Another gas furnace in a closet question...

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Another gas furnace in a closet question...

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Joe Funderburk
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Posted: Nov 25, 2005 11:56 PM       Post Subject:

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OK, I'm a slow learner.

Here's another gas furnace in a closet from today's inspection. It was a Ducane--model number was illegible. "Direct vent forced air" furnace.

Here's what puzzles me: an opening was on top of the unit where I think the PVC pipe for combustion air should be secured--it was not there. You could see the flames clearly through this opening. The return was on bottom left of the unit--no duct to outside; also drawing air from inside closet. The closet door was louvered, but the top section of the louvers was covered. The lower part of the closet door had a filter installed. There is no other entry for combustion air--all air comes in through the filtered door.

It seems to me that if all the combustion air comes in through the filter this is incorrect. Doesn't the return air and combustion air mix because of this arrangement? Even if there was sufficient louvered area, is it OK to have the return air and combustion air mixed together in a closet???

I appreciate your help. HVAC isn't my strong suit.

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David Valley

Certified Massachusetts Home Inspections
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Posted: Nov 26, 2005 5:33 PM       Post Subject:
Joe,

A furnace can not draw return air from the same room/closet that the furnace is installed.

A return duct must be installed from the lower left side of this particular furnace cabinet and run into a wall opening with an outside grill within this room, which will force this furnace to draw return air from another room.

Without a return duct, if this furnace were to give off CO (due to an improper burn), it would allow the deadly gases to get sucked into this return and would rapidly send these deadly fumes throughout the living area. Not Good.

As for that combustion air piping missing on top of the cabinet, I'd write it up as not installed. I see this sort of installation quite a bit. Not a major issue but I'd advise client that this furnace would be much safer drawing outside air verses conditioned air.

Where's this furnace located within the house?

--
David Valley
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Massachusetts Certified Home Inspections
http://www.masscertified.com

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

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Joe Funderburk
NACHI Member: No
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Posted: Nov 27, 2005 4:44 PM       Post Subject:

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Thanks so much for your reply. To answer your question, the furnace was about in the center of the home, in a hallway closet. It was a 100,000 BTU unit for a 2 bedroom 1500 sq. ft. condo. When you open that closet door, you better hold on tight, because the furnace would suck it shut if you didn't. Here's how I worded my report:

" The gas furnace in the closet is not thought to be installed correctly. All the return air and combustion air enters the closet, where the furnace is located, through a 22? x 27? filtered opening in the closet door. Normally, the return air is ducted directly to the furnace and the combustion air is unfiltered and drawn in from outside. An opening at the top of the furnace is designed for combustion air intake from the outside, but it is not utilized. A louvered section of the door has been closed off. Combustion air (?make-up air?) is required for gas burning appliances at a rate of 50 cu ft / 1000 BTU or else external ventilation is required (no external ventilation was provided for this room other than the filtered opening mentioned above). (Sizing calculations were not made by the inspector.) Also, the unit is 100,000 BTUs and may be oversized for the home.
It is recommended that a licensed HVAC contractor evaluate the unit and make repairs, if any, as deemed necessary. He/she should specifically address the following issues:
A. Is there sufficient combustion air provided and is the source of combustion air (from inside the home) satisfactory.
B. Is the volume of return air satisfactory.
C. Is the unit appropriately sized for the home."
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David Andersen

David A. Andersen & Associates
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User: dandersen
Posted: Nov 28, 2005 1:15 PM       Post Subject:
The return air register (none in this case) must be 10 feet from the furnace burner intake.
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Patrick Bolliger

Home Site Inspections
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Posted: Dec 8, 2005 12:14 PM       Post Subject:
Joe,

That install is an example of how an install should NOT be made.

The MFG. has installation instructions for any FAU and it should be followed with and exceptions that the local AHJ may modify.

Should any other type of install NOT follow the MFG. instructions you can get a Death machine .. pure and simple when it come to burning Natural gas.

I see several clue in your pictures in addition to your notes that this install is just plain STUPID and dangerous..

Remember a 10:1 air to gas ratio is needed for a complete gas burn..


The number one thing is MFG. instructions, followed by any AHJ mods.

You can verify what type of category appliance it is by the name plate (usually inside the unit) ..

Cat 1 & 2 are Natural draft units (negative pressure) (with metal, single walled flue, usually) and have draft hoods.. These puppies need major air space.. Per btu's You see the metal flue coming out from the draft hood.
They should NEVER be inside a closet without proper combustion air supply since this can be CO generators.. Even in basements that are finished after new construction can be a problem when the air space gets closed off in a smaller "room"..

Cat 3 Positive pressure Mid efficiency 80% ish systems can have open burners and a vent assisted fan unit... Metal flues (depends on MFG.) , doubled wall (still take room air for combustion air needs... Same needs like Cat 1 & 2 with respect to combustion air requirements.

Cat 4 positive pressure 90% + units, sealed burners, PVC pipes Per MFG. take combustion air from the outside into the house.. Why any one uses inside air for these is just plain stupid... Not per MFG. instructions... could void any warranty and decrease efficiency..

You cannot mix appliances of cat 1 -2 natural draft / negative pressure and cat 3-4 positive pressure . Examples are a negative pressure water heater and positive pressure FAU into a chimney...
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John Rupert

Solitaire Heating & Cooling HVAC Mechanical Inspection Service
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Posted: Dec 11, 2005 12:24 PM       Post Subject:
Joe,
From the picture I can not determine of the left side of the furnace is cut out for return air, if it is not then the return air ducting is entering the bottom of the furnace from below the floor I see this type of installation all the time. The home owner likely closed off the louvered door because the noise was too loud, he put a filter in the bottom half to control the dirt, The danger here is the reduced combustion air from the blocked louvers and if the filter becomes clogged it too will reduce or stop air flow, causing incomplete combustion. Combustion air can be provided by one or several methods, and in many code areas the louvered door is all that is required.

The lack of combustion air piping will depend on the manufacture of the furnace, many what they call a one pipe where the intake pipe is optional Only the furnace designed as a two-pipe system must be piped to the out side. Be careful quoting air flow quoting combustion air ratios, they will be different for each manufacture, for each model for induced draft or for natural draft, this could get you into trouble.

John Rupert
Accurate Property Inspections
Solitaire Heating & Cooling
CSG Training (HVAC Training & Consulting)
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John Rupert

Solitaire Heating & Cooling HVAC Mechanical Inspection Service
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Posted: Dec 11, 2005 12:29 PM       Post Subject:
Also combustion air and make up air are two different terminologies in the HVAC industry that do not mean the same

Combustion air is divided into four types depending upon its role and the design of the particular burner. Primary, secondary, excess and dilution air and is for the sole purpose of supporting combustion

Make up air is when air taken from the building is replaced, normally in commercial buildings, more info http://www.marsair.com/mkupair1.htm

John Rupert
Accurate Property Inspections
Solitaire Heating & Cooling
CSG Training (HVAC Training & Consulting)
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Russell Meyers

Home Inspection Services, Inc.
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Posted: Dec 16, 2005 2:03 AM       Post Subject:
Joe,

I had one of these Ducane units a while back also. In retrospect, i'm not sure it qualifies as a true direct vent unit since you can see exposed flame within the unit? It does have a fan assisted vent with optional exterior combustion air supply to the cabinet, but it is not to an enclosed or sealed combustion chamber, if I remember correctly? Anyway, in both cases the outside air intakes were not utilized which seems like a waste.

John is correct that we shouldn't quote our calculations to clients, (then they see us as the experts) but we should have rule-of-thumb calcs that will help substantiate our concerns and know when to recommend professional services.

It appears to me that the original builder installed a louvered door that was adequate for providing the needed combustion air to the furnace. But the modifications to the door, for whatever reason, has created an unsafe condition.

Combustion air required: 1 sq. in. / 1000 BTU for grille size = 100 sq. in. / grille x 2 grilles (1 High & 1 low) = 200 sq. in total free air flow.
Actual Combustion Air provided: 22" x 27" = 594 sq. in. x .25 factor for actual free air flow area of wood louvers = 148.5 sq. in. (also less affects of filter restriction)


These calculations, in my case, would be a red flag for immediate professional evaluation by a qualified heating technician. (Especially if, as you believe, the return air was also being drawn from with-in the closet)

I suspect the return air is routed through the floor, otherwise, by the guidelines I've been working with, the occupants should have been dead from carbon monoxide.

Peoples Energy Gas Co. in Chicago has a good CE course in gas appliances that I would recommend for those close enough to take advantage of it. NACHI recommended also I believe.

Just my thoughts, hope they help!!!

HAVE A GREAT DAY!!! icon_lol.gif icon_lol.gif icon_lol.gif

Russ Meyers
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