it's about the size of a two person tent.

We bought a heated water hose from and it works exactly as advertised.

We've thought about insulating drapes but have decided to wait on those. I need to do more research.

If we were to build another tiny home, or to make some suggestions, it would be:

  • Buy more heating power than you think it will take if you live in a place that gets cold. (Will a radiant heated floor work in a tiny mobile cottage? I don't know.)
  • Either buy a different type of insulation or beef up the 2" thick panels because it doesn't retain heat well since these structures are all exterior walls.
  • I don't know if having a full loft, rather than a partial loft, would keep it warmer downstairs in the winter. It might, but it might also be much hotter upstairs in the summer. We like the air circulation and light. The high ceiling in the living area makes it feel larger so I'm not sure we'd change this design.
  • Jeff suggests fewer windows.

We hope that you're staying warm this time of year.

Until Spring we'll be posting to this blog only once a month. Currently we're fine tuning the cottage to make it more comfortable so there's not much to post. As it warms up here though, we'd like to settle in a bit more by building a small deck and planting a vegetable garden.

Happy Holidays and have a very Happy New Year!


  1. You might try filling the (it looks like) inch of open space on the inside surface within your walls with some spray in foam where the ridged foam boards didn't fill. Maybe removing a board from the top of the wall or pulling off molding and drilling holes will give you access to spray in the foam. Infrared camera would be great to find out where the problem is (maybe you can borrow one).

  2. Hey, I am sorry to hear about your heating issues. Wish I could offer some advice.

    Thanks for your update on the no-freeze hose. I am glad to hear that is working well for you at least.

  3. You don't have any thermal mass. I know this goes against keeping the house light enough to transport but you need something inside to 'soak' up the heat and keep it there. Because it is such a small space your air exchange (losing all the heated air) is probably pretty high. Maybe something fill with water...that could store the heat and let it keep the temperature more constant in your little house. You might look up trombe wall. ...but to a smaller degree to match you house.

  4. I'm sorry to hear of your heating troubles but Matt there above got it right. No thermal mass and high air exchange. You could invest in a venmar system but I doubt they have them sized small enough for your place.

    You could look into a small stone stove or a rocket mass heater (all probably too heavy for what you've got) but that would solve your problems.

    good luck!

  5. My daydream tiny house includes one of these tiny wood stoves: They're heavy and they need a chimney, but the cast iron of the stove itself offers some thermal mass, so it will continue to radiate heat after the fire goes out.

    I hope you find efficient ways to stay warm this winter. I wonder if something in the walls is conducting heat outwards more than it should be, and how you can detect that and insulate against it specifically if so. Stay warm, and keep having fun!

  6. Have you reversed your ceiling fan so that the paddles are pushing the warm air down from the ceiling?

  7. Well I'm glad to hear that you haven't frozen yourselves solid but sympathetic towards your plight. Ther person I'm rooming with doesn't like the heat on at night and there's inadequate insulation so it's usually about 12C (in the 50's F) in my romm before the furnace kicks in.

    I hope you find a solution to your heat problems and I can't thank you enough for bringing the winter warmth issue to light. I think many of us will be learning from you well into the future. And I've looked up those marine furnaces before - wood stoves give such warmth and they dry the air out too.

  8. I'm trying to posting things as they happen that are not obvious that I would want to learn about before building a tiny house. I love to see a discussion follow a post!

    It can sometimes be a bit colder inside the cottage than I'd expected it would be but I would NOT trade this adventure for some other warmer place. We're fine tuning the place and figuring out what works and what doesn't as we go. I would consider heating as being more of a 'challenge'; not yet a 'problem'.

    I'm still very happy that we built this place and we are very excited to be living pretty comfortably in it too.

  9. Hi,
    We live full-time in a small travel trailer in the Okanagan Vally (BC Canada). We did several things which helped keep us warm. 1) Put "Reflectix" on the outside wall of every enclosed space (in closets, cupboards etc). Keeps your radiant heat from escaping. 2) Our primary heat is from two 24 x 24 x 1/4 inch panel heaters mounted on the wall. These use only about three cents-worth of elec. an hour (each). They are on plug-in programmable thermostats. The heat is very steady, not hot and cold like a furnace, and they consume no oxygen. We had two in our last trailer, and when we sold that trailer and bought this one we bought two new panel heaters. We have a washer/drier, dishwasher/fridge, MW, TV, two computers, all the bells/whistles, and the panel heaters and our power bill consistently comes up the lowest in our park of about 25 full-timers. This is similar but not exactly the same as ours. Looks like it has a built-in thermostat.
    Deb -

  10. Deb,

    We'll look at those heaters for next winter. I like that it consumes little energy and that it's so slim. To have something on a timer to go on a bit before we have to get out of bed would be nice.


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  12. Hi Jeff and Arlene,

    We are mid tiny house build and are facing what feels like a major quandry and wanted your input as you did your share of research for your own build. The builder we bought our plans from and many other tiny home builders do not vent their ridges/roofs, and use something other than closed cell foam insulation on their cathedral ceilings, which is advised against in every bit of building science we can get our hands on because of the condensation moving from the inside out in the winter and causing eventual rot/mold on the insulation and/or sheathing. We see you used rigid foam insulation, but how did you decide not to vent your roof? Thank you!

  13. Anon:
    It turns out we do have a bit of a vent. Take a look at this picture:

    From the top you can see there is a gap between the insulation and the outer sheathing. At the top there is also a small gap between the top of the sheathing and the ridge board. Here is another pic that shows this:

    Now the tar paper does go over the roof line but there is still a gap at the end and the metal roof allows some air to get in/out under that.

    So, from the inside out we have:
    1/4 inch wood paneling
    0.6 mm plastic vapor barrier
    2x4 studs with 2 inch foam and an air gap
    Tar paper
    metal roof

    with some strategic air gaps.

    Now, not having done this before I have no way of knowing how well my gaps are working and I really don't intend to take the roof off to check. I can say we have no leaks and no smells and that makes me happy. :-)


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