Business case for geothermal

[SolarAndWood]

I recently discovered that I have a well 20' from the house. Does this discovery and the 30% tax incentive materially change the business case for geothermal? I dismissed geothermal 6 years ago because of the cost of a system using horizontal trenches in the lawn. Is a 5" cast iron pipe big enough to get a heat exchanger down?

 

[jimbom]

Five inch should be big enough. It would seem to me to depend on the depth of the well, the groundwater, and the load.

 

[SolarAndWood]

I assume I can simply unbolt the hand pump and drop a bob in to determine depth? What is the groundwater variable? Making sure it won't rot the heat exchanger or how big the aquifer is for heat transfer?

 

[jimbom]

The plumb bob should work. The depth of the water over the bottom of the well is important.

 

[Highbeam]

Water depth is important because it tells you how much water is in the hole to cover more heat exchanger area. More water is gooder, means you can have more surface area exposed to cold water.

Of course, you could do the kind of system where you draw well water, steal the heat, and dump it into a pond if the well is a good producer. What do they call that? Open loop?

 

[mbcijim]

When I built my home in 2009, the tax credit for geothermal almost exactly worked out to the cost over air source heat pump. Simply, the 30% tax credit was equal to the cost of the ground trenching/pipe and all associated outdoor work.

So if air source heat pump is your #2 choice, then yes, go for geothermal, at least based on my experience.

 

[hemlock]

Would one well give you enough "heat"? Generally, a ground source geothermal system has more than one well. If you go with the "open loop", or "pump and dump", make sure the well can keep up.

 

[SolarAndWood]

My uneducated guess is I have a lot more heat load than well. However, with zoned distribution, I am thinking I could heat the remote parts of the house with it to compliment the central stove instead of going the boiler route. It might be enough to keep the house from freezing while we are away and available for the few weeks a year we air condition. I am looking at it as part of the mix if I can keep the cost under control as opposed to the silver bullet.