Now I’m not suggesting that we as contractors should go to the warehouse and throw away all of our gas furnaces and electric air handlers. But, as up-to-date, forward-thinking contractors, we need to have a solid basic knowledge of geothermal systems and how they work. Even more importantly, I feel geothermal should be a part of your repertoire of equipment.
Obviously, there are some installations where a standard gas furnace is appropriate, where a high-efficiency gas furnace is correct, and even some where the customer will be best served with a geothermal system. The point of my message today is to make sure that you are as well-versed on geothermal as you are on gas and electric furnaces.
Get in the Loop
In our area, we typically perform vertical-loop installations, although we have done some horizontal loops and one pond loop. When we begin discussions with potential geothermal customers, we explain the many installation options so that they are aware of the process.
I believe that contractors, in general, are not making the public aware of the following numbers, which are the general rules for designing a geothermal system. Each ton of air conditioning requires one approximately 150-foot vertical loop. The hole that is drilled is typically 6 inches in diameter and the pre-made loop is dropped into the hole and then backfilled or grouted with bentonite in order to ensure proper heat transfer between the ground and the loop. The holes should not be closer than about 10 feet apart. With these numbers in mind, you can see that a home with a 5-ton cooling load would require five holes, and the drilling pattern needs to be done in 10-foot intervals.
The vertical loops are usually stopped about 5 feet below grade. The loops are then put together in a manifold and are run into the home. The number and location of the manifolds depends upon the yard configuration, the number of holes required, and the locations where the manifolds can be brought into the home. In our area, most homes that are potential candidates for a geothermal installation have a finished lower level so some definite thought must be used in designing where and how the manifolded system will enter the building. Another thing to remember is that the vertical loops do not usually have to be accessed after installation. Therefore, they may be put under driveways, patios, etc. One commercial building we did had no ground that wasn’t building or parking lot, so the loops all went in under the parking lot.
In talking about geothermal systems, it is important to be aware of the advantages. There is no doubt that in most cases, the initial upfront installation cost of a geothermal system is going to be greater than the cost of a conventional system. However, remember, not everyone is looking for the least expensive system on the market.
There is a 30 percent tax credit on the entire cost of the HVAC installation which is available to the homeowner. While this doesn’t typically cover the entire cost difference, it significantly narrows the gap. We have found that if a geothermal system is installed in a new home, using the 30 percent tax credit, given today’s mortgage rates and factoring in the savings in operating costs, the geothermal system actually provides a monthly cash savings.
There are several other benefits to homeowners which may not be obvious. The one that has probably sold the most installations for us is the fact that there are no outdoor air conditioning units. This is extremely important to someone with four, five, or more zones.
The placement of the indoor units is much more flexible with geothermal air handling units. Since there is no need for flues to be run to the exterior, the air handling units can be placed without regard to what is immediately above them. This provides a great deal of flexibility with regard to getting the air handlers in the best location to properly condition the home. Just the mere fact that there are no flues poking through the roof or sidewalls is a large benefit to many homeowners.
As I said earlier, don’t throw out your conventional equipment, but do make sure you are aware of the advantages that geothermal systems can bring to you and
Publication date: 10/21/2013