Is it possible to reduce your energy bill and carbon dioxide emissions and get air conditioning for a home that didn't have it, all at the same time?

Sometimes it is. Changing your home's climate control system to a heat pump, from the typical Washington combination of a gas furnace or electric resistance units and no air conditioner, may reduce your energy costs significantly even though doing this adds air conditioning. You are likely to save more energy during the heating season while the system is heating, than you'll use during the short northwestern cooling season while the system is running in the air conditioning direction. Cost assistance may be available from PSE's energy efficiency rebate program and/or federal tax credits.

A heat pump is an energy efficient combined heater and air conditioner. Think of it as a very efficient air conditioner with a reversing valve which enables heat to flow in two directions, instead of just one. This simple idea makes it possible to use the same system for both heating and air conditioning, instead of having separate furnaces and air conditioners.

Heat pumps are energy efficient because the physics on which their design is based enables them to capture thermal energy from the outside environment. Most of the heating or cooling energy comes from the outside air, ground or water. This greatly reduces the amount of energy you need to buy to change the temperature in your house. I will explain briefly at the end.

Heat pumps are a proven technology. They evolved from the conventional air conditioning systems which have been in use for decades. They are made for buildings with HVAC system ducts and as through-the-wall units for buildings without ducts. New heat pumps are readily available from many local heating system contractors. Most homes don't have heat pumps yet, simply because people usually don't replace their furnace till the furnace stops working.

Heat pumps work best in a climate like ours, where outside temperatures are usually above freezing in the winter. Your heat pump will need a supplemental form of heat for cold days, although that supplemental heater usually won't run. Heat pumps are available with supplemental gas or electric heat. In this climate, electric supplemental heat will be more common.

Heat pumps significantly reduce the carbon footprint of your climate control system. They use less energy than old systems. As PSE eliminates coal power over the next few years, local heat pump carbon footprints will fall further. Some of the energy they use and will use is electricity generated from renewable sources.

How it works: A heat pump uses electricity to compress a gas into a liquid, and then captures thermal energy from the phase change that occurs when the pressure is released and the liquid changes back into a gas. The electric energy required to run the compressor is less than the heat energy released during the phase change. It is far less than the energy required to heat the building with resistance heaters or fueled furnaces.

Typical heat pumps are "air-source." They reject excess heat into the air. A ground-source (geothermal) heat pump can be coupled with water or the ground instead of air. Geothermal heat pumps are even more efficient, but are more expensive to install.