Air Exchanger needed??? | Ask Mason Knowles - SPF Consultant | Spray Foam Technical Questions and Answers | SprayFoam Magazine Q&A Forums

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Author	Comments
Corey Degetaire Posted: Oct 23, 2008 12:03 PM	Air Exchanger needed??? Having 3.5" OC in the exterior walls, and 6" OC in the attic above the ceiling of the conditioned area. Will this combination require the need for an air exchanger?
Eric Smith Posted: Oct 23, 2008 06:02 PM	Ultimately depends on how tight the rest of the home is going to be (i.e. windows, doors, exhaust fans, etc). I would say that you are real close to the 70% BAS mark.
mason Posted: Oct 25, 2008 08:38 AM	A blower door test would confirm the need for an air exhanger. On a typical house with 4 persons, DOE and EPA recommend that air exchanges average around .35 ach (air exchanges per hour). Most houses that are built without sprayfoam average over .55 ach and some around 1.5 to 2.5 (older construction) When doing a retrofit, the sprayfoam typically tightens up the house to around the .35 ach recommended by DOE, so an air exchange may not be needed. A good rule of thumb is in most retrofit situations where only the attic and/or basement/crawlspace is sprayed an air exchanger is not typically required, In new construction, where the walls, basement, crawlspaces and attic/cathedral ceilings are sprayed, the house typically averages .20 or lower ach. So in those cases an air exchanger would most likely be required. (windows and doors make a difference, so check the U value of them to determine their relative air sealing efficiency.) It is a good idea for a contractor to partner with a good HVAC company and perform blower door tests on a number of houses that represent the dominant type of construction in your area. Then you can get a good idea of the relative tightness of the homes in your area, (both before and after application of foam).

Author

Comments

Corey Degetaire

Posted: Oct 23, 2008 12:03 PM

Air Exchanger needed???

Having 3.5" OC in the exterior walls, and 6" OC in the attic above the ceiling of the conditioned area. Will this combination require the need for an air exchanger?

Eric Smith

Posted: Oct 23, 2008 06:02 PM

Ultimately depends on how tight the rest of the home is going to be (i.e. windows, doors, exhaust fans, etc).

I would say that you are real close to the 70% BAS mark.

mason

Posted: Oct 25, 2008 08:38 AM

A blower door test would confirm the need for an air exhanger. On a typical house with 4 persons, DOE and EPA recommend that air exchanges average around .35 ach (air exchanges per hour).

Most houses that are built without sprayfoam average over .55 ach and some around 1.5 to 2.5 (older construction)

When doing a retrofit, the sprayfoam typically tightens up the house to around the .35 ach recommended by DOE, so an air exchange may not be needed.

A good rule of thumb is in most retrofit situations where only the attic and/or basement/crawlspace is sprayed an air exchanger is not typically required,

In new construction, where the walls, basement, crawlspaces and attic/cathedral ceilings are sprayed, the house typically averages .20 or lower ach.

So in those cases an air exchanger would most likely be required. (windows and doors make a difference, so check the U value of them to determine their relative air sealing efficiency.)

It is a good idea for a contractor to partner with a good HVAC company and perform blower door tests on a number of houses that represent the dominant type of construction in your area. Then you can get a good idea of the relative tightness of the homes in your area, (both before and after application of foam).

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