Old House Q & A:
We live in an old house in upstate New York and we’re thinking of replacing our very old boiler with something more efficient. Winters are pretty cold here. We keep hearing how wonderful ground-source heat pumps are. Is this a good option for an older house?
Possibly. Ground-source heat pumps are attractive for a couple of reasons. They don’t burn any fuel to produce heat, at least not directly, and heat pumps can cool your house as well as heat it. They’re also more efficient than many conventional boilers and furnaces.
Ground-source heat pumps work like a refrigerator in reverse to absorb and concentrate small amounts of latent heat gathered from the earth or a body of water. Heat pumps, like refrigerators and air conditioners, rely on something called vapor compression to work.
Even in winter, the earth is relatively warm six or seven feet below the surface. Tubing filled with a non-freezing liquid pulls some of the heat from the ground and carries it to the heat pump. The tubing can be placed in horizontal trenches, or in vertical wells.
If you live near a pond or stream, water also can supply the small amount of heat that’s needed for the heat pump to do its magic.
Efficiency Is the Name of the Game
Energy efficiency is one of the biggest advantages of a ground-source heat pump. For every unit of energy it consumes to run circulation pumps and the compressor, the heat pump produces three or four units of energy in the form of heat. This is what manufacturers call the “coefficient of performance:” the higher the number the better.
By contrast, electric baseboard heat is about 100 percent efficient, and the best gas furnaces on the market are about 95 percent efficient. Getting a lot of heat for the buck is why ground-source heat pumps get such rave reviews.
Ground-Source Heat Pump Caveats
First, there’s all that tubing that must be put in the ground–hundreds of feet of it. If you choose horizontal trenches, you’ll need a very generous back yard. The excavation equipment your contractor will bring in won’t be kind to your lawn or your gardens.
Drilling a new well for the tubing is another possibility, and a practical choice when you live in town. You won’t need nearly as much open land, but drilling a well can be pricey. If you already have a well that produces lots of water it may be possible to tap into the supply for your heat pump, but that’s a long shot.
Because installation is so much more involved, ground-source heat pumps typically cost a lot more than other kinds of heating systems.
If you can handle the cost and want the option of central air conditioning, a heat pump might be just right for your situation. Another option is to wait until the new generation of cold weather air-source heat pumps becomes more available. You’d get many of the same benefits, but at a lower cost.
For now, replacing you aging boiler with a high-efficiency gas boiler would be less disruptive to your house, and to your wallet.