Variable Speed Furnace - Cold Air Return

[dave16360]

So .... after weeks of research I finally decide to go with a Lennox Signature Series high efficency variable speed furnace and the best Lennox heat pumps available in my home which has zoned heating & cooling.

The problem is when they are installing the furnaces (yesterday) they tell me since my house only has a single cold air return duct that the variable speed furnaces won't work because they will compete with each other when both systems run. The local Lennox "engineer" confirms this is true.

My only other option now is to go with a two stage high efficency furnace, so I tell them to go ahead and remove the variable speed units today and they will replace with the two stage (at a reduction of $600 total for the pair).

What did I just loose by not getting the variable speed furnaces?

Is the $600 reduction fair?

The contractor finishes the installations tomorrow. I'm out of town on business and not feeling so good about this.

Frustrated in K.C.

[beenthere]

You have 2 units hooked to the same common return, hmmm.

Could they have just added another return.

Or are your units twinned?

[Christheheatingdude]

Originally posted by beenthere
You have 2 units hooked to the same common return, hmmm.

Could they have just added another return.

Or are your units twinned?



Makes sense if your furnaces are twinned together. Cannot twin Variable Speeds together.

However if they are not twinned, and are operating off of different stats, they could still end up working against each other regardless of wether they are Variable speed or single.

[trane]

Originally posted by Christheheatingdude

Originally posted by beenthere
You have 2 units hooked to the same common return, hmmm.

Could they have just added another return.

Or are your units twinned?



Makes sense if your furnaces are twinned together. Cannot twin Variable Speeds together.

However if they are not twinned, and are operating off of different stats, they could still end up working against each other regardless of wether they are Variable speed or single.

This is correct. The only way you can install two furnaces on a common return is if they have an actual twinning kit. Running them both on one thermostat or having a seperate thermostat for each one are only going to cause you problems. The twinning kit makes sure both blowers come on at the same time.