Using existing 1970 galvanized (furnace) ductwork for heat pump.
chrislene
| Posted in General Questions on
Hi,
Can someone please opine on switching out furnaces or AC for heat pumps while utilizing existing ductwork? We have a small house in MD and will keep the gas furnace but replace the AC with a heat pump. They both use the existing galvanized ductwork. We will then have options for heating depending on price of gas vs electricity. I am concerned that the HP which has less forceful air flow might not operate efficiently with larger 1970 duct installation.Â
Thanks
A
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Replies
Your assumptions are likely correct, but the only way to know is to have an engineer review what you have and compare it to what a ducted heat pump would require.
Yes, I investigated that route and was quoted $1,800 for the service. The house is 1000 sq ft above ground and same below. Do you know any engineers who might charge less. I do not even understand how the discussion to replace systems with HP are taking place without highlighting that they may require total duct replacement as well. It is misleading. Thanks
Wait, so you're keeping your original furnace, which houses the fan correct? You're only switching the condensing unit, that houses the compressor and refrigerant valves, and possibly switching out the evaporator coils that sit above the furnace and currently cool but will soon heat and cool the air?
There should be no real change in your systems operations with regards to airflow. Before the switch you have a gas furnace with a blower that blows across the furnace and then the evaporator coils. After you switch you'll have a gas furnace that blows across the furnace and then the evaporator coils. You might want to make sure the new evaporator coils have a similar amount of pressure drop across them as the old ones (if they even get changed out) and if you replace the furnace you might make sure that the new furnace has as powerful of a fan as the old furnace to ensure the airflow remains the same.
Am I missing something?
Maybe I am misunderstanding something. With this furnace, I have an exterior AC condensing unit. I thought I could replace the exterior condensing unit with a heat pump which could work with the same ductwork. Are you saying that the HP air gets blown thru the existing ducts by the existing furnace mechanism? Thanks
Yes. Your blower is likely a part of your furnace and the AC portion is just a set of evaporator coils that sits on top of the furnace. You should check with a local installer to see if you can reuse the evaporator coils and refrigerant tubing and just replace your condensing unit. So, if that is your setup, then you should have no problem just reusing the system as it is and replacing your A/C only condensing unit with a heat pump type but you may need to make some modifications inside at the evaporator coils as well but someone will need to do some investigating to figure all that out.
Long story short, your ductwork should be fine if you change from an A/C to heat pump setup. Your refrigerant lines, coils, condensing unit, etc, all that may or may not need to be changed out though.