# Unfinished Basement - Supply vs. Return



## willi5 (Nov 3, 2010)

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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## paul52446m (Nov 3, 2010)

willi5 said:


> 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.
> 
> ...


 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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## kok328 (Nov 4, 2010)

I'm thinking this supply should have came from outdoor air to provide pressure balancing and combustion makeup air.


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## paul52446m (Nov 4, 2010)

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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