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Heat Pump Water Heater vs. Marathon w/ Geothermal Heating/Cooling

Posted by dboyer76 (My Page) on
Tue, Dec 13, 11 at 22:59

We are building a new house and I am trying to decide wether to go with a HPWH or an electric Marathon. Our house will have two Trane T2GY units that will provide heated water to the water heaters (2, 80 gal.). We live in Northern Michigan and the units will be in the basement. I am wondering if anyone has an opinion on the pros and cons. I realize that the HPWH's draw heat from the basement which will be heated by in floor heat but is it significant? Will the dehumidifying effect of the HPWH save more energy than the "extra" heating we may have to do in the basement (by not using our dehumidifier as much)? And, I believe I read that the energy use of a HPWH is a third as much so the payback period may be faster vs. the Marathon? I realize I am probably splitting hairs but want to try to be as efficient as possible. Any opinions or experiences would be appreciated!


Follow-Up Postings:

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RE: Heat Pump Water Heater vs. Marathon w/ Geothermal Heating/Coo

i think hpwh are better used in warm climate where there is a lot of cooling going on.


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RE: Heat Pump Water Heater vs. Marathon w/ Geothermal Heating/Coo

"I realize that the HPWH's draw heat from the basement which will be heated by in floor heat but is it significant?"

I have a heat pump hot water heater in my basement here in Maryland. The heat pump has no measurable effect on basement temperature, however it does serve to reduce the basement relative humidity 3-5%.

The walls of your basement serve as a massive heat sink and changing the room temperature of your basement by operating a relatively small "air conditioner" isn't going to happen. (If your hot water heat pump were installed in an upstairs utility closet, the cooling might be an issue.)

In the limiting case of you actually not using any hot water, for example, any heat energy extracted from the basement air mass would be transferred to the heated water sitting in the tank. In the steady state, there would be as much heat being transferred back into the air mass as would be extracted from it.

A heat imbalance is created when you use hot water and the heat is lost from the basement system via the heated water going to the sinks and the cold water entering the tank to replace it.

My family of two saves about $50 per month compared to my old electric hot water heater. Also, there are frequently tax credits or rebates available.


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