It is less expensive to install because it does not require any gas plumbing, and it contains both heating and air conditioning in one unit. It can be pretty efficient under the right conditions, and that is its selling point, but it is really inefficient when the back up kicks in.

Thank you Joe and Mike. It just seems a system like this would be better suited for warmer climates than the Philly suburbs. I am basing this on currently living in Central NJ, and while the winters have been warmer, there are still many days/nights that are lower than 30 or 40 degrees, which is when I have read these systems would use the back-up. I wonder why a newer home would install this type of system in a colder climate...is it cheaper to install?

Hi Soulwindows!

Mike's answer is a good one. I'd just like to add a little more in case it helps your understanding. The back up system kicks in only when the heat pump needs to make up a big temperature difference (between the current temperature, and the temperature you want it to be). This happens most often when temperatures outide get really low (like 20 degrees or lower) or you turn the thermostat way up. The heat pump "knows" it has to produce a lot of heat to get to your desired temp, so it engages the back up system (think of it like a big toaster). It is VERY inefficient when the back up is running, but very efficient under normal circumstances.

It might help to know that the back up system will automatically kick into action whn you turn the thermostat up more than 3 degrees above the existing temp in the home. For this reason, it is recommended to keep the thermostat a relatively steady, but comfortable setting - as opposed to turning it way down, then spiking it up when you get home from work, for example.

Hope that helps. Here are 3 good sites (mostly about energy saving tips) for info that should provide more complete and (hopefully) useful info:
http://home.howstuffworks.com/home-improvement/heating-and-c…
http://www1.eere.energy.gov/consumer/tips/heat_pumps.html
http://www.doityourself.com/stry/heatpumpenergyuse

Hope that helps!

A heat pump is a refrigerated air-conditioner with the ability to be operated in reverse to heat the home. The electric back up is needed because the heat pump will heat the home more gradually than we sometimes desire. It consists of electric elements which heat up and have air blowing across them to heat the house. The electric back up heat is not very effecient and will cost more to operate if you use that feature. The heat pump is considered efficient, but gas fired heat is usually less expensive to operate.

One advantage of the heat pump is that you have one single unit to heat and cool the house. It is a unit which can be expensive to repair or replace.

Personally, I don't care much for them. There are many heat-air contractors who swear by them though.

Hope this helps!