Fresh air for the furnace.

Originally Posted By: rkulla
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I was inspecting a 5 yr old townhouse this week. The ceiling in the mechanical room was finished off. There wasn’t a fresh air intake in the room. The duck work was in the attic, and pretty much covered with insulation. No walking boards in the attic, about 18" of insulation. I talked to my brother who is a heating contractor about it. He said that at times they do add it directly into the return air. That’s what I was thinking. I wrote it up as fresh air for the furnace not visible due to the ceiling being finished off, with a comment that it can be added directly into the return air supply. Comments?? PS the furnace wasn’t a high efficiency one.



Rex Kulla


Custom Home Inspections


Maple Grove, MN


(612) 799-3093

Originally Posted By: Greg Owens
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huh, what did he say? icon_question.gif if you are talking about cumbustion air how would the air get from the return plenum to the combustion chamber, unless maybe it is an open air return through the door. you never came out and said it was a gas furnace but I will assume it is. it just doesn’t sound right.


Originally Posted By: Blaine Wiley
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Rex,


Are you speaking of a fresh air intake, or of a combustion air intake?


Originally Posted By: dvalley
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Rex,


Are you saying that this furnace has no return air intakes throughout the house? Or just in the basement area?![](upload://aknpuDfhccrZKRyjQTQQ4l0sais.gif)


If you are referring to a return register in the basement only, then I wouldn't worry about it.

It's not a good idea to take return air from the same room the furnace is installed. If the furnace ever developed incomplete combustion or didn?t burn properly, this could cause Carbon Monoxide to spread throughout the living area of the house very rapidly.

If the basement is finished, you will see return grilles in the finished areas only, but the furnace should be in a closed-in area with induced draft taking outside air.

Returns can be anywhere else except the furnace room.



--
David Valley
MAB Member

Massachusetts Certified Home Inspections
http://www.masscertified.com

"Some cause happiness wherever they go; others, whenever they go."

Originally Posted By: rkulla
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Sorry guys, it is a slab townhouse. Yes it does have return air ducts throughout the house. Yes it is a gas furnace. I am referring to the outside air supply.



Rex Kulla


Custom Home Inspections


Maple Grove, MN


(612) 799-3093

Originally Posted By: dvalley
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Quote:
I wrote it up as fresh air for the furnace not visible due to the ceiling being finished off, with a comment that it can be added directly into the return air supply.


You will not get combustion air from the return air supply! ![](upload://yehyMS8bacC3j7qtIevbtkNCVM.gif)

The air coming in from the return ducts will be drawing house air that has cooled, and brings it back to the furnace to be reheated and recirculated.
This indoor return air will then flow around the heat exchanger to be heated and then circulated throughout the house through the return ductwork.



--
David Valley
MAB Member

Massachusetts Certified Home Inspections
http://www.masscertified.com

"Some cause happiness wherever they go; others, whenever they go."

Originally Posted By: rkulla
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Hey Dave,


Yes, it is a conventional furnace in a mechanical room. I talked to the city inspector today, he said that is is ok to have the fresh air piped directly into the return air supply. You don’t see it that often. Some manufacturers require a certain amount of length from the furnace where it is installed. One problem can be condensation in the return. I agree that it will not directly give the furnace combustion air, but I guess indirectly it will into the home. eusa_think.gif



Rex Kulla


Custom Home Inspections


Maple Grove, MN


(612) 799-3093

Originally Posted By: phinsperger
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rkulla wrote:
. Some manufacturers require a certain amount of length from the furnace where it is installed. One problem can be condensation in the return. ![eusa_think.gif](upload://lNFeGuTetUAtwNVgUSOuUzgrGGK.gif)


In cold regions, the temp differance to the heat exchanger can be significant and cause stress on it ... crack ! Thus the required length from the furnace to give the outside air a chance to mix properly with the return air


--
.


Paul Hinsperger
Hinsperger Inspection Services
Chairman - NACHI Awards Committee
Place your Award Nominations
here !

Originally Posted By: rkulla
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That’s correct, in fact there can be condensation issues that could prematurely rust out the exchanger too.



Rex Kulla


Custom Home Inspections


Maple Grove, MN


(612) 799-3093

Originally Posted By: Blaine Wiley
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I think most areas now and maybe for about the last five years or so require a fresh air (from outside) intake into the return air system. Houses are being built so tight that the clothes dryers, stoves, bathroom exhaust fans, etc. can use up available house air. The fresh air intake resupplies air to the home and actually makes a “healthier” house. There is usually a vent on the exterior of the home which looks similar to a dryer or bathroom fan exhaust duct cover.


Originally Posted By: cbottger
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rkulla wrote:
I was inspecting a 5 yr old townhouse this week. The ceiling in the mechanical room was finished off. There wasn't a fresh air intake in the room. The duck work was in the attic, and pretty much covered with insulation. No walking boards in the attic, about 18" of insulation. I talked to my brother who is a heating contractor about it. He said that at times they do add it directly into the return air. That's what I was thinking. I wrote it up as fresh air for the furnace not visible due to the ceiling being finished off, with a comment that it can be added directly into the return air supply. Comments?? PS the furnace wasn't a high efficiency one.

You guys are scaring me. Sure hope your brother never installs heating systems near me. Make up air is installed in Return air ducts only on light Commercial public buildings for proper air change. Residential units are a sealed loop between supply and return air. Combustion air for the burner of a gas fired furnace to comply with modern day codes must be supplied from an external source such as an attic. You will Normaly find two ducts installed in the ceiling of the furnace room traveling into the attic one protrudes into the room 18 inches from the top of the ceiling the other duct is 18 inches from the floor as this allows for proper combustion air for the burner.


Originally Posted By: jpeck
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I think there is confusion because of incorrect and inconsistent terminology.


Outside air.

Fresh air intake.

Return air.

Make-up air.

Combustion air.




Outside air can be either 'fresh air make-up air', which is typically run through a heat exchanger to the air in the conditioned space, or, it can be 'combustion air' (such as when the furnace is located in a "confined space"). Both are 'outside air'.

Return air is that air which is circulating back to the air handler. 'Fresh air make-up air' can be run directly into the return air (again, usually through a heat exchanger).

Combustion air is that air used for combustion, and, when the gas appliance is located in a "confined space", needs combustion air. This can be from outside through properly sized and located openings, or through a transfer duct or opening which is properly sized to allow the "confined space" to communicate with the non-confined space sufficiently so that the "confined space" is no longer 'confined space'.


--
Jerry Peck
South Florida

Originally Posted By: Ryan Jackson
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More importantly than the confined space issue would be the unusually tight construction issue, which trumps confiend space. If this house was built in the last five years, you need combustion air. There is no getting around unussualy tight construction. icon_sad.gif



Ryan Jackson, Salt Lake City