Wednesday, October 13, 2010

Heat pump qualification.

I have many customers ask me about their heat pumps. The questions often come from a lack of understanding of how they work. I am going to go through what may seem to be an oversimplified explaination of how a heat pump works. So here goes. The first thing that happens is there is a call for heat which means that the temperature has dropped to the point that the thermostat is "calling" for the heat to come on. This is what is called a first stage call for heat. At this point, depending upon the outside temperature the outdoor unit comes on in reverse of the air conditioner to bring the heat from the outside into the space. Now this is where the problem happens. Often a heat pump has no control on it to turn it off when it is too cold outside and the customer feels the "cold" air blowing on them. The air is not necessarily cold but is not very warm so it is referred to as cold. Because often there is nothing to stop the outdoor system from trying to heat even when there is not enough heat to be practical, the customer has to wait until the thermostat temperature falls 1 degree and at this point the backup heat is staged in. This is called a second stage call for heat. Depending upon the type of system you have the backup heat can be electric or gas. When this call happens, this is when the real heat begins to pour out of the register. Now for those of you who have no mechanism to shut off the heat pump when it gets too cold outside (That is a majority of people from what I have seen but not if you're one of my customers), you have a choice. At about 20 degrees outside, the heat pump is close to what is called it's balance point which simply means that it is using more energy to make heat than it is giving you. At that temperature and below you could simply go over to your themostat and turn it to emergency heat. There is a button on the thermostat that says exactly that. Just don't forget to turn it back to heat when the temperature gets above 20 degrees. Or you could have a professional come and install a new thermostat that can do that automatically. This is the way I now make all my systems operate. For those of you that are colder natured and have electric backup heat, we can also stage your backup heat in which simply means that at say 30 degrees we run not just the heat pump but one stage of electric heat to make the temperature warmer. Mind you this will cost you more to operate but it will make it run warmer. Just a note, when the electric backup heat comes on is when the meter really starts to spin so if you don't have to run that much, you will have a lower electric bill.
Now for those of you who have a hybrid which simply means that you have a gas furnace as your backup heat source, your system is a bit different in that you cannot stage this system on with the heat pump. These two systems never operate at the same time. Either the heat pump is on or the backup furnace is on. But you can and often will have a two stage gas furnace as your backup system. This means that the furnace does not come on at full at first. Most of the two stage furnaces come on at about 80% for first stage and then 100% at second. For us in Indiana, there are many days in the spring and fall that a heat pump is practical but in the winter, You will be using a lot of backup heat source. A hybrid system does qualify for the tax credit. If you have questions or would like to have an evaluation of your system for free, just give us a call.