Comparing geothermal to ultra high efficiency conventional

marrtNovember 3, 2011

I'm going through the exercise of comparing geothermal to conventional. Here are the details:

Location: Northern Virginia

Propane rate: $2.55/gallon

Electric rate: $.115 per kilowatt hour

Geothermal: After rebates/tax credits, the geothermal system is about $23,000 installed for two WaterFurnace 3 ton two-stage units with electric auxiliary heaters. One unit includes a desuperheater to help with hot water.

Conventional: The conventional units are Carrier Infinity 20 Seer heat pumps with a 95% efficiency propane furnace for auxiliary heat. Installed price after rebates is about $17,000.

To my amazement, there's no place online where I can compare the payback of these two systems. Conventional wisdom suggests the geothermal system is the way to go. But my HVAC guy is saying the conventional system will be just as efficient for $6K less. Thoughts?

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At that price, I'd probably do geo. The big advantage is that you system will last longer.

It is not that easy to compare HE with geo which is why you don't find an online comparison. My personal guess is that you are within 10% of each other in the summer and 20% less with geo in the winter. So if your house is tight, this might just be $200 a year so the payback for geo is 30 years. But - and this is a big but - the geo unit will last twice as long so as soon as you have to replace a unit (15? years), then geo comes out ahead.

People may disagree but I live in NC - a bit warmer than you - have 16 seer HPs (with NG backup) and spend roughly $700 a year to heat 5000 sqft. If I had propane, it would be $850. So that is where 20% really isn't a lot of money ($170 to be exact). I spend about $700 to a/c so another $70 for summer. You see why the payback is so long.....

Now the desuperheater may tip the balance. I have no idea what that saves but it could be $300 a year. That would shorten payback significantly (obviously). Or you could go solar for $3k (at least with my tax credits) and save yourself $400 a year.....

    Bookmark   November 3, 2011 at 7:52PM
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David Cary pretty much said it all. I would go either with an all-electric Carrier Infinity GreenSpeed system or geothermal and be happy with either choice - if properly installed!

$23k for 2-3ton systems is MOST reasonable. However, there are no details of the ground loop system.

I would install the desuperheater on both HPs, that way you will be producing DHW whichever HP is running.


    Bookmark   November 4, 2011 at 3:10PM
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This is new home construction?

I personally would weigh geothermal with the Fed Govt tax credit versus Carrier's new Greenspeed HP-no credit. Forget the propane for backup.


    Bookmark   November 4, 2011 at 3:29PM
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