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-   -   Combustion (make-up) air in basement (http://www.diychatroom.com/f17/combustion-make-up-air-basement-34632/)

tthacke 12-29-2008 02:31 PM

Combustion (make-up) air in basement
 
Hello,
I am about to start remodeling my basement and have a few questions regarding allowances for combustion air. The house is about 13 years old in the Chicago suburbs. According to all my calculations, I will need 6,400 cu ft. for combustion air. Becasue the mechanical room containing my furn. & w/h is not large enough, I intended on using louver doors to tie in air from the rec room. Even in this situation, I will be 400 cu ft short due to the planned ceilings in the rec room. I will be short regardless of if I use a suspended ceiling or dry wall. The way I look at it, I have two options. 1) leave the ceiling unfinished and paint the entire ceiling or 2) install an outside combustion air kit to my mechanical room.

I was hoping somebody would be able to give me some advice/opinions on my situation. Also, if I decide to install the outside kit, is there any information you could pass along as to how to do it, where to find one? I have only been able to find very limited information and no complete kits or instructions. Any web links in installation instructions would be greatly appreciated.
Thank you in advance.

SKIP4661 12-29-2008 03:19 PM

Seems like a lot of combustion air. From what I have seen, typically a 6 inch or 8 inch round duct piped to the outside is the norm for residential mechanical rooms.

yuri 12-29-2008 05:12 PM

How many BTU's are the water heater and furnace rated for. Generally we use 1 sq ft/100,000 Btus.

hvaclover 12-29-2008 05:34 PM

I am reading the specs for bringing in some outside air to supplement the your slight deficit.
A 4" round is good for up to 40k btu. A factory made make up air would cost more than 4 lengths of 4" pipe and an outdoor dryer-style fresh air intake.

tk03 12-29-2008 05:57 PM

See the following link to amount of combustion air required by national code. Your local code may require more.
The only required make up air needed is the difference of what is needed minus what you have. Is the basement area to to upstairs an open doorway or does the doorway have a door at the top of the stairs.
http://www.comfort-calc.net/Combusti...lculation.html
There are a few ways to get what is required.
I can supply options once you answer the above questions.

tthacke 12-29-2008 08:35 PM

Thank you all for your help. Below are answers to the questions asked.

The furnace is 88,000 btu and the water heater is 40,000 btu...for a total of 128,000 btu. 128,000 / 20 = 6,400 cu. ft. required for the combustion air. While I will have a door to the mechanical room/crawl space, it will be a louver-type to draw in air from the rest of the basement (i.e. the rec room). After putting a ceiling on the rec room only, my total air volume is 6,020 cu. ft.

Regarding the stairway, I will have a door at the top that will need to be closed.

I hope this better helps to lay out the situation. Thank you all again.

hvaclover 12-29-2008 09:43 PM

If you want to provide fresh air for all your combustion needs instead of just running the right sized pipe to make up the difference your free space is lacking you will need a six inch pipe.

http://img381.imageshack.us/img381/4...pairor9.th.gif
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tthacke 12-30-2008 07:06 AM

Thanks hvaclover. If I run that pipe/hood (similar to the picture you included) into the basement, do I need to put an extension of flex on it to run it to the ground, or can I just leave the 6" pipe sticking out of the wall?

hvaclover 12-30-2008 10:46 AM

First off buy afresh intake that has a screen in it goes outside. You then terminate the six inch pipe twelve inches above the floor. Use hard pipes made of 26ga steel.

Also add insulation to the pipe drop avoid sweating.

The kit I showed you would cost about$200.

But it connects to the cold air return. The hood vent and six pipe is a much better option.

tthacke 12-30-2008 11:00 AM

I understand. Thank you. Should the end of the pipe be terminated into a disfuser or anything? I've read about running them into a 5 Gal bucket.

I have about 12' from my outside wall to the furnace. Can the pipe drop along side the wall, or does it need to be taken closer or a horiz. path to the furnace before it drops?

I apologize for all the questions, I just want to make sure I have all the information.

hvaclover 12-30-2008 12:07 PM

Quote:

Originally Posted by tthacke (Post 204331)
I understand. Thank you. Should the end of the pipe be terminated into a disfuser or anything? I've read about running them into a 5 Gal bucket.

I have about 12' from my outside wall to the furnace. Can the pipe drop along side the wall, or does it need to be taken closer or a horiz. path to the furnace before it drops?

I apologize for all the questions, I just want to make sure I have all the information.

No what you describe is fine and more than close enough
I just strap them to the wall and leave the bottom open with no other fitting.

I would suggest maybe chicken wire just in case. A five gallon bucket would create it's own pressure zone, unless I miss my guess. That would impede the full air flow.

I could see a five gallon bucket with several one inch holes drilled around the bucket from bottom to top.














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