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Question DetailsAsked on 12/27/2013

is there a benefit to changing a 80% efficent propane gas furnace to a 90% efficent propane gas furnace

I am having to replace my heat pump and I am wondering if I should replace my propane gas furnace also. this would also allow me to upgrade the heat pump from a 13 seer to a 17 seer (duct work restricted to 17 seer)

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3 Answers

Voted Best Answer

Generally speaking, there is no inherent reason to replace a furnace when you replace your A/C, or vice versa.

For a quick shot at cost-benefit, look at your annual gas bill, deduct about $10-15/month for hot water heat, then multiply the remainder by 0.11 to get the approximate maximum possible energy savings you would get with a 90% versus 80% efficient unit. That assumes that ALL heat losses from ducts and from the room the furnace is in end up heating the house - not a likely scenario, as typically about 1/2-2/3 of your heating energy losses are due to lost heated air from ducts and into unheated areas like garages if you furnace is there. So, for example, if your bill is $1500/year for gas - what I pay for gas heat in a high gas cost area and with significant (what a lot of people would say ridiculously cold) winters, assuming 15% for hot water heating (which will not change) you would be spending about $1275 for heating gas. The more efficient furnace could save you no more than $140/year (11% of that), and if you figure in the typical losses that you will still be paying for, possibly only 1/2 to 1/3 of that. A new furnace is likely to cost at least $2000, more usually in $4000 range, so your payback period would be on the order of at least 15 and maybe more like 20-30 years if all your "losses" are in the flue gas, and 40-95 years if 2/3 of your heating losses are escaping heated air. So, if your current furnace is not over 20 or so years old and is working fine, from an economic standpoint a replacement makes little sense, and of course even a lot less if you do not intend to stay in the house indefinitely.

Answered 6 years ago by LCD


The SEER is is used for AC efficiency, 13 SEER is now the DOE minimum. For a heat pump efficiency COP or HSPF is used. The propane back up heating system is not related to the SEER or HSPF rating. Depending on your climate DD it may not be worth upgrading- 90% is condensing so you will also require PVC flue and condensing pump. Have your contractor show you the manual J calulations for your heat load.

Answered 6 years ago by hosey


Higher efficiency is always a benefit if the cost savings are substantial. How old is your existing equipment and what is the life cycle? What is the payback? Is the ROI positive for you? If cost is not important then the above questions are not either.

Poppy Ross

Source: Experience

Answered 6 years ago by PoppyRoss



In theory, any upgrade in efficiency is a good thing. The question becomes (best being answered by the heat load calculations), how long does it take to justify they expense.

In most homes, air sealing and insulation are a must and will help the lesser efficiency rated furnace perform better and actually save you more utility dollars in the long run as well as have a much shorter ROI period.


Answered 6 years ago by WoWHomeSolutions

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