Unvented attic and heat pumps | Ask Mason Knowles - SPF Consultant | Spray Foam Technical Questions and Answers | SprayFoam Magazine Q&A Forums

Q&A Forums

Author	Comments
Alex Ek Posted: Jul 19, 2010 02:24 AM	Unvented attic and heat pumps First time posting so I must say hello to all. I have scoured the forums and articles on Masons site to find my answer along with contacting BASF tech to forward me documents that might help with this question. I have a customer who is an HVAC installer who is sure that if we spray ccSPF to the underside of his roof to create an unvented attic that we are demanding to much from his heat pump to condition that extra space. I've shown him what articles I have found that talk about being able to downsize a system once ccSPF is installed. I used the "thermos bottle" analogy to no avail. He thinks it is a great idea for cathedral ceilings, but not attics. Is there any real data,tests,documents etc that will allow me to speak more confidently on this? Thing is, I believe if we helped him understand how this works to his benefit he would start promoting this application to his customers. We spray BASF spraytite 178 in the Pacific Northwest.
Posted: Jul 21, 2010 06:16 AM	he may be right... there is a good article about this in sprayfoam mag from spfa.org...i think it was the most recent issue...(not a member,,join,,be,,all that you can be,,,tell em 'dude sent ya),,, a brief synopsis...in some of these attics you are adding more cubic feet of "passive conditioned space" to the load than the "active conditioned space" below...but load is load none-the-less,,(physics is fizzics),,and a savey hvac contractor,,,one who does load calculations to size his equip,,,will recognize this additional load and size accordingly...you may want to seal at the level of the drywall ceiling in some of these applications... hope this hillbilly explanation helps.. dude :)
mason Posted: Jul 21, 2010 08:47 AM	There are some very good articles on unvented attics at Building Professional Consortiums website. Or just email me and I will forward them to you. masonknowles@aol.com
Alex Ek Posted: Jul 21, 2010 04:36 PM	Thank you Dude and Mason. I met with another HVAC contractor today and had him run his heat load calculations ( some piece of software he has )on a typically 4/12 pitch roof 1400 sq ft attic space which is common around here and according to his numbers a two ton system ought to be sufficient where without the foam a three ton system would be required. I know this won't work for every application but it is helping build a case for this issue. Do you guys feel it would be a benefit to do a calculation like this on each attic system to determine if we should spray the roof deck or the drywall ceiling? Mason I know your ceiling was sprayed and you seem to like it, was that at your request or did it make more sense to do it that way vs. the roof deck for other reasons? I will email you for those articles.
mason Posted: Jul 22, 2010 10:54 AM	At the time I insulated my attic, I had no choice. In 2003, building codes in my area did not allow unvented attics so I was forced to spray the foam on the floor of the attic. I would have preferred to spray the underside of the roof deck since I had tons of ducts in the attic. So, I added another layer of insulation on the ducts, it seemed to help. At the time, I couldn't spray the ducts with foam, which you can do now. I sold the house last year, so I guess it will stay the way it is. My wife incidentally was complaining last year that our energy bills had not gone done from before we had the attic insulated with foam. I reminded her that they had not gone up since 2003 even though energy costs have gone through the roof since then. Now we bought a house in Savannah that has only fiberglass insulation. And last months electric bill was $380 for a 3000 sq ft house. Guess I am going to have to spray some foam in it next year. Have to save up my pennies first.

Author

Comments

Alex Ek

Posted: Jul 19, 2010 02:24 AM

Unvented attic and heat pumps

First time posting so I must say hello to all. I have scoured the forums and articles on Masons site to find my answer along with contacting BASF tech to forward me documents that might help with this question. I have a customer who is an HVAC installer who is sure that if we spray ccSPF to the underside of his roof to create an unvented attic that we are demanding to much from his heat pump to condition that extra space. I've shown him what articles I have found that talk about being able to downsize a system once ccSPF is installed. I used the "thermos bottle" analogy to no avail. He thinks it is a great idea for cathedral ceilings, but not attics. Is there any real data,tests,documents etc that will allow me to speak more confidently on this? Thing is, I believe if we helped him understand how this works to his benefit he would start promoting this application to his customers. We spray BASF spraytite 178 in the Pacific Northwest.

Posted: Jul 21, 2010 06:16 AM

he may be right...
there is a good article about this in sprayfoam mag from spfa.org...i think it was the most recent issue...(not a member,,join,,be,,all that you can be,,,tell em 'dude sent ya),,,
a brief synopsis...in some of these attics you are adding more cubic feet of "passive conditioned space" to the load than the "active conditioned space" below...but load is load none-the-less,,(physics is fizzics),,and a savey hvac contractor,,,one who does load calculations to size his equip,,,will recognize this additional load and size accordingly...you may want to seal at the level of the drywall ceiling in some of these applications...
hope this hillbilly explanation helps..
dude :)

mason

Posted: Jul 21, 2010 08:47 AM

There are some very good articles on unvented attics at Building Professional Consortiums website. Or just email me and I will forward them to you.

masonknowles@aol.com

Alex Ek

Posted: Jul 21, 2010 04:36 PM

Thank you Dude and Mason. I met with another HVAC contractor today and had him run his heat load calculations ( some piece of software he has )on a typically 4/12 pitch roof 1400 sq ft attic space which is common around here and according to his numbers a two ton system ought to be sufficient where without the foam a three ton system would be required. I know this won't work for every application but it is helping build a case for this issue. Do you guys feel it would be a benefit to do a calculation like this on each attic system to determine if we should spray the roof deck or the drywall ceiling? Mason I know your ceiling was sprayed and you seem to like it, was that at your request or did it make more sense to do it that way vs. the roof deck for other reasons? I will email you for those articles.

mason

Posted: Jul 22, 2010 10:54 AM

At the time I insulated my attic, I had no choice. In 2003, building codes in my area did not allow unvented attics so I was forced to spray the foam on the floor of the attic. I would have preferred to spray the underside of the roof deck since I had tons of ducts in the attic. So, I added another layer of insulation on the ducts, it seemed to help. At the time, I couldn't spray the ducts with foam, which you can do now.

I sold the house last year, so I guess it will stay the way it is.

My wife incidentally was complaining last year that our energy bills had not gone done from before we had the attic insulated with foam. I reminded her that they had not gone up since 2003 even though energy costs have gone through the roof since then.

Now we bought a house in Savannah that has only fiberglass insulation. And last months electric bill was $380 for a 3000 sq ft house. Guess I am going to have to spray some foam in it next year. Have to save up my pennies first.

You need to login to reply to this topic. Please click here to login.