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Heat pump/Furnace size

Posted by Searcher99 (My Page) on
Sun, Jul 22, 12 at 12:50

We recently purchased a Bryant 289 two-stage heat pump and a plus 80 model 315 furnace instead of a more efficient furnace and A/C. While the heat pump was pricey, we did receive 2 rebates The theory is that the larger heat pump will do most of the work year round, while the 80% furnace will only kick in as needed. Since I am at home most of the time, we were told not to touch the thermostat day or night as this would just "confuse" the heat pump. And I have been told to run the furnace fan on low year round to circulate the air. Is this a sound philosophy? I'm not doubting my dealer. I just want to make sure I understand the principal.
Also we live in a condominium in Nebraska with 1742 square feet upstairs(where we spend 95% of our time) and 420 square feet in the basement. I've been told by other parties that these two units are too large for this space. Is that true?


Follow-Up Postings:

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RE: Heat pump/Furnace size

What are the sizes of the furnace and heat pump? What thermostat do you have?

Your contractor should have done a heating and cooling calculation to determine the sizes. Do you recall the sizes of your old equipment?

I am not sure I agree with the contractor about confusing the heat pump if you were to set back temperature. If you had electrical strips instead a furnace as the heat source back up, then I agree the set back should be small (3-4) degrees. However if you have a back up gas furnace, then I would think the furnace would take over and warm up the house from a large set back (5 - 8 degrees). It becomes a matter of how the thermostat is set up to operate in these conditions.

Setting the fan on low during the winter helps even out the house temperature. You can also do this in summer, but it may cause the humidity level to increase.


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RE: Heat pump/Furnace size

Heat pumps are not smart enough to get confused. Thermostats, on the other hand...

For doing heat pump setbacks, you need a thermostat 'smart' enough to know when to activate the heat pump so that the auxillary heat does not active when recovering from the setback.


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RE: Heat pump/Furnace size

My heat pump is 3 ton 36,000 BTU. Furnace is 90,000 BTU with 4 ton blower. Thermostat is Bryant Evolution control. I also have an Aprilaire air cleaner. Your advice is appreciated.


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RE: Heat pump/Furnace size

The Bryant Evolution controller is a very good thermostat. I am confident it will not be confused controlling the furnace and heat pump in various indoor and outdoor temperature scenarios.

I believe the controller can be programmed to have two outdoor lock out temperatures. Above one temperature (ex. 40 degrees) only the heat pump will operate, and below a second temperature (ex. 20), only the furnace will operate. In between these temperature the controller will first use the heat pump to warm the house, and then switch to the furnace as needed.

Ask the HVAC contractor what he has done to set up the controller. It would be a shame not to use temperature set backs with your set up.


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RE: Heat pump/Furnace size

Thanks for the advice Mike. Just in hind sight did I purchase a system that is too large for my living space?


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RE: Heat pump/Furnace size

Oversized on the furnace.

Dealer should be taken to woodshed!

IMO


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RE: Heat pump/Furnace size

Based on area it seems large. What are the typical highs and lows in the summer and winter?


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RE: Heat pump/Furnace size

January Hi-35 lo-14
July Hi-89 lo-67
Average


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RE: Heat pump/Furnace size

Month Low High
Jan 11.5�F 33.2�F
Feb 17.2�F 39.3�F
Mar 27.5�F 51.2�F
Apr 38.8�F 63.5�F
May 50.1�F 73.8�F
Jun 60.4�F 84.9�F
Jul 65.9�F 89.6�F
Aug 63.7�F 87.1�F
Sept 53.2�F 78.8�F
Oct 40.4�F 66.5�F
Nov 27.0�F 49.1�F
Dec 16.2�F 36.8�F


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RE: Heat pump/Furnace size

If the average low in January is 14 degrees F, then I assume you will see zero degree temperatures in the winter. The next size smaller for the furnace is 70,000 BTU, which translates to a 56,000 BTU output. It may be sufficient for your condo, but it is hard to tell.

You have a two-stage furnace, so it should not short cycle even it is a little over sized. Hopefully your duct work is sized correctly for this size furnace.


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