Q. Our two-story home was built in 1900 and has an in-floor gas heating unit-- the type with an open grate in the floor. We recently put on an addition to the rear of the home with a heat pump. My husband is determined to get some sort of alternate heat into the older part of the house, claiming the grate set-up is unsafe and inefficient. I like the gas heat as it is much warmer than the heat pump in the new addition. The gas unit is about 13 years old. I like the gas heat in that it continues to work w hen the electricity is off. Also, it seems to heat the upstairs very well, unless our guests shut their doors. We do not use the second floor except for guests. Can you suggest what configuration would provide the best and most efficient heat for our str ange situation? We have considered a “Mr. Slim” type unit in the upstairs, but we would also need to heat the downstairs part of the old house. Who does one call to give us the down and dirty about what would work best, without the bias of a product they sell?

A. Your dilemma is a common problem in an area such as ours where some of the housing stock can be hundreds of years old but being so desirable we tend to preserve it and add on. The trouble that we get ourselves into is the difficulty of combining tech nologies, like the heat pump system, with a structure clearly not suited for it such as the older section of your home. You are going to have to apply educated common sense to the problem to arrive at any sort of livable solution.

Since the new section and old section are openly connected, the air between the two will mix. The nice warm and rapidly heated air from the gas floor furnace from the older section can waft over to the thermostat of the heat pump in the newer section foo ling it into thinking it has done such a super quick heating job that it will stop calling for heat and then that section of the house will go cold. Summer air conditioning presents a separate set of problems.

Of course you prefer the very warm temperatures that come out of the floor furnace in contrast to the heat pump’s performance. The air that comes out of a heat pump’s floor register is only 14º to 18ºF degrees warmer than the air entering the air retur n register while the air coming from the gas furnace is in the 140ºF range-- a warmth you can really feel. Your husband is correct in his assertion that the gas is inefficient relative to the cost of gas consumption versus heat pump operation. Like any fuel burning appliance they can be unsafe if misused or poorly maintained. Their basic design is safe and UL approved or they would have been outlawed years ago. That being said, I recommend installing Carbon Monoxide detectors in any dwelling with any fossil fuel heating device in it. That’s just common sense.

But quantifying efficiency between a heating device in a 106 year old structure and a brand new heat pump in a tight, well insulated structure is an exercise in futility so my recommendation is come to a compromise on comfort versus cost. Your idea of a dding the slim wall hung split system heat pump in the upper level for both heating and cooling is just what I would have recommended to narrow the gap between cost and efficiency for old section. Look to air-tightness of the old windows and doors and m ake improvements there. Is attic, wall, and underneath-- basement or crawl space-- of the older section insulated and how well? A judicious application of ceiling fans can help move air and in so doing will mix the warm and cold. The inherent disparity between the old and new sections of your home are just part of what gives it its character and, sure, you could hurl heaps of money at the whole place replacing old and shoehorning a new set of systems into it but I think you’re better off working with what you have. Unless, of course, you hit the lottery.