HVAC - Fresh air supply?

[DanCostello]

I just had in the first of a few HVAC guys to talk about upgrading my existing HVAC system to handle my basement-studio-to-be. I live in a 2-story rowhouse that has forced-air ducted a/c covering the first and second floors. A number of threads on here emphasize the importance of removing stale air from a room and replacing it with fresh air. It's for this reason that I had intended to have the basement studio covered by a 2nd zone added to my existing ducted a/c.

However, the a/c guy who just visited gave me a number of reasons why that would be a bad idea. For one, the existing compressor, ductwork, and other equipment isn't designed to handle two zones, so it would be tricky (and quite a bit more expensive) to configure an upgrade like this in a way that wouldn't negatively impact the 1st and 2nd floors.

That part didn't really surprise me.

What did surprise me was when he pointed out that a typical residential a/c unit doesn't provide fresh air anyways - it just cools and recirculates the old air, exactly like a mini-split (which is what he recommended).

So, what then do I do about stale air? Should I look at something like an HRV/ERV or other standalone ventilation system to use in combination with the mini-split?

I seem to recall reading somewhere that it's a code violation to vent from one room into the next, but I can't seem to find that now, though I do see a bunch of home-theater guys talking about installing "dead vents" that do exactly that.

-Dan.

[DanCostello]

Hmm... Upon re-reading the IRC, it looks like I am allowed to use other parts of the house to supply the fresh air, and that, since it's not a bathroom, I could dump the exhaust air into an unfinished part of the basement....

https://codes.iccsafe.org/public/docume ... 53/9853026
https://codes.iccsafe.org/public/docume ... 53/9853329

I may still dump the exhaust outside, but if I can grab the supply air from the living room or entryway on the first floor, that would make certain things easier.

[Soundman2020]

it looks like I am allowed to use other parts of the house to supply the fresh air,

I don't see where you found that in the articles you linked to. Can you be more specific? Quote the actual text and paragraph number.


- Stuart -

[DanCostello]

it looks like I am allowed to use other parts of the house to supply the fresh air,

I don't see where you found that in the articles you linked to. Can you be more specific? Quote the actual text and paragraph number.
- Stuart -

Yep:

Part II - Definitions
Return air - Air removed from an approved conditioned space or location and recirculated or exhausted.

M1507.2 - Recirculation of air
Exhaust air from bathrooms and toilet rooms shall not be recirculated within a residence or to another dwelling unit and shall be exhausted directly to the outdoors. Exhaust air from bathrooms and toilet rooms shall not discharge into an attic, crawl space, or other areas inside the building.

M1602.2 - Return air openings
Return air openings for heating, ventilation, and air conditioning shall comply with all of the following:
<snip>
4.) Return air shall not be taken from a closet, bathroom, toilet room, kitchen, garage, mechanical room, boiler room, furnace room, or unconditioned attic.

Recirculation (which is what I'm talking about) is barely even addressed in the code and, as far as I can tell, generally permitted, with exceptions/restrictions placed on bathrooms, kitchens, and utility rooms. I would be pulling from one conditioned space (1st floor living area) into another conditioned space (basement studio) and then out to either an unconditioned space or outside.

-Dan.

[DanCostello]

Sections 402 & 403 of the International Mechanical Code seem to say the same thing: that recirculation is fine aside from places like kitchens, bathrooms, and utility rooms.

https://codes.iccsafe.org/public/docume ... 49/9788118

(I'd copy/paste the text, but the site won't let me)

[DanCostello]

I think I found a better solution, so I'm scratching this thread and consolidating this discussion back into my main design thread:
http://www.johnlsayers.com/phpBB2/viewt ... es#p141118