HVAC Sizing Problem

tblaney

We recently built a house that was completed in March. From day one I had been questioning the heating contractor about the size of the furnace. After we only a few weeks of being in the house with Wisconsin winters, I noticed problems maintaining temp. This summer the contractor completed the job by installing an AC unit. We found even with a cold summer, the AC was not handling the load.

I had been in contact with the contractor who keeps claiming it was sized correctly. The house is energy star rated so at min some calculations were done, but I am not sure they were followed.

I ended up buying a HVAC load program to run numbers my self. What I am finding out is the funance just makes the load requirements, 79,000 with no room to spare. The ac is undersized, at 3 tons. The program calls for a 4.5 ton unit. The problem I believe the contractor ran into is the furnace is only capable of handing a 3 ton AC unit.

My questions are now, what should I expect from the contractor? Who should help with this problem the builder, energy star, or the contractor? Why should I now have to fork out more money to fix a problem that the contractor should have known up front? I would not expect that average person to have to calculate heating and cooling loads to see if of units are sized correctly?

HVAC Doc

You need to get together with all 3 (Builder, COntractor, and Energy Star folks) and present what you have found. It is hard to say "Yes you are 100% correct" or the "Contractor is right, you didn't figure it all correctly" over the internet sight unseen. Present your load calculations and how you figured them. Have all your facts such as insualtion values, windows, doors, roof, etc. everything you plugged into that load calculation program. Compare between yours and the contractors Manual J he submitted. In most areas, to even get Energy Star rebates a proper load calc. has to be submitted. Find out where the discrepancies are. Something may have changed that he did not take into account for during the building process. Likewise, you could be thinking something is less insulated than it really is. Be prepared to do walk throughs on your home to verify between all parties involved. Another area that may need to be looked at is the duct work and the layout of returns/supply vents. An improper duct system can make even the most perfectly sized system perform poorly. A manual D residential duct design will help in that area. Good luck and realize it may have been an honest mistake somewhere down the line either with a change from the builder or contractor that neither made the other aware of or was honestly forgotten, not mentioned, or didn't think it would be "that big of deal". Likewise, I also can understand not wanting to pay for either or boths goof ups. Let us know how it turns out.

tblaney

Just wanted to post an update. I talked seperatly with the builder, energy star, my lawyer, and the contractor. All very willing to help out. I talked with the heating contractor last and he came out to look at the system himself. He noticed right away before we got to the heating calcs that the air flow was really low. He suggested changing the furance to the next larger size which will increase cfm. He is also putting in a new lead in the great room.

The contractor was extremely helpful in the situation!

Thanks for all the help and access to the information that made me a more aware consumer!!!