Three Fuel ?

[Jack2007]

Is it possible to have a heat pump with a heat strip plus furnace??

Here is what I'm thinking; If I could have a heat pump w/heat strip, so in defrost mode the strips would come on down to a temp of 32*, where the heat pump and strip is locked out so the furnace would take over.

Is this possible ??

It seems almost a waste to have a furnace kick on for just a few minutes during defrost. How much heat does a furnace even create during defrost?
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[beenthere]

Varies with the lenght of defrost cycle, and the BTU of the furnace.

Its possible if you have room for the strip heaters. And can find someone thats good with low voltage wiring.

[RDP]

I've done it

[Poodle Head Mikey]

No way I'm firing a 93% gas furnace for every defrost.

I going to try to not use any heat during defrost as I plan the chnage-over for a fairly mild ambient. But if that is uncomfortable - I have ten KW of electric heat ready to go.

[RDP]

No way I'm firing a 93% gas furnace for every defrost.

I going to try to not use any heat during defrost as I plan the chnage-over for a fairly mild ambient. But if that is uncomfortable - I have ten KW of electric heat ready to go.

Dude different folks different strokes.Besides down here you don't have that cold of a winter.For some reason that is what the customer wanted so that is what he got.I really didn't see the point but I get paid by the hr.

[beenthere]

No way I'm firing a 93% gas furnace for every defrost.

I going to try to not use any heat during defrost as I plan the chnage-over for a fairly mild ambient. But if that is uncomfortable - I have ten KW of electric heat ready to go.

What do ou considr a mild change over ambient..

[Poodle Head Mikey]

With a 90+ furnace cycling on - it's probably the better part of five minutes before it is producing any noticable amount of heat. And by then the defrost is likely over anyway.

The electric heat elements are almost instant-on.

For 'mild ambient change-over' I have in mind maybe thirty or thirty-five degrees. But like so many things in my Life there will, no doubt; be some tweaking involved.

Of course; I do live ever in the hope that beenthere will come to my design-rescue, tell me what to do for the best, and so spare me the tedious agony of overcoming my own fumbling attempts at empirical sorting. <g>

[beenthere]

Don't know if I ever seen a 90&#37; furnace take 5 minutes to put out heat.
2 to 3 minutes though.

Best set up. A unit with On demand defrost. Cuts down on those needless defrost cycles.

You must have a tall basement to get a heat kit in your plenum and be far enough above your coil.

[Poodle Head Mikey]

And let's say that the defrost time on the HP will be maybe five to ten? So do we really want the furnace starting and then stopping in five or ten minutes? I don't.

Aren't all heat pumps using 'on-demand' defrost now?

My cellar isn't all that tall - but it is sixty feet long.

PHM
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Don't know if I ever seen a 90% furnace take 5 minutes to put out heat.
2 to 3 minutes though.

Best set up. A unit with On demand defrost. Cuts down on those needless defrost cycles.

You must have a tall basement to get a heat kit in your plenum and be far enough above your coil.

[beenthere]

Lot of HPs still use time and temp defrost conttrols.

6 one way, half a dozen the other.

May not get to full efficincy in 5 minutes. But the furnace putting heat into the evap coil, also shortens teh defrost time, by heating up teh OD coil quicker.

Electric strip after the coil, 100&#37; efficiency right aways, but adds no heat to the ID coil, so the OD coil takes longer to defrost.

Which method is better, will depend on your rates, winter OD ambient conditions.

[Poodle Head Mikey]

Wouldn't that give me the best of both concepts?

PHM
---------

Lot of HPs still use time and temp defrost conttrols.

6 one way, half a dozen the other.

May not get to full efficincy in 5 minutes. But the furnace putting heat into the evap coil, also shortens teh defrost time, by heating up teh OD coil quicker.

Electric strip after the coil, 100% efficiency right aways, but adds no heat to the ID coil, so the OD coil takes longer to defrost.

Which method is better, will depend on your rates, winter OD ambient conditions.

[beenthere]

Yes it would.

How practical it is to do it. I guess would be dependant on the install set up.

But should for all practical purposes give you shorter defrost cycles, and tempered air temps during those defrost cycles.

Let us know how it works in the real world. Cause it does look good on paper.

[Airmechanical]

Wouldn't that give me the best of both concepts?

PHM
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all that dust burning off the heaters at the beggining of the season getting impacted in the evaporator



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