Heat pumps and fan speeds

Old 10-03-09, 11:47 AM
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Heat pumps and fan speeds

I've had a heat pump connected to a forced air electric furnace for a few years now. The house is heated great but the heat pump still cycles often and with this happening the fan in the furnace is noisy and irritating. When I had just the forced air my fan motor was set to low and medium speed. When the heat pump was installed the furnace fan was wired to high speed causing greater air flow and more noise. Is it possible that the higher speed is too much; cooling the heat from the heat pump causing my pump to cycle too often. Lowering the speed would lower the noise and circulate the air better. Could this be possible?
Old 10-03-09, 03:26 PM
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You indoor coil needs minimum air flow (CFM) in both cooling and heating mode. If you lower it below the required CFM you run the risk of freezing the coil in cooling mode, and reducing efficiency in heat mode. The only way to know for sure is to have a pro measure the static pressure and see if lower the fan speed is safe. Annoying noises from fans is also often due to ductwork that is in need of remediation due to too high static pressure.
Find a pro that is well versed in ductwork problem diagnosis.
Old 10-03-09, 06:34 PM
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What is the make and model # on both indoor and outdoor unit.

Highest fan speed may not be needed if all the specs are in line of what the install gude calls for.
Old 10-07-09, 07:44 AM
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FWIW, I just had two heat pumps upgraded, and the new variable speed air handlers made it like a hurricane in my office!

I have to say, the outfit that did the installation was great, they came back and at no charge redid the ductwork for the whole three room office area. They added ducts, increased the size of a couple of others, and also replaced the whole plenum with a properly sized one for the system. They also replaced all the grills with a newer type with better airflow.

I know they should have "designed it properly" in the first place, but having them fix it without a hint of wanting me to pay for the extra work was pleasent, I was bracing for a fight.

Without a doubt, you need to pick the contractor carefully that you use for your installation. Although this guy was $1500 more for the two installations, the end result was I got what I paid for. I'm sure the low cost bid would have ended up growing when the system was installed and we had the airflow issues.

FWIW, my units were Amana (Goodman), and you can program the variable speed air handlers to a limited degree for more or less airflow. I believe it's 10% more and 15% less.

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