# Heat Pump w/Propane backup Condensing Furnace



## macattack_ga (Jan 11, 2019)

Is there such a thing as Heat Pump w/Condensing Propane Furnace for backup (below 40f)?

We really should replace our older Oil Furnace (ducted air) and older A/C.
Rambler/ranch w/ finished basement in Northern Virginia.
We heat mostly w/ our wood stove and don't use the basement much.It's too cold down there 

No natural gas (NG), but it's an option ($). Neighbor across the street has NG.
We have a detached garage with a propane furnace. So we have a tank and the conduit in place to get propane to the house (or NG to the garage). I'd like to get a gas stove (cooking) at some time.

I'd like to repurpose the chimney the oil furnace is using for a free standing wood stove. So would have for duct work moving the HVAC equipment.

Would a dual fuel heat pump w/ direct vent work for  us or should we consider something else? Or read?
Am I using the right language describing the system?

Thanks!


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## KeithO (Jan 11, 2019)

An electrician could probably do what you are looking for by using 2 thermostats, some relays  to lock out the different systems when above or below the threshold.   Maybe there is a smart thermostat out there which can deal with 2 different heat sources. Im guessing when you say 40F you mean outside air temperature ?


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## macattack_ga (Jan 11, 2019)

KeithO said:


> An electrician could probably do what you are looking for by using 2 thermostats, some relays  to lock out the different systems when above or below the threshold.   Maybe there is a smart thermostat out there which can deal with 2 different heat sources. Im guessing when you say 40F you mean outside air temperature ?



Yes. 40F outside air.

There are dual fuel systems (heat pump & gas) in the market now. 
I was curious if they were worth the expense & 
if a direct vent version (venting using PVC) existed.

I should probably find an HVAC forum... but the folks on Hearth.com are pretty sharp.

Thanks!


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## KeithO (Jan 11, 2019)

See the manual for this Honeywell thermostat


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## DBCOOPER (Feb 2, 2019)

Yes, the air handler part of the system doesn't care what you use for backup heat. It just has a coil and the connections for the controls so it would be the same as a gas fired furnace with air conditioning. The problem with direct vent high efficiency furnaces is that they consume a lot of electricity to extract all the heat with fans.


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## k0wtz (Feb 10, 2019)

macattack_ga said:


> Yes. 40F outside air.
> 
> There are dual fuel systems (heat pump & gas) in the market now.
> I was curious if they were worth the expense &
> ...


We have heat pump has backup Goodman


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## k0wtz (Feb 10, 2019)

k0wtz said:


> We have heat pump has backup Goodman


Any gas furnace guy can fix you up get 3bids though..  Our furnace high e vents through wall!


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## macattack_ga (Feb 10, 2019)

k0wtz said:


> Any gas furnace guy can fix you up get 3bids though..  Our furnace high e vents through wall!



Cool. Sounds like it's a pretty common setup.  Thanks!


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## wooduser (Feb 10, 2019)

macattack_ga said:


> Would a dual fuel heat pump w/ direct vent work for us or should we consider something else? Or read?




To be pedantic:

High efficiency gas furnaces are typically condensing furnaces.  That means that the combustion gasses are cooled down to about 120 degrees or so,  which causes the considerable amount of water vapor created by burning the hydrogen in gas to condense into water.  Just as it takes a lot of energy to boil water into steam,  if you condense steam from that combustion into water,  you get a lot of energy back,  plus additional efficiency by cooling the combustion gasses and water down to 120 degrees.

\By contrast,  direct vent equipment is a two tube system that takes combustion air from outdoors to burn the gas,  and then vents the combustion gasses outdoors through a second tube.  No condensine of combustion gasses.


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## wooduser (Feb 10, 2019)

macattack_ga said:


> No natural gas (NG), but it's an option ($). Neighbor across the street has NG.




Ummm.  If your neighbor has natural gas,  it really shouldn't cost much,  if anything to get a typical gas service run to your home.  Have you checked with the utility to find out about that?

The gas utility I used to work for would go for that kind of new service like a duck on a junebug,  at no cost to the new customer.


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## wooduser (Feb 10, 2019)

macattack_ga said:


> No natural gas (NG), but it's an option ($). Neighbor across the street has NG.
> We have a detached garage with a propane furnace. So we have a tank and the conduit in place to get propane to the house (or NG to the garage). I'd like to get a gas stove (cooking) at some time.




If you use little oil,  there may be little reason to buy a new furnace of any kind. 

If the lack of heat causes you not to use the basement,  that's a pretty big disadvantage to heating with wood.

<<We have a detached garage with a propane furnace. 


So you have a wood stove as a primary heat source,  an oil furnace for secondary heat of the house and a propane furnace or heater to heat the garage?  That's quite a mish mash of equipment.  

What is the purpose of heating the garage,  and how much heat does it get?

My bias is usually to do nothing unless there are compelling reasons to make changes,  and I don't see any from what you have listed,.

Natural gas is usually a cheaper fuel than either oil or propane. Longer term I might look at removing the propane and oil furnace  and using natural gas to heat the basement and garage as needed and as backup heat for the main part of the house.


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## macattack_ga (Feb 11, 2019)

wooduser said:


> To be pedantic:
> 
> High efficiency gas furnaces are typically condensing furnaces.  That means that the combustion gasses are cooled down to about 120 degrees or so,  which causes the considerable amount of water vapor created by burning the hydrogen in gas to condense into water.  Just as it takes a lot of energy to boil water into steam,  if you condense steam from that combustion into water,  you get a lot of energy back,  plus additional efficiency by cooling the combustion gasses and water down to 120 degrees.
> 
> \By contrast,  direct vent equipment is a two tube system that takes combustion air from outdoors to burn the gas,  and then vents the combustion gasses outdoors through a second tube.  No condensine of combustion gasses.



Condensing and direct vent equipment are two different things. Your description make sense. (and I didn't know).

pedantic is one of my favorite words. 




wooduser said:


> Ummm.  If your neighbor has natural gas,  it really shouldn't cost much,  if anything to get a typical gas service run to your home.  Have you checked with the utility to find out about that?
> 
> The gas utility I used to work for would go for that kind of new service like a duck on a junebug,  at no cost to the new customer.



That's what I thought too! I looked into it a couple of years ago and they made it seem like a big deal. I'll check again.



wooduser said:


> If you use little oil,  there may be little reason to buy a new furnace of any kind.



YES! Wholeheartedly agree! Better is often the enemy of good enough!



wooduser said:


> If the lack of heat causes you not to use the basement,  that's a pretty big disadvantage to heating with wood.



Exactly.




wooduser said:


> <<We have a detached garage with a propane furnace.
> 
> 
> So you have a wood stove as a primary heat source,  an oil furnace for secondary heat of the house and a propane furnace or heater to heat the garage?  That's quite a mish mash of equipment.
> ...



Previous owner built the garage with the idea of switching from LPG to NG (just a jet change I think).
I only use it on the weekends, and I'm too cheap to run it all week. So not much... at the moment,



wooduser said:


> My bias is usually to do nothing unless there are compelling reasons to make changes,  and I don't see any from what you have listed,.



You get it!



wooduser said:


> Natural gas is usually a cheaper fuel than either oil or propane. Longer term I might look at removing the propane and oil furnace  and using natural gas to heat the basement and garage as needed and as backup heat for the main part of the house.



Exactly. Switching to a heat pump w/ LPG backup and then at some point switching that equipment from LPG to NG was what I was thinking. (I am assuming most equipment can be changed from LPG to NG).


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## wooduser (Feb 11, 2019)

macattack_ga said:


> Exactly. Switching to a heat pump w/ LPG backup and then at some point switching that equipment from LPG to NG was what I was thinking. (I am assuming most equipment can be changed from LPG to NG).




You could do that,  but I'd look carefully into going direct to natural gas if you use or plan to use much fuel other than wood.  Natural gas is bound to be cheaper, and I'd be surprised if it cost much,  if anything,  to get natural gas service since your neighbor already has gas.


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## wooduser (Feb 11, 2019)

You might consider trying to operate just the fan on your current heating system,  which would likely distribute heat around the house,  heating spaces more evenly,  particularly the basement.  That would be especially true if the return air for the furnace is taken from the area heated with wood.

Of course,  that will tend to cool off the area currently heated with wood,  since much of that heat would be distributed around the house,  heating the basement,  duct work,  crawl spaces and such.  

But it might be worth a try to see if it's useful;.

How well do the bedrooms get heated with your current practices?


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## macattack_ga (Feb 15, 2019)

wooduser said:


> You might consider trying to operate just the fan on your current heating system,  which would likely distribute heat around the house,  heating spaces more evenly,  particularly the basement.  That would be especially true if the return air for the furnace is taken from the area heated with wood.
> 
> Of course,  that will tend to cool off the area currently heated with wood,  since much of that heat would be distributed around the house,  heating the basement,  duct work,  crawl spaces and such.
> 
> But it might be worth a try to see if it's useful;.



That is a good idea. I've gone a step farther by switching off the A/C compressor and setting the thermostat to cool (fan only) when the upstairs gets warm and cut off when the upstairs cools too much. I think (know) it works ok, but the wife... 



wooduser said:


> How well do the bedrooms get heated with your current practices?



On a mild day, 35F outsite, the bedrooms might be 70F and the basement 50F (living room w/ stove a 75+F). 

I'm kinda leaning towards leaving good enough alone. It's a decent older/smaller house, but in a neighborhood where they are tearing down decent houses and building (what I call) McMansions... so major improvements might be a waste as far as resale.

Thanks for kicking around some ideas.


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## wooduser (Feb 15, 2019)

macattack_ga said:


> Thanks for kicking around some ideas.




Always the cheapest kind of home improvements!


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