What is location?

Nat gas service is not available?

What is your cost for propane/gal and electric/KWH?

IMO

I live in southern Ohio. Propane was 2.29 the last time I filled up, and I don't have access to natural gas where I live.

Electric is about .15/kWh. We talked to one of the contractors about a heat pump to offset the propane use, but our ducts were undersized so it wouldn't work well in our house without turning this into a much bigger project.

Chris

Your comment about a heat pump would not work with your undersized duct work makes no sense. The required air flow for a propane furnace and a heat pump is going to be about the same.

If you can get an Infinity furnace for the about the price of a Comfort model then I would not hesitate getting the Infinity. You want a contractor who knows how to install it properly. The dual fuel set up with the heat pump would be a good way to save on operating costs.

>He particularly said that he advised against the 98% efficient furnaces due to their complexity.

This is the typical line used by contractors who have not bothered to keep up with training on the latest equipment, and don't want to get into a situation where it's clear they have no idea what they're doing. A lot of technology is more complicated than it used to be. Does that mean we should just stop innovation and advancement because they introduce more possible points of failure?

As for the Infinity 98, the modulating technology really isn't as new as it may seem. Rheem came out with their modulating furnace back in 1997 and since then, it has proved to be one of the most reliable on the market. The 2 stage technology in the Infinity 96 is even simpler and has been around even longer. It is true that if one of the parts unique to a modulating or 2 stage furnace fails out of warranty, it will be more expensive to replace than the corresponding part in a single stage furnace. Maybe it wouldn't be a bad idea to spring for a 10 year parts and labor warranty. But in the years that modulating and 2 stage furnaces have been around, there has been no evidence to suggest they are less reliable than their single stage counterparts.

Absolutely agree with Mike.

At the very least, a DF system is the way to go both with high eff 95+% eff furnace and a high eff heat pump.

Anything less is a big mistake.

Here s a fuel comparison to be used as a guide only.
Propane at 95% eff, HP at 2.75 COP. Results below.

Cost per 100,000 btu of useable heat
Heat pump: $1.60
Propane: $2.65

IMO

>Your comment about a heat pump would not work with your undersized duct work makes no sense. The required air flow for a propane furnace and a heat pump is going to be about the same.

It makes perfect sense. Even with today's higher efficiency furnaces that need more air moved than old ones, the properly sized furnace for a house will usually still require significantly less airflow than the properly sized heat pump for that house.

"...the properly sized furnace for a house will usually still require significantly less airflow than the properly sized heat pump for that house."

I could see that the furnace would be less, but significantly less?

Let's pick a hypothetical situation where you have a 80k BTU furnace, and a 3 ton heat pump. What air flows would expect to see for each in their high stages?

If the furnace were condensing, I would expect the airflow to be the same, about 1200 CFM. A few hundred CFM less if an 80%. However, in my experience 80K furnaces are more commonly matched with 4 ton outdoor units, which would need 400-600 more CFM than the furnace.

Having said that I do agree with both you and tigerdunes that the OP should look more carefully at a heat pump. I recommend getting answers to the following questions:

How big a furnace is needed?

How big an HP would be needed?

Max CFM the duct system can handle?

What would it take to get that to be enough for the properly sized HP?

This post was edited by hvtech42 on Sun, Nov 2, 14 at 17:35

That's a reasonable list.

It's never been asked if OP had air conditioning and if so the size of AC condenser.

Not necessarily true that 80 K condensing furnaces usually carry a 4 ton rated blower.

IMO

I thought an 80K furnace and 3 ton AC might be appropriate for the southern Ohio climate. This needs to be confirmed with with a load calculation.

The money saved on operating the heat pump would help pay for making ducts larger. I suggest getting additional quotes from contractors who are interested in installing a dual fuel system.

True, not all 80K furnaces have a 4 ton blower and of course, all this stuff varies by area. Personally, I see 80K/4 ton more than 80K/3 ton, so it is quite conceivable that airflow _could_ be an issue (may not be).