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Old 01-14-2010, 08:57 PM   #1
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Heat Pumps


I understand that most heat pumps don't provide much (if any) heat when the outside temperature is 40 degrees F or below and most or all of our heat comes from the heat strips in the air handler. Does any heat pump manufacturer actually turn the compressor off when the temperature gets low or do they just allow the compressor to run and consume power?

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Old 01-14-2010, 09:28 PM   #2
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They do give heat below 40 deg. I run mine down to about 10 deg. They also can be shut off at whatever temp you want depending upon the type of system you have. IE: Dual fuel or all alectric

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Old 01-14-2010, 10:03 PM   #3
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Somebody told you a bunch of incorrect information czars. Heat pumps provide heat well below any temps Florida will ever see. They also do it at 1/2 to 1/4th of the cost of electric elements. When both run at the same time you have some heat from the elements (at a much higher cost per BTU) and some cheap heat at the same time.
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Old 01-21-2010, 06:36 PM   #4
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I have a 20 year old Bryant split-system Heat Pump with R22. I would like to replace it in the near future. My question is whether I need to replace both the outside Heat Pump unit (compressor /evaporator etc) as well as the interior unit with Fan-coil unit. The Fan-coil unit is in attic together with a supplementary electric heat system. Can I use the existing coil with a new unit using new refrigerants instead of the old R22?

I just changed the motor on the Fan-coil unit after 20 years of operation and expect that the compressor will probably give up in the next year. I would prefer to do just the outside unit as the access to the attic is too small for new unit. (I assume that the existing unit was installed before the house roof was closed).

Would love to hear some expert opinions.
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Old 01-21-2010, 06:55 PM   #5
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Mix and match will not work sam. You don't want a 20 year old coil to leak on a brand new heat pump. The old coil won't have the capacity needed for the new higher SEER heat pump. Oil from R22 systems and 410A systems don't mix and flushing is very expensive. Air handlers can be taken down to parts and reassembled in the attic if there's no way to make the access hole bigger. Around here an inspector will not pass that unless there is no other option so it's a last resort.
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Old 01-21-2010, 08:14 PM   #6
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Originally Posted by Sam_amaya View Post
I have a 20 year old Bryant split-system Heat Pump with R22. I would like to replace it in the near future. My question is whether I need to replace both the outside Heat Pump unit (compressor /evaporator etc) as well as the interior unit with Fan-coil unit. The Fan-coil unit is in attic together with a supplementary electric heat system. Can I use the existing coil with a new unit using new refrigerants instead of the old R22?

I just changed the motor on the Fan-coil unit after 20 years of operation and expect that the compressor will probably give up in the next year. I would prefer to do just the outside unit as the access to the attic is too small for new unit. (I assume that the existing unit was installed before the house roof was closed).

Would love to hear some expert opinions.
Nope replace both.

Or you'll have more trouble then you think you saved money on.
Charge won't be right for heating or cooling mode.

Replacing both will get you the efficiency your paying for. And keep the warranty intact.
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Old 01-21-2010, 08:19 PM   #7
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Originally Posted by czars View Post
I understand that most heat pumps don't provide much (if any) heat when the outside temperature is 40 degrees F or below and most or all of our heat comes from the heat strips in the air handler. Does any heat pump manufacturer actually turn the compressor off when the temperature gets low or do they just allow the compressor to run and consume power?
You have been badly informed.

A 3 ton 13 SEER heat pump at 17F outdoor temp, and 70F indoor temp can output 24,400BTUs of heat. While only using 3.1KWs. Giving it a COP of 2.3

Meaning that the electric resistance heat would have consumed 7.13 KWs to provide the same amount of heat.

Many heat pumps can efficiently provide heat at temps of 0 to -10F outdoor temps.

Some even at -30F.

So, for the most part. Leave the outdoor unit run. Until its COP is almost 1.
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Old 01-22-2010, 09:45 AM   #8
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If the COP is one it is simply recycling the heat that is picked up from the compressor motor and not picking up any heat from the evaporator. I think you can get kits that have a larger accumulator and heater to allow very cold temps.
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Old 01-22-2010, 02:45 PM   #9
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If the COP is one it is simply recycling the heat that is picked up from the compressor motor and not picking up any heat from the evaporator. I think you can get kits that have a larger accumulator and heater to allow very cold temps.
Won't help you any.

At a COP of 1.2 to 1.3, depending on area, and type of defrost board. It will cost you more to use the heat pump.

You have to allow for the defrost cycle penalty.
A 5 ton system in defrost can remove more then 1,000 BTUs of heat a minute.

A time and temp defrost board could be going into defrost every 30 minutes. For 3 minutes at 0.
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Old 01-22-2010, 05:38 PM   #10
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Won't help you any.

At a COP of 1.2 to 1.3, depending on area, and type of defrost board. It will cost you more to use the heat pump.

You have to allow for the defrost cycle penalty.
A 5 ton system in defrost can remove more then 1,000 BTUs of heat a minute.

A time and temp defrost board could be going into defrost every 30 minutes. For 3 minutes at 0.
Good point. However I really wonder if one really needs to defrost that much when its that cold. Heck you might get more heat from the ice that the air, they say frosted ice is a good insulator. LOL
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Old 01-22-2010, 05:50 PM   #11
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Usually at temps below 20 you don't need a defrost very often.
But time and temp systems don't know if there is frost on the coils or not. they just go into defrost.

On demand defrost systems won't do those wasted defrost cycles. They need to see X temp difference between coil and outdoor temp before they will defrost. So they give better performance at lower temps. As far as not wasting defrost cycles.

On demand still goes into defrost every 6 hours of accumulated compressor run time. To make sure the outdoor coil isn't oil logged.

Both ice and snow are great insulators.
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Old 01-22-2010, 08:16 PM   #12
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I notice lennox came out with low temp outside air switch. It shut off when its below 15 degs. I always tell people anything below 25 degs go turn t-stat to emerg.heat
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Old 01-22-2010, 08:22 PM   #13
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I notice lennox came out with low temp outside air switch. It shut off when its below 15 degs. I always tell people anything below 25 degs go turn t-stat to emerg.heat
Shutting off at 25 just increases their electric bills.

We get as cold as you. And if their heat pumps stops working at 20. They yell about how high their bill gets.
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Old 01-22-2010, 10:08 PM   #14
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Shutting off at 25 just increases their electric bills.

We get as cold as you. And if their heat pumps stops working at 20. They yell about how high their bill gets.
That's no joke. Went on three calls this week about high bills ($400+) and every one of them had electric back up with a HP lock out set at 25 degrees. Same sized and insulated houses with lock out set to zero were $125.
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Old 01-22-2010, 10:23 PM   #15
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That's no joke. Went on three calls this week about high bills ($400+) and every one of them had electric back up with a HP lock out set at 25 degrees. Same sized and insulated houses with lock out set to zero were $125.

I pity the people that hear they should lock out the heat pump at 20, 25, 30 what ever. And follow those instructions.

Have to explain why its wrong. And that their electric bill will be much cheaper with the lock out removed. or lowered to 0 or -10, or no lock out depending on the heat pump.

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