How difficult would it be to install radient floor heating in the joists underneth an existing house?

Question

We are consideing purchasing a 'Rex Roberts' type engineered home in NH - brrr. I'm already concerned about the amount it may cost to heat this house in the winter as it sits on posts and piers and has many windows. The people currently living there said that they burned 7.5 cords of wood last year. We have easy access to the underneath of the house and the joists are visible. It does have a water heater and is supplemented by oil but I would at some point like to errect solar panels. Would it be better to do water filled tubes or electric tubes? The other option is to lift up the house and dig out a basement underneath. This is not in tune with Rex Reberts but it would give us some place to put the furnace etc which would be nice. Any advice would be much appreciated. Please ask questions if you've got them!

Answer 1

Sounds like the home is on the equivalent of a slab. Putting radiant heat below the joists would be good for the local utility, but terrible for you -- as much as 70% of the heat would be lost to the cold air surrounding those joists and the floor sub-surface. That would be like paying $13 something for a gallon of fuel. Are the underlying piers concrete? If so, one answer is to dig a trench around the structure (depth depending on where you live) frost in the northern US extends down as much as 4 ft. So, you could dig a 4 ft trench all around (about 1 ft wide) and install rigid styrofoam insulation (minimum 20 R factor), then back fill with gravel (underneath) and then 4 inches of soil (outside the insulation only). If they are wooden piers -- if so you might have to consider replacing.

Another consideration is drainage. If your home is on piers, you probably do not have weeping tiles surrounding it. In that case, you would need to also install weeping tiles to keep moisture from permeating and destroying the insulation you install.

Without knowing all the details, I would recommend contacting a local foundation contractor and asking them for their imput.

Depending on the size of your home and the length of time you expect to live there, an installed basement will always be the best answer (and potentially give you more living space (e.g. family room or play room). But, it`s expensive, from jacking up the existing structure to laying footings, forms, concrete pouring, weeping tiles, waterproofing and backfilling.