Geothermal Retrofit

Q: Is it feasible to do a geothermal retrofit?

A: Sometimes it is…sometimes not.

If you’re gutting the house, a geo retrofit is as simple as a new installation. If you’re not, read on…

The primary goal is to reduce the load. This means upgrading windows and insulation first. These costs will translate into a significantly smaller geo system which will then pay for them and save more energy than geo alone. An unimproved house with a geo system will cause the geo system to be overloaded. Remember, the primary goal is to reduce the load.

The subject should then be broken down into 2 parts.
1) Do you have forced air heating with ductwork?
2) Do you have hot water heating with baseboards, radiators or radiant floors? This is called hydronic heating.

If you have forced air heating and it currently uses electricity or gas or oil, then generally the ductwork is too small and needs to be upgraded. The reason being is that the “dead dinosaur” burning furnace would deliver heat at 140 deg F and the new heat pump system would deliver only 100 deg F. (all approx values) This requires bigger ductwork to deliver the same amount of total heat. Simple, right?

An exception might be a really old house that had a big heating system designed for single pane glass and no insulation. If the glass and insulation were upgraded then the originally large ductwork would now be adequately sized. However this house would likely have been renovated at some point and the heating system could be inadequate or dysfunctional. If the basement is unfinished then ductwork upgrades are simpler than if the basement is fully finished, blocking access to the ductwork.

If you are replacing a tired air-source heat pump then the ductwork will likely be adequate.

If you have hydronic heating and it currently uses baseboard radiators that have copper tubes and aluminum fins (they’re not radiators at all, they’re convectors) then you’re out of luck unless you replace them and probably the distribution piping too.

If you have baseboard radiators that have cast-iron fins (rare) you may be in luck except you’d probably have to add more of them to make up for the previously mentioned lower output temperatures. If you have cast iron radiators (really old school) they may work but you may need to add more of them. They’ll need to be flushed and maybe some piping upgraded too.

If you have radiant floors, they are the easiest to convert, except some older floors (and still today) were/are badly designed and installed. They required high operating temps and were not that comfortable to begin with. If the radiant floors have enough tubing and loops installed the conversion should be relatively simple.

The 2 best parts of hydronic heating conversions is that you can rip out the mixing valve that used to mix down the high “dead dinosaur” burning boiler temps to what the radiant floor requires. You can also rip out the evil chimney and the CO detector. This was so inefficient due to the high temp standby losses in the mechanical room. Geo systems operate at low temps and have little or no standby losses.

The other best thing with hydronic heating conversions is that you can install outdoor reset control. http://www.tekmarcontrols.com/literature/acrobat/p022.pdf This is a further energy saving control that has been around for more than 40 years but only works on hydronic heating. At exchangenergy we install it on every hydronic system we design.

Summing up, geo retrofits can be feasible and even have a shorter payback than a new installation if you are replacing oil or propane as the fuel source. If your home meets the above criteria then a site visit is the next step.