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Old 11-03-2010, 05:10 PM  
willi5
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Default Unfinished Basement - Supply vs. Return

Hi,

While installing an HRV I recently had a cold air return added to my unfinished basement - in hopes to add some air movement to an old and sometimes damp area. The contractor added a 6" circular return from the inlet plenum across 6'-8' and down to 18" above floor level.

One 3" supply was already in place but had been taped off (obviously I removed the tape).

My question is does this setup result in a negative pressure in the basement which could pull moisture or gases through the concrete foundation?

We have recently noticed a significant increase in pink/white staining of the concrete (efflorescence or calcium deposit?) - I'd like to understand the cause before I try cleaning with vinegar, etc; When I had my HRV/Furnace contractor to come back and discuss with me, his comments were:

(a) the return/supply situation is not an issue - the return cannot pull more than is available to it (or at least that's what I think he was trying to say)

(b) the white/pink stains are calcium buildup that can be cleaned off

Perhaps it is related to the basement drying out with the installation of the HRV?



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Old 11-03-2010, 07:30 PM  
paul52446m
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Originally Posted by willi5 View Post
Hi,

While installing an HRV I recently had a cold air return added to my unfinished basement - in hopes to add some air movement to an old and sometimes damp area. The contractor added a 6" circular return from the inlet plenum across 6'-8' and down to 18" above floor level.

One 3" supply was already in place but had been taped off (obviously I removed the tape).

My question is does this setup result in a negative pressure in the basement which could pull moisture or gases through the concrete foundation?

We have recently noticed a significant increase in pink/white staining of the concrete (efflorescence or calcium deposit?) - I'd like to understand the cause before I try cleaning with vinegar, etc; When I had my HRV/Furnace contractor to come back and discuss with me, his comments were:

(a) the return/supply situation is not an issue - the return cannot pull more than is available to it (or at least that's what I think he was trying to say)

(b) the white/pink stains are calcium buildup that can be cleaned off

Perhaps it is related to the basement drying out with the installation of the HRV?
The supply and return should match each other. If the return is greater than the supply then it could pull a small negative pressure. This could be bad if the furnace and water heater are in the basement, it could pull fumes from the stack. Later Paul


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Old 11-04-2010, 03:25 PM  
kok328
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I'm thinking this supply should have came from outdoor air to provide pressure balancing and combustion makeup air.

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Old 11-04-2010, 08:05 PM  
paul52446m
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I think right now he is only talking about the hot air and return air for the furnace. But you bring up a good point. As he remodel he needs to make sure that there is enough makeup burner air for things like furnace, water heater,
and dryers, a lot of people forget about this as they box things in. In all new homes it is required to bring at least a 4' duct from out side and tie it into the return air plenum. This will help take care of bath fan and kit, fans taking air out. Later Paul

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