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Why Insulation Matters in Geothermal Sizing

Updated: Mar 1, 2021

We, at King Energy, strongly believe, and know from our experience, that every home is a system. By this we mean there is a strong interplay between factors such as insulation levels, airtightness, heating system efficiency, system capacity, usage patterns, solar gains, and more. All of these factors impact heating and cooling costs. To provide the best results when considering the myriad of conservation options a homeowner can select from, we recommend the Home Energy Solutions (HES) Program that is sponsored by the utility companies. They will take an unbiased and comprehensive look at your home and recommend conservation measures in a way that each is prioritized.

HES contact number to get started: 1-877-WISE USE (877-947-3873)

Your house is a System

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 of admittedly high consumption, or we could attack the sub-standard insulation levels and also save around a third. It may seem to do both saves two thirds. It doesn’t work that way.

Insulation levels need to come first, and you save the first third. The system efficiency upgrade then saves a third of the new reduced consumption. Upgrading the insulation reduces the heating requirements and reduces the potential savings with a better furnace. Basically, if the furnace saves a third of a lot, it’s a lot, but if we reduce the load, it saves a third or less. It’s always best to insulate first 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. The HES contractor will also perform a blower door test to help expose air leaks in the home, and will often fix the problems right there. Insulating and air sealing ductwork in unconditioned areas is also oft-overlooked. Replacement windows are also an option, but they are pricey, as is wall insulation.

To further illustrate the relationship between the ‘envelope’ and the heating system, let me relay two recent episodes from the field.

I had three calls from a brand new homeowner that she couldn’t get the house over 62 degrees. These all occurred within a week and started exactly after they moved into their new home. The unit had been running a few weeks before. I kept finding the geo system doing its job. On the third visit, I explored a little more and found that the insulation crew never blew in the fiberglass required in the attic flats. What was calculated as an R-38 surface was really only an R-1.7 surface. We got the insulators out there post haste, and since then, all is well. There was nothing wrong with the heat pump. It was being asked to do way too much. The owners didn’t think to call the insulators, they called me.

On the same day as my discovery on the above home, I was called to investigate a poor heating situation on another home. This one was a geothermal retrofit that had already gone through much of last winter with great results. Now they can’t heat some of the second floors? Why? I checked out the units and they were running fine. I went up into the attic and found that an electrician had been up here only two weeks ago to run some new wiring. The R-38 insulation was all piled to the side and much of the ceiling sheetrock was exposed.

I can’t heat a house properly with such obvious thermal leaks. If the envelope is compromised, it needs to be fixed regardless of the heat source.

The question is when do we consider geothermal? My answer is after all reasonably cost-effective conservation measures have been taken. If we can take a home that requires 75,000 BTUs to heat, and knock that load down to 50,000 BTUs through conservation measures, it not only reduces the operating costs but also reduces the installed cost of a geo system. Equipment size, well depths, operating costs, and installed costs all go down.

Most often, the reduction in the installed cost of the geothermal system offsets the cost of the insulation measures. In the above case, a six-ton geo system would have considerable savings for the home with no improvements to the insulation. However, a right sized four-ton unit would cost much less to both 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 geothermal system for the job. I sell and install geothermal systems for a living, but insulation and air sealing come first. After we’ve done everything we can cost-effectively do about heat loss, then we can talk about geothermal.

For a more in-depth look at insulation, check out our blog post on "The Power of Heat Loss"

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