Our new Home Depot opens today. Of course, our week of appliances was last week, but we’ve still got some things to shop for.
As it turns out, hardware for a radiant floor heat system will not be on the list. After months of calculations and estimations, I [Michael] have determined that our subfloor assembly is too thick to put tubing under it and get enough heat through it, given the numbers we came up with on energy usage last winter.
It’s really, really hard to find any solid information regarding heat transfer in radiant systems, and even people trained and qualified to do these kinds of calculations failed to pick up on our floor construction. After quite a lot of searching on the internet I found a couple of mathematical formulas pertaining to heat flow through a wall, and after experimenting with a set of hypothetical numbers (hypothetical because solid information is lacking) it became obvious that our floor was, at best, only marginally suitable for a radiant floor application. We could still get some heat through the floor, and it would be comfortable, but I don’t think enough heat would make it through in sub-zero weather, and because of the lag-time the system would really only work if kept on a “slow bake” setting, with some form of additional heat going into the house for cold weather or quicker warming times. Unfortunately, the cost of the radiant installation is such that I can’t justify it without knowing it could handle all of our heating loads.
Of course, I may be wrong about this too. I am using the heat loss numbers derived from our oil consumption last winter. Last winter (and now), we had no insulation under the floor, and there is no vapor/infiltration barrier in the attic either. By this winter we hope to have both of these situations remedied. We are also now heating our domestic water seperately from our space heat. In short, I expect the heating requirements of our house to be considerably less than the numbers I am compelled to use in my calculations. Considerably less, yes, but how much less? That's the uncertainty.
New plans: Insulate the floor (without installing radiant heat: we can do this in a way that allows us to add the system later if we decide it's viable). Add a vapor barrier to the attic (easier than might be thought actually, since it involves little more than pulling the old fiberglass out, spraying in an inch of foam on top of the sheet rock, and putting the fiberglass back in: the foam provides the barrier). Fabricate a new heating system.
That last part of the plan is the most interesting. I kept most of the hardware from the old oil heater. For very little additional money I can fabricate an electric heater with enough juice to handle our worst case scenario (twenty-five below is the temperature I'm designing for). Oddly, I haven't found any electric water-heating equipment designed for my load and flow rates, but I'm still shopping, and if I don't find something to buy I guess I'll put my Industrial Mechanics degree to work again. Considering that the whole heat system is still undecided I am leaning toward the fabrication idea, because the cost will be slight and I won't feel committed to it as I would be if I spent money for a store-bought solution. Whether we buy or build our next heater, I plan to meter it so I can monitor its energy usage, and perhaps the numbers from next winter will point the way toward our ultimate heat solution.
And now... off to Home Depot!