Builder's HVAC sub won't reduce a/c size

I'm having a builder build a 2300 sq.ft. ranch house, with all Low-E double-hung windows. My house has a full (unfinished) basement, and the main 1st floor has 8ft. flat ceilings. The attic has R38 blown-in insullation and R15 fiberglass high-desisty batts in the wall. The sheathing on the house is all plywood with a R2.5 insulated sheathing on top of that, and wrapped with tyvek housewrap. Exterior is all brick veneer.

The HVAC sub-contractor hasn't used Manual-J or Manual-D for the sizingm duct design nor heat load calc'. The furnace is a Bryant VS 2 stage "The Plus 80v"(315AAV) sized for Input: High 110,000 and 72,500 Low and Output: High 89,000 & Low 59,000.

They are going to use a SEER 10 Bryant 3.5 ton (561CJ042-F) A/C unit. I've been trying to get the builder to reduce the size of the A/C unit (house is in Chicago suburb area) given concerns on not having proper humidity in house while running the A/C, excessive Electrical usage (Com Ed rates), and probably fast cycle on/off times.

The HVAC sub won't budge - I even offered to sign a release for sizing to release him from a wrong sized unit (thus going against his recommendation). The builder requested the HVAC do this, but the HVAC sub won't compromise. I can't understand that if thei model home with 10 ft great room, west facing clear windows, a vaulted study and Master Bedroom can possibleby be sized the same for A/C (the furnace was an upgrade I requested.

I've even sized things with the HVAC-Calc software that I bought, but the sub is "set in his ways" to be polite - What else could it be? Any ideas on this sizing, and anything to get a properly sized unit installed by the builder.

Thanks in advance!

It's your money .....If the guy won't produce a heat load calc for your home then demand the contractor find someone that will.Or get your own contractor & send him packing.

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Originally posted by markwolf
It's your money .....If the guy won't produce a heat load calc for your home then demand the contractor find someone that will.Or get your own contractor & send him packing.

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Nice call Mark...

If I were the home buyer... It would be my way or the highway. Remind the builder that one of you is gone... the HVAC dude or the buyer.

Who do you think he will pick?

Do as mark says... or

Ask for a credit from the builder and apply that to the HVAC contractor of your choice!
(you pay the difference... you will be better off!)

Maybe the contractor knows that you would not be happy with anything less after a few years of operation. Maybe his experience tells him this. Maybe he is more concerned with yur comfort than yur electric bill.
Hoe much less did yu want to go with?

Ask the builder and the HVAC-sub,to sign that they will be responsible for the mold cauased by oversizing!

That might get their attention,not that they would sign .

This "oversize thing" is way over stated. Home owners are being encourged to install undersized equipment to get humidity control when there is low/no cooling load. It will only make a couple %RH difference during low load and no differnece with "no cooling load" conditions. Suggest installing the specified a/c. After verifying a humidity problem, get enough supplemental dehumidification to control the indoor humidity (<50%RH) with no cooling load. 100 pints per day of dehumidification handles a 2,500 sq.ft. of living space along with the basement and 50 cfm of fresh air ventilation. A well built, tight home should have some fresh air ventilation for oxygen replacement and make-up air for clothes drier, kitchen hood, and bath fans operation.
The problem is that the first a/c mfg. that admits their a/c is unable to control humidity during "low/no" a/c is the big marketing loser. A cool rainy week or two is the big test. After this happens several times for a couple years, basements have an odor and dust mites grow throughout the home. A wise a/c contractor hates the call about a/c running continuously or not being able to providing 75^F with 100^F outside. A slightly over-sized a/c with supplemental dehumidification allows t-stat set-up when unoccupied for 10 hours a day or away for days. Also cooling to 75^F during extremes, having visitors, and rapid cool downs, all while maintaining <50%RH.

Check with local/state codes and officials. He is probably required to do a load calc whether he likes it or not.

If 2300 square feet is the total conditioned space, that furnace will never high fire unless you have set back the temperature of that home and then are trying to bring it up to room temperature.

I stongly recommend using a contractor who can run a load and install properly sized equipment.

Make sure ventilation is addressed so that you do not have a winter time condensation and mold problem. A dehumidifier will not help you in the winter.



[Edited by Carnak on 07-25-2005 at 10:16 AM]

2300 sq ft home with 2300 sq ft basement is 4600 sq ft of conditioned space, the two stage 110,000 @ 80% AFUE does not sound too oversized, I would 'guess' 100,000 max input at 80%.

To me a ranch home was always a one story core floor or slab on grade. Did not catch the mention of a full unfinished basement below until later.

I've requested that they use a 3 ton unit. Either a
3 ton or even a 2 1/2 ton is more than the 1.5 ton unit per HVAC-CALC program calculation (total heat gain with the program calculated to 19,946 or 1.5ton, but that seems too small). The builder hasn't used anything less that a 2.5ton unit in the past on any of their models.

Appreciate everyones input!