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Jurgen Hartwig Posted: Aug 14, 2007 06:43 PM	Unvented attic - sealed furnace and gas water heater I bought a home that was partially rebuilt after a 2nd story fire. The home is essentially a shell (raw framing) with new electrical, plumbing, and HVAC. I have been trying to get advice locally, but Memphis, TN is woefully behind in SPF. I was aiming for an unvented attic to create a whole house envelope. However, I have been advised (by one, perhaps the only SPF contractor servicing Memphis) I need sealed combustion chambers on my gas furnace and water heater, which would require complete replacement of the existing 18 month old, never used hardware. It appears there is no way around this requirement, as make up air must be separate from the living space. I cannot justify the expense of replacing the 3 80% efficient furnaces and 2 water heaters with 90% efficient, closed combustion systems. The payback time would be very long. Am I off track? It appears my best route is SPF or sprayed cellulose in the walls and blown cellulose in the ceiling. regards, Jurgen
Terry Adams Posted: Aug 14, 2007 09:46 PM	Unless I don't understand what furnace or hot water heater you have up there but if your furnace and hot water heater is located closet I would think all you need is to install is a vent from outside. Thats the way AC guys do it down here, combustion air comes thru a vent in the roof in most cases.
Jurgen Hartwig Posted: Aug 14, 2007 10:17 PM	I apologize for the confusion. The HVAC equipment and gas water heaters are in the attic. The equipment pulls air for combustion from the attic space. I need to consult with a few more HVAC contractors for guidance.
Posted: Aug 15, 2007 09:00 AM	You must have combustion air for the equipment, if these are naturally aspirated units then build an enclosure around them and bring the outside air into the "closet" with ductwork, preferable pipe. Surely there is an AC contractor in Memphis that will know what to do. Kenneth
Scott Snyder Posted: Aug 15, 2007 06:40 PM	I've worked in Memphis and Shelby County during the 90's in the HVAC industry. Best advice is to contact the building inspectors. If JB is still there he used to work with us on special situations. Memphis has some "special" HVAC requirements that are more strict than the state mechanical code. Easier to find out on the front end what they want vs. tearing out and fixing later.
Jurgen Hartwig Posted: Aug 15, 2007 10:11 PM	Thanks much. I did a lot of searching at hvac-talk.com, and it appears you guys are correct. Using the 80% efficient furnaces would require enclosing the units in "closets" with ductwork providing air for combustion. Due to the layout of the attic space, I feel the benefits don't justify the extra work. My brother has already met and spoke to a local inspector. When asked about SPF, the inspector said he had only seen an unvented attic space once in his years, and that first time was only a few months ago. I would guess the number of unvented attics in Memphis number less than 100. I'm beginning to think this road (unvented) is not one I should try to travel. Had the house already 90% furnaces with sealed combustion, I'd be thinking differently. Eventually, I will run my thoughts by my preferred HVAC contractor. Right now, though, temps have been well over 100 every day, and I know he's working overtime.
Terry Adams Posted: Aug 15, 2007 11:26 PM	Roof deck is the most efficent, but you can still spray foam in the walls and down on the sheetrock ceilings. You will be very happy and it will money well spent. You are on the right site for the best information. Back in the day microwave oven in houses were very rare too.
Terry Adams Posted: Aug 15, 2007 11:26 PM	Roof deck is the most efficent, but you can still spray foam in the walls and down on the sheetrock ceilings. You will be very happy and it will money well spent. You are on the right site for the best information. Back in the day microwave oven in houses were very rare too.
Posted: Aug 16, 2007 08:37 AM	Sounds to me like I outta start a SPF operation in Memphis!!! From direct involvement with both new construction and retrofit foam work I promise you foam is worth at least 2 times what you will pay for it. Kenneth PS: 95% efficient furnaces are great! Think of it this way, 80% furnaces heat you with 80 cents of each dollar and 95% furnaces use 95 pennies of each dollar for heating your home.
Jurgen Hartwig Posted: Aug 16, 2007 01:15 PM	The contractor I met was really down on Memphis and SPF. He said the homebuilders and homeowners are too cheap. He has enough problem selling sprayed cellulose at 20% over the cost of fiberglass, much less up-selling to SPF at 2.5 times the cost of fiberglass. The contractor stated he cannot justify a spray crew to work Memphis exclusively. He does work for West TN and middle TN, including Nashville. It really is disappointing. $500-700k homes are still being built with fiberglass insulation. I considered upgrading to higher efficiency HVAC equipment, but I'd rather put the money into better insulation. 95% efficient furnaces do little good when the house leaks like a sieve, and my budget would get blown away if I did SPF and better HVAC equipment. I figure I can always upgrade HVAC later, but I can never upgrade insulation.
Jason Davis Posted: Aug 16, 2007 04:24 PM	Jurgen, We are located in Birmingham, AL and are will to make the drive to Memphis. We offer 2lb closed cell and 1/2lb open cell. We do NOT limit ourselves to just one area. Please give us a call @ (O)205-424-3171 or (C)205-368-1226. We would be happy to talk to you and work out a deal. Thanks, Jason
Dave Strnad Posted: Aug 19, 2007 05:20 AM	turbo6bar, I realize things are different everywhere, but where I live the whole attic is considered a closet. This also applies to basment, crawl space, etc. As long as your not using the attic as living space. Any inspector should be ok with you running combustion air near each furnace. Our codes just changed and now it dosen't even have to be run to each unit, we just have to dump it somewhere in the same room. Any decent mechanical contractor should be able to fiqure out how much combustion air you need. I would put together a plan of what your going to do and submit it to the inspector, it sounds like maybe there is a misunderstanding.
Posted: Aug 19, 2007 04:37 PM	I have shot more than one "budget". I know first hand how good foam is and would not build a dog house without spray foam! I retrofitted my own house just like you are describing. I will be changing the old furnace out before winter to a 96% furnace. I did have to reduce the condensor on full ton due to humidity control problems. That being said, the electrical KW consumption was down over 40% in June this year over the previous 2 years June usage. LEAKY house, single pain windows, sliding glass 3 bay back porch entrance. Just letting you know that foam works. Houses have been insulated WRONG since we started building em. Kenneth
philip mullins Posted: Aug 20, 2007 09:51 AM	i dont know about where you live kenneth but, our electricity cost have risen about 12 percent from last year. so that 40 percent savings would be a very conservative number.
Posted: Aug 20, 2007 10:20 AM	troutkiller, I live in San Antonio, Texas. We have some of the cheapest KW rates in the country. Yesterday I was at a home we completed (unfortunately I was only the AC contractor on this home) over a year ago. Sprayed foam insulation, AC loads calculated by energywisestructures. Actually has better than 15 months of operation, submetered electrical service for the heating and cooling of the home. 23,600 +/- KW on the meter divided by 15 months = 1,573 KW per month. 4388 square foot conditioned space. How about that for energy efficiency? Got to love foam Kenneth
Jurgen Hartwig Posted: Aug 20, 2007 03:18 PM	Many thanks for the information, guys. I bought HVAC Calc over the weekend and just ran the numbers for the project house. The house will have 4400 square feet living space (conditioned). The driver for the cooling side is sensible load at 47k BTUs, which would call for around 5-5.5 tons. Existing equipment (3 systems totals 11.5 tons!!!). Still trying to work out the model for unvented attic space, but based on the calculations, I need to drop one complete unit and drop down to 2 units (upstairs and downstairs). I will get with the HVAC contractor this week and try to get some concrete plans laid out. I'm getting really excited about this project. Much of Tennessee has subsidized electricity, because of hydroelectric power on the TN River. My goal is electric bills under $140/month.

Author

Comments

Jurgen Hartwig

Posted: Aug 14, 2007 06:43 PM

Unvented attic - sealed furnace and gas water heater

I bought a home that was partially rebuilt after a 2nd story fire. The home is essentially a shell (raw framing) with new electrical, plumbing, and HVAC. I have been trying to get advice locally, but Memphis, TN is woefully behind in SPF.

I was aiming for an unvented attic to create a whole house envelope. However, I have been advised (by one, perhaps the only SPF contractor servicing Memphis) I need sealed combustion chambers on my gas furnace and water heater, which would require complete replacement of the existing 18 month old, never used hardware. It appears there is no way around this requirement, as make up air must be separate from the living space. I cannot justify the expense of replacing the 3 80% efficient furnaces and 2 water heaters with 90% efficient, closed combustion systems. The payback time would be very long.

Am I off track? It appears my best route is SPF or sprayed cellulose in the walls and blown cellulose in the ceiling.
regards, Jurgen

Terry Adams

Posted: Aug 14, 2007 09:46 PM

Unless I don't understand what furnace or hot water heater you have up there but if your furnace and hot water heater is located closet I would think all you need is to install is a vent from outside. Thats the way AC guys do it down here, combustion air comes thru a vent in the roof in most cases.

Jurgen Hartwig

Posted: Aug 14, 2007 10:17 PM

I apologize for the confusion. The HVAC equipment and gas water heaters are in the attic. The equipment pulls air for combustion from the attic space. I need to consult with a few more HVAC contractors for guidance.

Posted: Aug 15, 2007 09:00 AM

You must have combustion air for the equipment, if these are naturally aspirated units then build an enclosure around them and bring the outside air into the "closet" with ductwork, preferable pipe. Surely there is an AC contractor in Memphis that will know what to do.

Kenneth

Scott Snyder

Posted: Aug 15, 2007 06:40 PM

I've worked in Memphis and Shelby County during the 90's in the HVAC industry. Best advice is to contact the building inspectors. If JB is still there he used to work with us on special situations. Memphis has some "special" HVAC requirements that are more strict than the state mechanical code. Easier to find out on the front end what they want vs. tearing out and fixing later.

Jurgen Hartwig

Posted: Aug 15, 2007 10:11 PM

Thanks much.

I did a lot of searching at hvac-talk.com, and it appears you guys are correct. Using the 80% efficient furnaces would require enclosing the units in "closets" with ductwork providing air for combustion. Due to the layout of the attic space, I feel the benefits don't justify the extra work.

My brother has already met and spoke to a local inspector. When asked about SPF, the inspector said he had only seen an unvented attic space once in his years, and that first time was only a few months ago. I would guess the number of unvented attics in Memphis number less than 100.

I'm beginning to think this road (unvented) is not one I should try to travel. Had the house already 90% furnaces with sealed combustion, I'd be thinking differently.

Eventually, I will run my thoughts by my preferred HVAC contractor. Right now, though, temps have been well over 100 every day, and I know he's working overtime.

Terry Adams

Posted: Aug 15, 2007 11:26 PM

Roof deck is the most efficent, but you can still spray foam in the walls and down on the sheetrock ceilings. You will be very happy and it will money well spent. You are on the right site for the best information. Back in the day microwave oven in houses were very rare too.

Terry Adams

Posted: Aug 15, 2007 11:26 PM

Posted: Aug 16, 2007 08:37 AM

Sounds to me like I outta start a SPF operation in Memphis!!!

From direct involvement with both new construction and retrofit foam work I promise you foam is worth at least 2 times what you will pay for it.

Kenneth

PS: 95% efficient furnaces are great! Think of it this way, 80% furnaces heat you with 80 cents of each dollar and 95% furnaces use 95 pennies of each dollar for heating your home.

Jurgen Hartwig

Posted: Aug 16, 2007 01:15 PM

The contractor I met was really down on Memphis and SPF. He said the homebuilders and homeowners are too cheap. He has enough problem selling sprayed cellulose at 20% over the cost of fiberglass, much less up-selling to SPF at 2.5 times the cost of fiberglass.

The contractor stated he cannot justify a spray crew to work Memphis exclusively. He does work for West TN and middle TN, including Nashville.

It really is disappointing. $500-700k homes are still being built with fiberglass insulation.

I considered upgrading to higher efficiency HVAC equipment, but I'd rather put the money into better insulation. 95% efficient furnaces do little good when the house leaks like a sieve, and my budget would get blown away if I did SPF and better HVAC equipment. I figure I can always upgrade HVAC later, but I can never upgrade insulation.

Jason Davis

Posted: Aug 16, 2007 04:24 PM

Jurgen,
We are located in Birmingham, AL and are will to make the drive to Memphis. We offer 2lb closed cell and 1/2lb open cell. We do NOT limit ourselves to just one area. Please give us a call @ (O)205-424-3171 or (C)205-368-1226. We would be happy to talk to you and work out a deal.
Thanks,
Jason

Dave Strnad

Posted: Aug 19, 2007 05:20 AM

turbo6bar,

I realize things are different everywhere, but where I live the whole attic is considered a closet. This also applies to basment, crawl space, etc. As long as your not using the attic as living space. Any inspector should be ok with you running combustion air near each furnace. Our codes just changed and now it dosen't even have to be run to each unit, we just have to dump it somewhere in the same room. Any decent mechanical contractor should be able to fiqure out how much combustion air you need. I would put together a plan of what your going to do and submit it to the inspector, it sounds like maybe there is a misunderstanding.

Posted: Aug 19, 2007 04:37 PM

I have shot more than one "budget". I know first hand how good foam is and would not build a dog house without spray foam! I retrofitted my own house just like you are describing. I will be changing the old furnace out before winter to a 96% furnace. I did have to reduce the condensor on full ton due to humidity control problems. That being said, the electrical KW consumption was down over 40% in June this year over the previous 2 years June usage. LEAKY house, single pain windows, sliding glass 3 bay back porch entrance. Just letting you know that foam works. Houses have been insulated WRONG since we started building em.

Kenneth

philip mullins

Posted: Aug 20, 2007 09:51 AM

i dont know about where you live kenneth but, our electricity cost have risen about 12 percent from last year. so that 40 percent savings would be a very conservative number.

Posted: Aug 20, 2007 10:20 AM

troutkiller,

I live in San Antonio, Texas. We have some of the cheapest KW rates in the country. Yesterday I was at a home we completed (unfortunately I was only the AC contractor on this home) over a year ago. Sprayed foam insulation, AC loads calculated by energywisestructures. Actually has better than 15 months of operation, submetered electrical service for the heating and cooling of the home. 23,600 +/- KW on the meter divided by 15 months = 1,573 KW per month. 4388 square foot conditioned space. How about that for energy efficiency?

Got to love foam

Kenneth

Jurgen Hartwig

Posted: Aug 20, 2007 03:18 PM

Many thanks for the information, guys.

I bought HVAC Calc over the weekend and just ran the numbers for the project house. The house will have 4400 square feet living space (conditioned). The driver for the cooling side is sensible load at 47k BTUs, which would call for around 5-5.5 tons. Existing equipment (3 systems totals 11.5 tons!!!). Still trying to work out the model for unvented attic space, but based on the calculations, I need to drop one complete unit and drop down to 2 units (upstairs and downstairs).

I will get with the HVAC contractor this week and try to get some concrete plans laid out. I'm getting really excited about this project.

Much of Tennessee has subsidized electricity, because of hydroelectric power on the TN River. My goal is electric bills under $140/month.

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