HVAC Question: Pushing exhaust air into cold air return?

Hello!

I have built an 8'x8'x9' room in my open basement with 8 plants in a 4x8 chunk of it.

The room has a passive intake at the floor drawing in cold air from the concrete floor (18c to 19c), and exhausting it into my furnace area through a straight piece of 6" rigid ducting between the joists.

I run a 60 pint dehumidifier in the basement so that the air being drawn into the room is already at a low RH without me needing to run dehumidifer inside the room. Essentially my basement is my lung room. The environment is about 1 degree too warm, and the dehumidifer is working hard on it's own.

My basement does not have a cold air return. The warm moist air is just being recirculated in the basement and the dehumidifier is doing most of the work. I'd like to try get my central air more involved, and was wondering if I could take the exhaust from my room and run it into the return of my furnace so it passes over the a/c coil and then gets dehumidified, cooled, and spread around the house (smell is not an issue). Theoretically this should push more air from the basement upstairs causing more warm air to circulate near the thermostat and forcing the a/c to run more consistently. The cold/dehumidified air should then pool back into my basement to be sucked through my room again.

For consideration, if it matters, my furnace is electric, and my house has no gas burning appliances. I do not vent anything outside, but do run an HRV for fresh air periodically.

Is my thinking on the right track? I am sure there is something wrong with this plan, there's always a catch!

Yes you can do it.
I don't have any issues. Just watch out for smells. You kinda get "nose blind" to it after a while.

Can see routing here a bit...

Thanks for replying @.Smoke

I actually lucked out and found a near by spot where Thermopan was used between joists. I found a stick on 6" take-off at Home Depot, cut a hole in the Thermopan and stuck the take-off on. I can hear a bit more air noise upstairs through the returns, but that quickly blends into the background.

Seems to be working and as a possible side effect, it seems like my inline fan isn't working as hard. Likely because it is being assisted by the negative pressure from the cold air return and isn't having to push as hard.

I spent ten years working on HVAC in a complex and I really liked being sent on a call and the problem was resolved by the time I got there. Glad it worked out for you.

printer said:

I spent ten years working on HVAC in a complex and I really liked being sent on a call and the problem was resolved by the time I got there. Glad it worked out for you.

Click to expand...

In your experience, would you approve of this setup as well?

Any warnings or things to watch for? I opted to cut in through the thermopan as it seemed easiest to fix (remove take off, cut new Thermopan to fit, and cover.

I should also mention, I put my exhaust on full speed, and then tested all the upstairs returns with a lighter to make sure they were still pulling. It seems I still have air being pulled into all the returns, so I don't think I've created any large amount of back pressure. I am also pushing the air into the return within 5' of the furnace blower (which is always running for air circulation).

Thanks!

You seem to get the mechanics of it fine. Oh I wish I had your free space.