Fresh air intake for hvac ????? | Ask Mason Knowles - SPF Consultant | Spray Foam Technical Questions and Answers | SprayFoam Magazine Q&A Forums

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daniel kempton Posted: Mar 07, 2008 10:08 PM	Fresh air intake for hvac ????? Newbie question I've been reading and reading on the spf industry and it seems like there are conflicting opinions. If you completely seal the house... exterior perimeter walls and the underneath of the roof sheathing, for a complete thermal seal. Does the a/c system need to incorporate a fresh air intake??
mason Posted: Mar 08, 2008 10:04 AM	When you use SPF to seal the whole house, (walls, basement and attic, it will reduce the air exchange rate per hour (ACH) in the house to around 0.2 ACH. Most houses HVAC systems (including fresh air intake and heat recovery units) are designed around 0.55 but can handle down to 0.35 ACH. The newer units are designed to recirculate 80% of the house air and bring in 20% new air. Just ask the HVAC guys to design around a 0.2 ACH instead of their standard 0.55 ACH and you will be fine. This means they will reduce the size of the air conditioner and the furnace but add air intake and exhausts to accomodate the reduced air exchange rate. This is usually a neutral cost issue. In older houses where you are only spraying the basement and/or attic, the foam will typically not go beyond 0.35 ACH and would not require additional ventilation unless there were issues of stale indoor air before the application.
Darren Gomez Posted: Mar 12, 2008 01:49 AM	You're in New Orleans right? Lots of foam guys down there not properly educating their customers. Always, always, always consult your HVAC contractor before installation of foam. The other problem in New Orleans is that there are a lots of fly by night A/C contractors. If this is Daniel K, who works for a waterproofing company give me a call you have my number. I'll lead you in the right direction Darren Gomez

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daniel kempton

Posted: Mar 07, 2008 10:08 PM

Fresh air intake for hvac ?????

Newbie question

I've been reading and reading on the spf industry and it seems like there are conflicting opinions. If you completely seal the house... exterior perimeter walls and the underneath of the roof sheathing, for a complete thermal seal. Does the a/c system need to incorporate a fresh air intake??

mason

Posted: Mar 08, 2008 10:04 AM

When you use SPF to seal the whole house, (walls, basement and attic, it will reduce the air exchange rate per hour (ACH) in the house to around 0.2 ACH. Most houses HVAC systems (including fresh air intake and heat recovery units) are designed around 0.55 but can handle down to 0.35 ACH. The newer units are designed to recirculate 80% of the house air and bring in 20% new air. Just ask the HVAC guys to design around a 0.2 ACH instead of their standard 0.55 ACH and you will be fine.

This means they will reduce the size of the air conditioner and the furnace but add air intake and exhausts to accomodate the reduced air exchange rate. This is usually a neutral cost issue.

In older houses where you are only spraying the basement and/or attic, the foam will typically not go beyond 0.35 ACH and would not require additional ventilation unless there were issues of stale indoor air before the application.

Darren Gomez

Posted: Mar 12, 2008 01:49 AM

You're in New Orleans right? Lots of foam guys down there not properly educating their customers. Always, always, always consult your HVAC contractor before installation of foam. The other problem in New Orleans is that there are a lots of fly by night A/C contractors. If this is Daniel K, who works for a waterproofing company give me a call you have my number. I'll lead you in the right direction

Darren Gomez

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