Remodeling - John R. Hall

John R. Hall

My next door neighbor is putting on an addition to the back of her home and I began to wonder about the process of adding more ductwork, a higher velocity fan, or even a higher-capacity split system. What do contractors advise to homeowners, or are they even involved in the process? I.e., would the builder subcontract additional hvac work or do it themselves? Would my neighbor be better off contacting a local hvac contractor to get an opinion or estimate?

GW

reply

Adding duct work to an existing system may be a problem. It certainly makes a difference how much sq ft is being added. Ducts are sized according to what CFM is needed at the time of the original installation. NOTE- you will find someone who will gladly extend on to the existing duct work, but the air flow will suffer, and you may not know this until after the guy has been paid!!

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Floyd

Boy, this can go many ways...
First, is it one or two stories????Heat and air??? I would assume it is a hot air system, and if so just increasing the fan capacity will do very little if the ductwork isn't sized properly. If the system was sized too big to start with maybe some new ductwork can be added to handle the extra load.
Gotta do a heat loss, figure out what the options are and go from there.
Builder may have a legit. sub that can do the work, but if I were the HO I would definitely want to have a strong say in the matter, too often the builder will bid the job out to the subs and take the low bid and price the job at the high bid and make a chunk of change..... then the HO really gets shafted!!!!
Have the HO get his own bids for that part of the work.
Have seen a lot of halfbaked "add ons" be careful!!!!

John Morrill

big addition? small addition?

I think we need much more information to make more valid suggestions. But yes, I would pay an HVAC contractor for his/her opinion. How many stories? How much more area compared to what is existing? What side(s) of the house, how good is the thermal envelope to be removed, and how well designed is the new space going to be? I agree with the posters above, that fan size and changing ductwork will change everything, but keep in mind that the cooling load does not necessarily have to increase in strict proportion to increasing floor space. Improvements in the thermal envelope can reduce the need for more cooling.