Carrier Infinity vs Comfort furnace

[jeffvdgo]

Hello,
I'm replacing our 20 year old 80% furnace with a new 95% furnace (furnace only - no AC) taking advantage of some state and utility rebates going on now here in CO. I have 2 bids from contractors recommending different furnaces, and would like advice on the pros and cons.

One contractor is recommending a Carrier 58HDX100-20 (single stage Comfort series). The project includes replacing most of the current flex duct with sheet metal ducting and keeping flex for the short runs to the registers. One major exception is a long flex run from the basement up a chase into the attic and over to 2 bedrooms. The house was built in 1884, and there is no other way to get a duct to those rooms without major remodeling. This contractor is recommending the single-stage furnace because he says the variable-speed Infinity series would be slow to heat the house due to the high static pressure caused by this run. The high static pressure would cause the Infinity to lower airflow and heat output.

The other contractor is recommending an Infinity ICS and says he doesn't think slower heating due to high static pressure will be a problem.

I suppose a third option (my idea, not suggested by the contractors) is to find an alternative way to heat those long-run bedrooms and get rid of the long flex run entirely.

I've searched these forums and have found some reports of slow heating with the Infinity series, but also a lot people very happy with them. Any advice?

thank you!

[seatonheating]

Variable speed blowers operating under higher static will achieve required airflow, but at a cost. These costs are, higher wattage/electricity usage, noise, and shorter motor lifespan.


A good contractor should be able to solve this issue if most of the duct is accessible.

Manual D for starters.

[jeffvdgo]

Thanks - I should add that replacing the long flex duct isn't an option. It's not accessible without tearing out walls and floors which would more than double the cost of the project. So it's either work with the flex or find an alternative so it can be abandoned.

[seatonheating]

Thanks - I should add that replacing the long flex duct isn't an option. It's not accessible without tearing out walls and floors which would more than double the cost of the project. So it's either work with the flex or find an alternative so it can be abandoned.


Chances are the run isn't the problem, it's the balancing of the entire duct system.

Find someone who can perform a Manual J on the structure. This will tell them how much airflow each room needs. They can then in turn, apply this to Manual D. This will involve changing the configuration and sizing of the duct system with proper balancing dampers. If they scoff at this notion, find someone else.

Get this fixed before you even start talking about equipment.

When I go into someone's house, more often than not, we don't even discuss brand or equipment. I assess the duct system first.

Good luck.

[sjones]

If you wanted to abandon the run for the 2 rooms you could look at a ductless mini split unit. You would just have to run some copper lines from the room to the outside unit and a drain line.

[skippedover]

:ditto: Also, if you're not going to cool with it you don't even need the drain. There's no condensation in the heating mode. You should do a Seaton said and get the Man 'J' plus have the static pressures measured. I would advise against a variable speed blower in a high static situation. Your money would be better spent to resolve the high static first. You could either abandon the long run completely or let it do what it can for the room and let the ductless take over from there. Good solution!!

[tedkidd]

Infinity if you plan to stay, Comfort if you are going to dump the place. (Multiple stages and variable speed drive will make the place much better balanced and save significant energy over the long run.)

Also if you plan to stay get an energy audit. It may need to include duct diagnostics and room by room heat load so you know how out of balance the duct work is. Often the audit will determine you can improve comfort and balance by sealing leaks in your basement and attic and leaving your duct work alone, although switching the easy stuff to tin is probably a good idea.