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  1. #1
    Join Date
    Apr 2012
    Location
    Princeton NJ
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    125

    How much make up air?

    Hi,
    I would love any help you could give me with regards to deciding how much make up combustion air i need for my master bedroom area. The natural gas, room air fed units are a 90% 80k btu furnace (oversized), and two (overkill) 50 gallon hot water heaters, in a 700 sq ft unfinished basement (insulated ceiling).

    It connects via an open 3/4 door passage to an area where my wife works out (rarely i must add). There were two screens in place of concrete blocks for vents in the equipment room. In winter the equipment area is freezing cold, and the cold drifted over to my wife's workout area. I perhaps stupidly sealed off the two screen vent/holes.

    I would love to have the minimum safe air possible. What would i need in winter? Maybe just one open. What about summer (only the hot water heaters).

    Thanks

    Steve

  2. #2
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
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    5,062
    Quote Originally Posted by central nj View Post
    Hi,
    I would love any help you could give me with regards to deciding how much make up combustion air i need for my master bedroom area. The natural gas, room air fed units are a 90% 80k btu furnace (oversized), and two (overkill) 50 gallon hot water heaters, in a 700 sq ft unfinished basement (insulated ceiling).

    It connects via an open 3/4 door passage to an area where my wife works out (rarely i must add). There were two screens in place of concrete blocks for vents in the equipment room. In winter the equipment area is freezing cold, and the cold drifted over to my wife's workout area. I perhaps stupidly sealed off the two screen vent/holes.

    I would love to have the minimum safe air possible. What would i need in winter? Maybe just one open. What about summer (only the hot water heaters).

    Thanks

    Steve
    How many BTU are the two HWH?

  3. #3
    Join Date
    Apr 2012
    Location
    Princeton NJ
    Posts
    125
    Second opinion, thanks. Not sure. They are 50 gallon. Standard type, bradford white i believe. Not super efficient or anything.

  4. #4
    Join Date
    Apr 2012
    Location
    Princeton NJ
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    I can check tonight if that helps.

  5. #5
    Join Date
    Mar 2009
    Location
    Mount Holly, NC
    Posts
    3,512
    so, basically you have 170Kbtuh of gas appliance input. you will need to supply air to. there also needs to be a HIGH and a LOW combustion air source.
    The TRUE highest cost system is the system not installed properly...
    The three big summer hearththrobs...
    Mel Gibson
    Dwane Johnson
    The A/C repairman

  6. #6
    Join Date
    Apr 2012
    Location
    Princeton NJ
    Posts
    125
    Well would two, or preferably one, screens instead of block be enough? (16x8 each i'm guessing). It would be about 25 feet away, and certainly not low and high.

    I guess i wouldn't care if I could put a door to the room, but there are the water pipes and the water heaters. The room gets its heat passively mostly from the other room, (which gets it from lack of insulation b/t the study above). A stupid arrangement.

    thanks
    Steve

  7. #7
    Join Date
    Apr 2012
    Location
    Princeton NJ
    Posts
    125
    Another question would be what would i need for only the hot water heat. I will eventually replace the 80k with a 40k york modulator.

  8. #8
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
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    Quote Originally Posted by central nj View Post
    Another question would be what would i need for only the hot water heat. I will eventually replace the 80k with a 40k york modulator.
    You stated the furnace is a 90%, is it piped to the outside both inlet and outlet? And what is the btus on the HWH?

  9. #9
    Join Date
    Apr 2012
    Location
    Princeton NJ
    Posts
    125
    Second Opinion, thank you.

    Both HWH are 40k each, total of 80k. The furnace is 80k.

    Perhaps not relevant, but the space is 1,000 sq ft (maybe 1500 is you include the non-insulation/drift to part of the basement.) So the furnace is only running in short bursts. The hot water heaters are for the "whirlpool" tub, which is never used, and the over the head huge shower rain-like head, also never used. It looks great in the ads, but water pouring straight down runs over the face and eyes, really not pleasant. But I guess it might be used so I should plan enough air for them both on full draw.

    Steve

  10. #10
    Join Date
    Apr 2012
    Location
    Princeton NJ
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    125
    Oh, the unit uses room air, but has a pvc pipe to vent. (a 1995 trane xe90).

  11. #11
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,428

    Exclamation 2006 INTERNATIONAL MECHANICAL CODE

    Quote Originally Posted by central nj View Post
    Hi,
    I would love any help you could give me with regards to deciding how much make up combustion air i need for my ... /// residence
    Thanks

    Steve
    http://www2.iccsafe.org/states/newje...tion%20Air.pdf

    DO IT RIGHT AND DO IT COMPLETELY RIGHT.!
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  12. #12
    Join Date
    Apr 2012
    Location
    Princeton NJ
    Posts
    125
    dan sw fl:
    Thanks! 1995 construction, w/dryvit on the exterior walls (super tight), but no spray foam or anything special in the attic or basement area. Would you agree that i'm "not unusually tight".

    If that's the case, i could leave it as is, no outside air. The 3/4 door size passage way is more than 1 sq inch/1k btu. To be safe may I will leave a 7x7 inch opening in the block screen (1 sq/4k btu).

    Thanks

    Steve

    Thanks.

  13. #13
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
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    5,062
    Quote Originally Posted by central nj View Post
    dan sw fl:
    Thanks! 1995 construction, w/dryvit on the exterior walls (super tight), but no spray foam or anything special in the attic or basement area. Would you agree that i'm "not unusually tight".

    If that's the case, i could leave it as is, no outside air. The 3/4 door size passage way is more than 1 sq inch/1k btu. To be safe may I will leave a 7x7 inch opening in the block screen (1 sq/4k btu).

    Thanks

    Steve

    Thanks.
    You should be fine as is since the room communicates with the rest of the basement, and you could pipe the intake to the furnace to the outside as a quick reduction .

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