Let’s think of a poorly insulated home with a 30 year old furnace that runs at a 65% annual efficiency. The bills must be really bad. We could replace the furnace with an 85% efficiency unit and save about a third, or we could attack the insulation levels. However, upgrading the insulation reduces the heating requirements and reduces the potential savings with the better furnace. Basically, if we save a third of a lot, it’s a lot, but if reduce the load, we save a third of less.
So, let’s upgrade the attic insulation from the existing, maybe R-13 to R-38. That’s got to help. Now, let’s insulate the ceiling of the basement, an often overlooked measure but seriously important. These are two of the least expensive measures a homeowner can take, and they have significant results. Insulating and air sealing duct work in unconditioned areas is also often overlooked. Replacement windows are an option, but they are pricey, as is wall insulation.
The question is when do we consider geothermal? My answer is after all reasonable conservation measures have been taken. If we can take a home that requires 75,000 btus to heat , and knock that load down to 45,000 btus through insulation measures, it not only reduces the operating costs, but also reduces the installed cost of a geo system. Equipment size and well depths go down. Most often, the reduction in installed cost of the geo system offsets the cost of the insulation measures.
Oddly, the operating cost savings for a geo system increases with the amount of run time a geo system has. In the above case, a six ton geo system would have more savings for the home with no improvements to the insulation. However, a right sized four ton unit would cost much less to install and run in the upgraded insulated home, The combination of insulation and the smaller and cheaper geo results in the best payback as well as the best result from an economic and environmental perspective.
The bottom line is that we need to minimize the heating and cooling requirements of a given space, and then install a right sized geo system for the job.
I’m all for conservation, and to be honest, I sell and install geo systems for a living, but insulation and air sealing come first. After we did everything we can cost effectively do about heat loss, we can then talk about geo.