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HVAC in New Construction

Posted by drauseo (My Page) on
Mon, Sep 24, 12 at 13:56

I am currently building a single family home in MD and our builder (Beazer Homes) has just switched their building practices in MD to adhere to the 2012 Energy Codes.

Some of the 2012 Energy Code changes include:

1" dow board insulation before the Tyvek goes on

R15 insulation on 2x4 framed walls

R19 insulation on 2x6 framed walls

R38 insulation in the attic

low e windows

additional wrapping of all ducts

higher standards for blower door testing

no recessed lighting on the top floor

whole house mechanical ventilation system (I think)

My 2 questions are:

B/c my house will have the additional 1" dow board insulation along with the other energy code changes, is it possible for a house to be sealed too tightly?

As part of the redesign and to conform to the new codes, my builder is no longer offering dual zone HVAC systems. In the past there was always a system for the top floor and system for the basement and main level. My house has 3,000 sq ft between the main level and top floor and a finished basement of probably an additional 1,000 sqft. Here are the specifics of my HVAC system: Manufacturer is Goodman and the AC model # is GSX13 (4 tons) and the furnace is GKS9 (90,000 MBTU/h). This system is single zone.

I know very little about HVAC systems but this seems like it will not be able to properly regulate the temp throughout the house. Based on the info above what is your opinion? Is there anything I should ask the builder to change (although they probably would not)?


Follow-Up Postings:

RE: HVAC in New Construction

it takes more than adding blue board on the exterior
of walls to make a house tight enough to require
make up air.
however, getting a house tight enough to require
make up air isn't a bad thing.
in my world..we call that build it tight, ventilate
it right.

if the house tests (with a blower door) below
a certain amount of air changes per hour, then
ashre 60.2 ventilation strategy is used to determine
how much fresh air is needed.

zoned systems are not achieved with multiple systems.
zoning is one hvac system with multiple t-stats
that control motorized dampers at the plenum of
the unit. you should still be able to do that, if
the hvac company has installed zoned systems in the

if the ducts are designed well, there should be
no problem with multiple stories. duct design &
sizing of ducts should be done prior to install.

I don't get the bit about additional wrapping of ducts.
R-value should be R-8 all ducts, plenums, and supply
boxes should be mastic sealed.
also all recessed lights should be ICAT. insulation
contact air tight. then it doesn't matter if
they are in between floors or in attic.

one of the benefits of building better..and foam sheathing
to exterior is a definate better that
hvac systems are downsized.
do you have a load calculation for your new build?

also is the goodman 13 SEER?
if so you may want to invest in more than just
the lowest efficiency manufactured.

I'm sure they will change whatever you are willing
to pay the upcharge for.

best of luck.

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