How to handle oversize quote

david_carySeptember 7, 2011

So I am building in a rural area where there really is a single major company. Their quote was fine and they have a good reputation except for one thing.

The house is 2100 sq feet split evenly on 2 floors and they want to do 2.5 ton down and 2 ton up in an area with a 91/26 design temp. My calcs put it at 2 and 1.5 with the best I could do on HVAC-calc. I am not particularly worried because the house has 80% east windows which really are overcounted in the manual J algorithm. They are counted the same as west windows despite the west being far more important as peak load.

The contractor response to me requesting the lower tonnage was "maybe we aren't the right contractor for you". It was handled by the builder so I don't have any more details of how it went.

Honestly, they put the ducts in the attic despite them being in conditioned space between floors and they left off a 12 foot overhang on some large windows. The infiltration was too high etc. My builder didn't want to point out their mistakes but just stated it was a customer's request.

My thought is to tell them we are putting awnings on all the windows and foaming the attic rafters or some other lie. But it might seem pretty transparent at this point.

I am definitely going to try to get other contractors but it really maybe going with someone 1/2 hour away that has a much higher quote and won't be as available if there are problems.

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veesubotee

Pay now or pay every year.

    Bookmark   September 8, 2011 at 7:59AM
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david_cary

Well the pay every year is a bit overstated. Under ideal conditions, this house is a $200 a year a/c bill. Oversized it might be $230. There was a study somewhere that quoted less than a 10% cost to the routine oversizing. To me the real issue is system life and humidity control.

    Bookmark   September 8, 2011 at 3:10PM
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weedmeister

Where is this again?

    Bookmark   September 8, 2011 at 5:37PM
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ionized_gw

30 minutes away in a rural area is not that much. I know a lot of people that have more than that to a food store or a fuel station.

    Bookmark   September 8, 2011 at 7:01PM
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david_cary

You are right that 30 min is not a ton but the price is also thousands more. The oversized quote has a rigid duct trunk where the others use flex. So there are a number of things that are more than the distance.

This is coastal NC.

    Bookmark   September 8, 2011 at 8:55PM
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weedmeister

For coastal carolina, I would think that 91/26 is a bit low. I don't feel that 0.5 tons would be that much oversized when it is 98f outside.

    Bookmark   September 9, 2011 at 1:18PM
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david_cary

I've found that 91 in a couple of areas. It was the HVAC-calc default and it was the contractor's manual J design temp. I agree though that it seems a little low. But even at 98 degrees, it didn't change the tonnage with my calcs. On a tight well insulated new house, the vast majority of heat gain is solar and internal which obviously is independent of outside temp.

There is a large mass outside the house that never gets above 80 and the wind always comes off of it so I think the 91 is actually right. While you might see temps of 98 2 miles inland, the waterfront temp is less. Feels hot when you are in the sun though....

    Bookmark   September 9, 2011 at 2:22PM
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energy_rater_la

guess they wouldn't consider zoning with actual zone dampers instead of multiple units??
the you could go with one unit and move in to dual stage/variable speed.

the pay not or pay every year isn't only cost to run
equipment but lessend humidity control, due to short cycling and parts wearing out faster because of so
many starts.

I'm in a rural area and we have lots of companies
that drive an hour to get to the job. but I guess it
depends on who you are comfortable with.
and I don't deal well with thinly veiled threats.

best of luck.

    Bookmark   September 9, 2011 at 8:21PM
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david_cary

Agree on the threat. I am trying to be practical though. We talked about the zoning option and the ductwork was a challenge. The other reason is trusting someone to get it right requires a whole level of diligence and this is a distance build.

    Bookmark   September 10, 2011 at 5:31AM
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energy_rater_la

I got you.
"The house is 2100 sq feet split evenly on 2 floors and they want to do 2.5 ton down and 2 ton up in an area with a 91/26 design temp. My calcs put it at 2 and 1.5 with the best I could do on HVAC-calc. I am not particularly worried because the house has 80% east windows which really are overcounted in the manual J algorithm. They are counted the same as west windows despite the west being far more important as peak load."

as I see it they are building in a fudge factor.
2.5 tons vs your 2 tons downstairs
and 2 tons vs your 1.5 ton upstairs.
they are sticking with that 400-500 sq ft per ton sizing.
this is a common problem with hvac contractors.
none of the smaller tonnage units will be vs/two stage
which is why I suggested on system.
in dealing with hvac contractors a lot I know the argument for the 2 ton upstairs instead of the 1.5 tons is that the equipment cost is the same. and it is really close, that is true.

one option would be to get an independent load calc
along with a duct design and sizing. this will cost you.
then you could shop for a contractor to install as per designed. of course you could run into the same problem
you are having with this contractor.
but the design of the ductwork and the sizing of the ducts would already be done. they would just install as designed.

if you do choose this company then make sure that all the ducts are mastic sealed..with hard duct the long seals and all the joints of the 90's connections to plenums and supply boxes along with plenum connections to equipment.
this would be a deal breaker for me. they would have to mastic before insulating the ducts. hard pipe leaks like a sieve.

then you could add a stand alone dehumidifier
to remove excess humidity. it will cost you a little bit to run, but the reduced humidity improves the comfort.
it is an affordable option.
the oversizing of a ton to a ton and a half...it could be
worse...(and it could be better) but if this is what it is..then the dehumidifier is one way to keep peace & comfort.

best of luck

    Bookmark   September 11, 2011 at 3:03PM
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SpringtimeHomes

I agree with you guys for the most part. The HVAC guys are also used to very inefficient envelopes. Are you sure that yours is that much better? 80% East windows sounds like a bad start...

    Bookmark   September 12, 2011 at 7:54PM
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david_cary

The ocean is towards the East. I could care less that it isn't the most efficient.

ERLA - Thanks for the reply. I will check on the mastic sealed but I am pretty sure that is code. Doesn't mean it isn't always done.

I am really just looking for a way to convince the contractor to change his mind. Things like telling him that all the windows will have awnings and agree not to hold him responsible if the house isn't cold enough.

    Bookmark   September 12, 2011 at 8:28PM
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