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Old 05-30-2020, 12:14 AM   #1
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Why 3 Transfer Grilles on Furnace Room Wall. Also do I need a cold air return?


Hi, I'm remodeling my basement and noticed the previous owner had 3 transfer grilles on the furnace room wall. I assume it's for better air flow to the furnace. But several years ago when I had a water heater replaced, they installed a duct leading from outside to the furnace room (I believe it's called a combustion air duct?). My question is whether these 3 transfer grilles are needed - 0,1, 2 or all 3?

I was also wondering if I need a cold air return in this basement. There are no doors - just an open stairway leading to the cold air return upstairs? I'm considering converting one of the transfer grille to a cold air return if needed - although hoping I don't need to do the extra work if not needed!
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Old 05-30-2020, 06:35 AM   #2
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Re: Why 3 Transfer Grilles on Furnace Room Wall. Also do I need a cold air return?


Both the water heater and the furnace may have combustion air needs. Since we have no idea what units you have and other details it is hard to advise. I'm not a hvac pro but work with energy functions and we avoid starving any appliance for combustion air, it can cause backdrafting of either one. Since the water heater has the least need I wouldn't conclude that outside air supply will serve both.

Some pictures might help and include the new outside air supply.

pros will be along.

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Old 05-30-2020, 11:19 AM   #3
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Re: Why 3 Transfer Grilles on Furnace Room Wall. Also do I need a cold air return?


Quote:
Originally Posted by Bud9051 View Post
Some pictures might help and include the new outside air supply.
Here are pics. The furnace is old - will be replaced I suspect in a few years. The door for this furnace room is a bifold, so it does not seal the room off as much as a standard door.

BTW: the pics are not rotated correctly in this forums but they are correct on my PC. Not sure how to fix.
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Old 05-30-2020, 12:44 PM   #4
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Re: Why 3 Transfer Grilles on Furnace Room Wall. Also do I need a cold air return?


The safest decision is to leave them alone. If you must get rid of them, I recommend getting a louvered door to replace the bifold. I'd probably do that anyway. Those methods are more reliable than an outside air duct run. That's a large water heater and if you have 60k or 80k of furnace demand to add to that, it's best to not risk choking it.

I recommend installing an air return in the basement. Down low is where I like them but up high is better than nothing. Even with an open door to upstairs, the basement air flow is never adequate without a RA of its own. It'll smell like a basement without one so that's the tip off.
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Old 05-31-2020, 06:33 AM   #5
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Re: Why 3 Transfer Grilles on Furnace Room Wall. Also do I need a cold air return?


Looks like combustion air intakes for the furnace.
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Old 05-31-2020, 07:09 PM   #6
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Re: Why 3 Transfer Grilles on Furnace Room Wall. Also do I need a cold air return?


For heating you should install returns. Otherwise the heat will hug the ceiling and find its way upstairs, leaving your cellar cold.
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Old 05-31-2020, 07:34 PM   #7
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Re: Why 3 Transfer Grilles on Furnace Room Wall. Also do I need a cold air return?


leave the grills alone, definitely add return air to the basement.

You should really have the heat exchanger in that old furnace checked, if it's 20+ years old very good chance it's cracked.

Best to go with sealed combustion 90%+ when replacing.
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Old 05-31-2020, 11:15 PM   #8
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Re: Why 3 Transfer Grilles on Furnace Room Wall. Also do I need a cold air return?


Thanks for the replies.

Here's my plan. I will leave the upper and lower right transfer vents alone- along with the more recently added fresh air combustion duct in the furnace room, that should be enough for the furnace and water heater. I'll convert the lower left transfer vent to a cold air return for the basement family room

Sound good?

User_12345, I had the furnace checked last summer - no cracks. But will be replacing in the next couple of years anyway - I believe it's from the early 90's.
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Old 06-01-2020, 08:56 PM   #9
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Re: Why 3 Transfer Grilles on Furnace Room Wall. Also do I need a cold air return?


I just have to add:

A CO and smoke detector is an excellent safety measure for basements with gas consuming devices operating, especially if there will be people sleeping in there. Code also has egress requirement that you should review, especially if it's not a walk-out basement and also if you intend to partition off any rooms, each must have egress windows.
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