How to heat: Experts weigh in on heat pumps

Date Published: Mar 07 2011

What are the differences between air-source heat pumps and ground-source heat pumps? — Angie's List member Mark Schinman, Stanwood, Wash.

"An air-source heat pump is like an A/C that can go in reverse," says Luke Heiar, co-owner of highly rated Harker Heating & Cooling in Madison, Wis. It uses the difference between indoor and outdoor temperatures, cooling by drawing heat out of a home and warming by condensing and pumping heat from the air into a home.

A ground-source pump - also known as geothermal - uses the same principles, but uses the ground's stable temperatures to heat and cool. "Ground-source pumps, in most applications, are the more efficient of the two," says Chris Wierzbicki of highly rated Nutmeg Mechanical Services Inc. in Manchester, Conn.

However, an air-source heat pump is cheaper to install, Heiar says. They're more commonly used in moderate climates since harsh winter temperatures can negate the pump's efficiency.

Richard Henderson, president of highly rated M. B. Kiser Heating & Air Conditioning in Dallas, advises adding a gas-fired backup furnace to an air-source system. "It's much more cost effective than electric heat," he says.

Since geothermal pumps require significant excavation, installation costs are higher, but the systems are generally more durable. Heiar estimates installation costs for an air-source heat pump at $4,000 to $10,000. Geothermal can cost from $10,000 to $30,000, but a federal tax credit available until 2016 may offset that by up to 30 percent.

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Permalink Submitted by Crandaddy on Tue, 2012-02-07 14:10

I'd love to be able to do a geo thermal system for $30k, but so far that's not proven realistic. The only estimate I have received so far is in excess of $60k, which will not pay for itself for over 18 years.

Permalink Submitted by SomeGuy on Tue, 2012-02-07 14:10

Wow. If that's the estimate you are getting then I think you should look hard at the quotes. $60k is WAY too much. Where are you, New Jersey? We had 4 estimates that ranged from $28k to $42k which is about what they should be. The lower end is usually horizontal loops (i.e. digging in your yard w/ backhoe) and the higher ones vertical. That just seems way high but I also dont know your requirements (how many units, sq ft, etc.)

Permalink Submitted by misty on Tue, 2012-02-07 14:10

One of the most expensive part of a geo install is the excavation. Ask your contractor what options you have for this. More and more innovative methods are being developed. Just Ask!

Permalink Submitted by kirkj68 on Tue, 2012-02-07 14:10

Can a gas fired backup furnace be "added" to an existing air source heat pump, currently with electric backup, or must one start from scratch with a new system?

Permalink Submitted by Peggy on Tue, 2012-02-07 14:10

Can an air source AC/heat pump be added to a gas steam boiler heated house? Would this be an energy & cost efficient way to go for cooling, if not providing some heating, in the Northeast?

Permalink Submitted by Global Hemp on Tue, 2012-02-07 14:10

Ground source "geothermal" heat pumps can also be installed into a pond if the conditions are sufficient. Check out the WaterFurnace.com website to see illustrations. As for excavation, that depends on your area and soil type (e.g., rocky). You can have either "wells" or "trench." Wells go straight down and a trench is horizontal. In the case of a trench, you need to make sure plant roots are not going to interfere -- now and the future. Ground source heat pumps have a Coefficient of Performance (COP) of 5. A "high efficiency" natural gas furnace has an efficiency of 90% of more. Therefore its COP is 0.9 which means that 10% of the energy (natural gas) is lost, goes up chimney without heating house. Now, a geothermal heat pump is 500% efficient -- since you are getting the heat from ground (Earth) which is stored solar heat. Therefore, you are paying to run the system, which gets "free" energy from the ground -- something you don't have to pay for. So, geothermal is 500% efficient compared to at most 95-97% efficient furnaces. For eco warriors, they can look into even going beyond with solar assisted geothermal (heat pipes on roof) as well as ventilation exchange controller. Efficiencies can go as high at 1,000%. That means for each unit of energy that is input (e.g., electrical or natural gas), 10 units of energy are returned!

Permalink Submitted by John on Tue, 2012-02-07 14:10

I had a geothermal system installed in 2004. The external tubing was laid out horizontally. The cost was about $12000. It works beautifully for our 3000 square foot house.

Permalink Submitted by Mark on Tue, 2012-02-07 14:10

Yes, heat pumps can be added to a gas furnace or boiler in most scenarios. You'll get better equipment & efficiencies with an all new system that has better communication abilities (thermostats play a big part these days). But you can add a basic heat pump to an old furnace and typically see immediate benefits. Geothermal installation costs totally vary with what corner of the country you're in as well and are as much a factor of cost of living as ground conditions. Geothermal heat pump equipment is more expensive than an air source heat pump but has DOUBLE the life expectancy. And nobody's mentioned the savings you gain with a geothermal heat pump's ability to help heat your domestic hot water, there's another 30% - 50% savings that's more or less free!

Permalink Submitted by geo man dan on Tue, 2012-02-07 14:10

We had geothermal installed last year for 18k, but got a 1k state rebate and also a 30% fed tax deduction bringing the total to around 12k. No messy trenches in the yard either, they did it with horizontal borings, a very cool operation. A very efficient system and expecting the savings to pay it off in 10 years or less. We no longer have a natural gas bill, what a relief, I hated the "delivery and services" charge on the gas bill.

Permalink Submitted by Tim Funke on Tue, 2012-02-07 14:10

OK before I start, I need to state that I am NOT against ground source HPs. I just think they are grossly oversold for what they provide. When it is zero outside a ground source hp will be more efficient, when it is 30,40,50 outside, then an air source is more efficient. So you have to look at the heating hours in the different temperature bins. In Mo. we have 150 or so hours below 15 degrees and many times more in the higher range. I replace my ground source with an air source and had my heating and cooling cost (which are metered separately) go down. Also, look up the cost of an extended warranty on a ground source (which will not cover the circulator pump or the loop) and you will find that the extended warranty cost twice as much as for an air source.

Permalink Submitted by Tim Funke on Tue, 2012-02-07 14:10

You also need to do an analysis of your local utility. In our market, gas is higher than the backup strip heat and the install cost is higher. If this is the only appliance in your home on gas, then you wind up paying the $16 to $20 meter fee every month to use the auxiliary heat for 2 weeks out of the year.

Permalink Submitted by dhamilton on Tue, 2012-02-07 14:10

We install geothermal all the time. In eastern Massachusetts, we have to install vertical bore loops which are expensive. With inverter technology in air to air heatpumps, they now can make air to air heat pumps close to the efficiency of geothermal without the huge costs.

Permalink Submitted by Glad R. on Tue, 2012-02-07 14:10

My basement is cold all winter even when the temperature upstairs is 70 degrees. What can I do to get it to warm up besides letting the boiler working all day? Thanks.

Permalink Submitted by Harold on Tue, 2012-02-07 14:10

I would be very wary of considering a heat pump. First off, it depends on the other fuel you have. I use propane that is cheaper than natural gas. The air-to-air heat pumps use electricity and even if you get a special rate, it is questionable as to if you will ever actually recover costs. Your electric use will still rise and you will still need to burn the other fuel. The electric company skews their numbers when they give you a comparison – they priced propane at 60 cents higher a gallon that what it was selling for to make their case. The A/C company skewed their numbers by creating a home model that used 300 gallons more propane per year than we use. Fortunately I’ve tracked our utility usage and costs for the past six years and had actual numbers. Electric rates will always rise – they will never go down. Propane shifts with the market and has dropped in cost as many times as it has risen and I can lock in propane rates each year in May when they are at their lowest. If your winter temps ever get below 30 degrees you will need a duel heat system, and to actually feel comfortable you will find yourself setting your thermostat higher burning both fuels – heat pumps heat you home with air at the temperature you set – 70 degree setting gives you 70 degree air – feels like your AC is running instead of a furnace. Maybe geothermal is better, but have fun paying the $20K to install it. I've done the numbers and it doesn't work for my house.

Permalink Submitted by Ches on Tue, 2012-02-07 14:10

It's all about the insulation, not the heating. Insulated well and you save money, not and you pay. Insulated Windows, Walls Attic, Basement Ceiling, (or Floor). What ever the case may be. The heater will only heat as well as the house will hold the heat. And wrap your return vent if you have electric heat.