With temperatures dipping down to -30C (-22F) at night (colder with the windchill), we've had a pretty frigid couple of weeks. It's cold enough that the dog's paws hurt when we go for walks, cold enough that the oil froze in the pipe between my neighbour's oil tank and his furnace, and cold enough that one of the hoses in our generator froze solid; one of eight the shop had seen that week with the same problem.
So how does the house behave when it's his cold? Pretty well I'm pleased to report. If the sun is out the front part of the house will get up to 25C (77F) during the day and will hold most of that heat until we go to bed. Of course with the quantity of glass we have across the front of the house we do bleed heat, and the colder it is the faster that heat goes.
If there is no sun though the floor works pretty well. It can hold the house comfortably around 20C-21C (68F-70F), trying to go any higher seems a waste of propane, we just wear sweaters. Because the way radiant floor systems work it's a 'slow heat'. The slab is heated to a certain temperature and from there it just radiates (obviously). But we have a huge interior volume of air, much greater than most houses of the same size because we have such high ceilings. At its lowest point our ceiling is over ten feet high, at it's highest it's around seventeen. The floor just cannot react fast enough to compensate when the sun goes down. As a result we've moved a fireplace up to near top spot on the wish-list. We built a re-enforced pad into the floor to carry the weight of a masonry fireplace but have decided that what we need is actually just an airtight insert or a good woodstove. We need something that can heat the air quickly, but can also stop relatively quickly. The last thing we want is to light a fire on a cloudy morning in a masonry heater, than have the sun come out and have the stove radiating heat all day long. We'd cook ourselves out of the house!
I've been running around with the caulking gun sealing cracks and hunting for drafts, and there have been lots. At this point I have gone through more than three dozen tubes of caulking and I have one piece of advice for those building a house: the expensive caulk is worth it! Buy the best stuff you can find, we've used various grades around the house and we've had all sorts of failures wherever we used cheaper caulk. It might cost more up front but it's worth it to save the aggravation and cost of having to do the same job twice.
Hi Glenn,
I was wondering what temperature you keep the floor at? I'm asking because I've always read that a low response time was one of the advantages of radiant floor heating in a concrete slab. I forget the exact numbers but number of BTU's in your air even with the large volume is quite small compared to the BTU's in your floor. Maybe the btu's of radiant cooling from your windows is more than your btu's of radiant heat from the floor? Do you have coverings for your windows at night?
I've read a book by Dan Holohan that explains the fundementals of radiant heating which you might find interesting. Hydronic Radiant Heating - A Practical Guide for the Nonengineer Installer his site is www.heatinghelp.com which is useful as well.
Thanks for the update, your whole story keeps me inspired for building our house.
Ian
Hi Ian,
I have had endless problems with the floor which I haven't blogged yet. We've had 2 valves get stuck, problems with the tank, problems with the boiler, and our installer has been the very soul of patience and good-humour, especially when the problem is caused by my oafish meddling.
The floor is controlled by two thermostats and two aquastats (one each per zone). The thermostats (air temp in the house) are set at 21C. the return water aquastats are set at 35C. This prevents the floor from overheating. The presumption is that if the liquid can go all the way through the house and come back at 35C then the floor is plenty warm enough, and it should just be radiating.
Thanks for the book recomendation, I have several books on hydronics and frankly don't understand any of them, the floor/hot water system still bewilders me. Today however after another round on the phone with the installer I think I FINALLY have a handle on what all the settings etc mean. When it is fixed I plan to do a big blog entry.
As for the radiation of heat from the floor vs cold from the windows I suspect that when it's -30C the windows are quicker. There's just too much glass. But otherwise the floor should be more than adequate! We've talked about coverings but our wall o' windows is 55' wide and 15' tall - and frankly any covering that we can think of would be too ugly/obtrusive/heavy. As for individual covers, there are 46 windows and 6 doors across the front of the house, I'll rather deal with the cold than making separate shutters for each, plus removing/installing each day. One thing that I will olikely do next year though is make insulated shutters for my north windows since they perform no function at all in the winter.
GH