short cycling brand new Rheem furnace

twin8885

I posted this on another forum and it just seemed to be a big joke, so I thought I might get better advice here.

I bought a 3000 square foot home that had a furnace that needed to be replaced. The previous one was 120k BTU and I had 4 estimates for a new system and 3 of the 4 people recommended it be replaced with a 125k system.

I ended up going with the one guy that recommended a 100k rheem system, but I asked if we could do a 125k since the others recommended it.

The system is now installed and seems to be short cycling. I live in a split level, so it has 4 small floors and the 3rd floor gets much colder then the rest of the house. I assume the system is marginally too big for the house.

The guy that installed the system said that the 3rd floor has an undersized duct (8x8) so he recommends putting in a larger duct to accommodate air flow and that he can turn up the fan which will stop the short cycling.

I just shelled out 1000's of dollars for this new system, so the advice on the other forum to throw this one away and get a smaller system isn't really appreciated.

Would anyone have any other advice other then replace it?

pecmsg

So the contractor recommended 100K but you insisted 125!
the old 120 input was what output 100?
the new higher efficiency unit is trying to squeeze maybe 15 or 20% more BTU’s. 

Add to that duct issues. 

twin8885

It's a 125k 80 percent efficiency is what I have and that was the same as the old system. He had originally quoted it for 100k, but I mentioned all the other proposals I had were for 125k and he said we could go up to that if I wanted, so I said sure.

EBEBRATT-Ed

@twin8885

The only right way to size a furnace is to do a heat loss of the house.

It seems that was not done so your flying blind.

When you talk furnace size in BTUs you need to state weather that is input or output

I am guessing your talking input

It's likely that the 100,000 input furnace would be too large.

Up sizing is now causing you short cycling

You putting more heat into the furnace than the ductwork and the fan can distribute.

Download the Slant Finn ap and do the heat loss that should have been done

Then we will know the options

Jamie Hall

And there are options. It just may get slightly interesting... not to worry. We'll figure something out.