I installed a ground source heat pump in my home near Baltimore, MD. I am not an expert on the subject, but can speak of my own experiences with the technology. I made the switch over from natural gas a couple of years ago after hearing that ground source heat pumps are one of the greenest and least expensive ways to heat and cool a space. If you're deciding whether this technology makes sense for you, one of your first considerations is the difference in the expected remaining service life between your current heating unit and your cooling unit. If you have, say, a 20-year old furnace for heating, and a separate outdoor A/C unit that is brand new, then know that you would be throwing away that brand new A/C unit since the ground source heat pump is used for both heating and cooling. In my case, both my furnace and A/C units were old, so for me this was not a concern.
As you probably know, the system consists mainly of an indoor unit housing a blower and a compressor, and a ground loop buried in the yard. There is usually the option of adding a desuperheater, which is essentially a device that heats your water using the excess heat from the heat pump, giving you free hot water in the summer. In my case, the installer decided to install an additional hot water tank for this purpose, allowing me to keep my existing almost new water heater and leaving me with two water tanks and little chance that I would run out of hot water if my wife and I decided to take separate simultaneous showers. Also, with ground source heat pumps, there is no outdoor unit, one of the benefits of which is a quiet backyard--good for summer gatherings on the deck or patio. The indoor unit was roughly the same size as my old gas furnace, which allowed for an in place swap out. It also happened to be in the most convenient possible location, just inside the front wall of the house, allowing easy access to the ground loop buried in the front yard.
Inside, when the unit is running, you CAN hear it, which was probably my biggest surprise and disappointment with my new heat pump. It comes mainly from the whooshing sound of the air being pushed through the ducts. There ARE measures one can take to mitigate this. A properly installed dual stage heat pump will run on a low fan speed much of the time, which translates to quieter operation. A dual stage model also happens to be more efficient and comfortable, helping to ease temperature variations between rooms. In retrospect, I should have spent the extra couple thousand dollars for dual stage. There are also duct mods you can make. Perhaps the most cost effective is insulating the first 4 feet of duct on both the supply and return side, or replacing it with flex duct. It is best to take care of this while the installers are in there anyway replacing the unit. Also, you will want to ask your installer if your existing ducts, if you have them, are sized properly. Apparently, if you have narrow ducts, that can strain the system. I was told that my ducts did not have this problem. If you do have to replace your ducts, go with insulated ducts to further reduce the noise and improve efficiency.
On to the ground loop. The ground loop can be installed horizontally or vertically. When possible, horizontal is usually preferred as it costs about half as much to excavate. My installer went with vertical since I have a modest yard size with many trees and other landscaping obstacles.
I went with a company called Dynatemp on a recommendation from a colleague. They performed the unit installation and contracted the ground loop excavation to another company called Easterday. The drillers installed a vertical loop for a 4 ton system, 30 feet from the house, and 600 feet deep, at a cost of $14000. They installed a Climatemaster Tranquility 20 for the indoor unit at a cost of $14000, making the total cost of the project--before tax breaks--about $28000. To be sure, that is a hefty price tag, but with tax breaks at the federal, state, and local level, I received almost half of that back, making the grand total for me somewhere in the range of $15000. I do not know what kind of credits are running nowadays, and there are some restrictions, so it pays to do your homework before you sign up to ensure that the unit you are installing will be eligible for all the tax credits you expect to get. Also, after the installation is complete, there is some paperwork to file, so be sure to follow the instructions closely and save all your receipts. Finally, with any new technology like this where a handful of companies hold a monopoly, there is always the possibility of price gouging. For a big investment like this, I would get 2 or 3 estimates even if you think you're getting a good deal.
The unit for me has been maintenance free. The only routine maintenance I do is to replace the air filter twice a year. The filter is a non-standard size and probably won't be carried by the big box hardware stores, but I've had no difficulty finding it online at a reasonable price. The indoor unit is expected to last 20 years and the ground loop should outlive you and me.
I estimate the system has probably cut down my utility bill by about half. I have been hard pressed to come up with an exact figure as I still have an old electric wall unit in the addition behind my house. I was offered the option of replacing the wall unit with a new model that tied into the ground loop at an additional cost of $6000. Knowing that I could defer this until later and that I still had some years left in my old electric unit, I opted out. Currently, my summer utility bill is around $100 and in the winter it averages around $300/month due to my constantly running the electric unit in the addition. Though I haven't tried it, I suspect that if I turned off the heat in the addition my winter bill would be closer to $200/month. Again, the supposed payback period is highly variable and depends on many factors, so it is difficult to come up with an estimate. For a single family home it can range from a couple of years all the way up to a dozen or more years. It tends to be longer if you currently have natural gas heating and shorter if you have all electric heating. Also, while you're evaluating heat pump models, don't skimp on the thermostat. A higher end thermostat will allow you to fine tune more of the settings that will increase your comfort and decrease your energy usage.
In summary, I have been happy with my ground source heat pump, minus the high initial cost and the somewhat noisy operation. As mentioned, there are ways to mitigate the noise. The other less talked about benefit is that my home is more comfortable year round. Because the system is designed to put out air that is closer to the ambient temperature, the blower tends to run longer in each cycle, providing more even heat throughout the house and minimzing air pockets that cause drafts in one part of the house. I wholeheartedly recommend ground source heat pumps for anybody who is due for a replacement of both their heating and cooling units, especially if their heating unit is electric. In any case, take the first step and get an installer to come out and assess your property for geothermal suitability. For those with gas heat who do not make good geothermal candidates, know that the latest gas furnaces are quite efficient also.
