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I'm a builder planning my first conditioned attic and have questions and concerns.

1. We build slab on grade. Any problems placing sealed combustion furnaces (Carrier) and water heaters (Navien) in the conditioned space? My concern is that I assume they are at least somewhat leaky (CO, CO2, etc.). If so, does that pose a problem to IAQ?

2. I'm planning on using a balanced mechanical ventilation system (another first for me). I have read much on this website and others about ERV's, HRV's and other options, but am still having difficulty in choosing one. Bringing fresh air directly into the central air returns via a controlled damper sounds appealing and more economical. I build only spec homes so cost is definitely a deciding factor for me. The home will be in Oklahoma City which is kind of in the middle of hot & humid and cold. We get both extremes, but not for long periods of time.

Any suggestions are appreciated
Thanks.

Asked by James Fincher
Posted Tue, 02/23/2010 - 18:49

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4 Answers

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Sealed combustion appliances are required in some building efficiency programs (just as they've been required for a long time in manufactured housing) because they eliminate the problem of backdrafting of combustion products due to stack effect and mechanical ventilation pressures.

Of course the effectiveness of the sealed combustion is largely a factor of the quality of installation. Keep exhaust runs as short as possible, seal all joints, and protect the outlet hood from snow. Every tight house requires controlled mechanical ventilation for IAQ and should also have CO detectors (it's the law here in VT).

If you have any appreciable air conditioning season with high outdoor humidity, then an ERV would be the most cost-efficient option since it lowers the energy cost of dehumidifying indoor air. The most efficient balanced ventilation systems are stand-alone. You can piggy-back the supply side of the ERV into the return plenum of the HVAC (beware of doing this with heat pumps since they can pick up condensate and recycle it back into the house), but it may be more difficult to balance the system.

Simply using a controlled intake damper does not move fresh air when the air handler fan is not running during the swing seasons (unless you add a fan timer). But air handler fans are more costly to run than HRV/ERV fans. So, as with most mechanicals, cheaper up front means more costly for the homeowner.

Answered by Riversong
Posted Tue, 02/23/2010 - 19:37

2.
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If you use a mini-split HVAC is the ERV still a good idea to have?

Answered by A.K. Harrison
Posted Sat, 03/26/2011 - 18:00

3.
Helpful? 0

A.K.,
A ductless minisplit unit provides heating or cooling. It has nothing to do with mechanical ventilation.

Any tight home needs a mechanical ventilation system. Such systems are usually separate from a home's heating and cooling system. To learn more, see Designing a Good Ventilation System.

Answered by Martin Holladay, GBA Advisor
Posted Sat, 03/26/2011 - 20:14

4.
Helpful? 0

James,
One option you have in OKC is to call Kelly Parker @ Guaranteed Watt Saver or www.gwssi.com for a complete hvac system design. I've worked with them in the past and they are good. If this is your first try, please do it right from the start. You realy need an independent hvac designer and tester after is all done.

Answered by Armando Cobo
Posted Sat, 03/26/2011 - 22:18

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