I’d like to build a ducting system to actively push air from one room to another. Is that a thing?

So my home office is in our basement while my wife’s is in a finished attic space. We have a mini split system, but it has to be all heat or all cooling, and many days it’s cold in my office, but hot in my wife’s office.

Thanks to a defunct chimney, I have a pretty decent path from the attic to the basement that could easily accommodate some kind of ducting.

I’d like to make a system that can push air from my office to hers or vice versa as needed. I think this would really help the house in general as cold air tends to pool in the basement.

I’ve seen plenty of ducting booster fans, but I’d like something with a speed (or at least direction) control accessible from the outside.

Does something like this exist? It would need to force air through maybe 30-40’ of ducting.

Death_Equity,

Depending on the size of the flue, it would be entirely possible to put a 4"-6" stainless corrugated liner in there with a “T-Body” and “snout” going through the side of the chimney in the attic and close off the damper with an opening for airflow. Then you would have in-line duct fans with a rheostat control at both ends pushing air one way or the other. The duct fans that are the same diameter as the duct don’t have much pressure, so you would probably want a centrifugal fan to spend once and get desired results. You can buy the fan with the speed controller or they do have ones you plug into. The fans are loud, so the Mrs would appreciate it if it were inside of a baffle box to keep the noise down while she works. How low speed the fans can go is limited, so don’t expect to have infinitely varial speeds without spending a lot more.

There also are temperature controllers so you can have the fans cycle to regulate temperature without manual control. You would probably want to put that on only the attic fan if you went that route.

You could use galvanized duct, but it will rot out over time in the flue and it is harder to install vs a stainless corrugated liner.

The fans are $200-400 depending on how much chooch you want. The liner runs $12-16 per foot. The T-Body and snout are about $150-200.

There are bi-directional varial speed duct fans but they carry a premium, typically require custom duct manifold/plenum fabrication, and are two fans put together to achieve the pressure required. Going with one fan at each end is easier, cheaper, and easier to repair should one fan fail.

If it were my project, I would try just having the fan in the attic pulling and control it with a speed control plus temperature controller. If that wasn’t enough is when I would add the fan in the basement and do manual control with variable speed and have both fans push. I don’t really see why you would want to pull air from the attic, but you seem to feel you would need to.

It can be tricky to get the snout on the T-Body, you will want some 1/4" extensions and impact, as well as someone who can help you.

Bizarroland,
Bizarroland avatar

I've been thinking about building a similar system for my home.

I live in a geodesic home and the main floor is almost always at a comfortable temperature but the basement floor is always cold.

Thinking about purchasing some vent booster registers and wiring them in with some ducting in one of the walls to suck the cold air out of the basement and push it up into the main floor or possibly all the way up to the top floor.

I checked AliExpress and there were some sellers there who had what I was looking for in the 40 to $80 range, but I imagine the main cost is going to be dropping 10 to 20 ft of ducting through the walls.

I don't think that one of them by itself will completely solve the problem but I feel like since it would be sucking the coldest air in the entire house and mixing it in with the hottest air in the entire house that it would at least help ameliorate the issues.

Death_Equity,

In your case there are a lot of complexities that may make such a simple solution less viable than OPs.

The total volume of the two spaces, the floor and wall construction, if the basement is finished, and the layout of the basement and main floor all come into play.

Adding ducting to the walls may be a major hassle and expense.

If it were my house, I would probably push air up from two spots into the main floor via registers I added or add more returns to the basement and hope the HVAC circulation helps with the top floor without having to add dampers to the main and top floors in both cases.

Bizarroland,
Bizarroland avatar

I tested the idea with a small blower fan. Well I say small but it's a decent sized and can move a lot of air.

I put it at the base of the stairs and by itself it caused the air temperatures to normalize between the bottom floor and the middle floor.

But it's also super power hungry and I don't want to burn 300 watts of power an hour 24/7 to normalize the Air temps.

There is a central wall that goes from the top to the bottom in the middle of the dome and I believe there is a pocket that I can utilize to hide the ducting.

I guess when I finally execute on the plan I'll take some pictures and show off my handiwork.

ch00f,

Should have been more precise. I have a funny situation. My house has had four major remodels performed over the past 80 years. One of them involved extending the roof and totally covering a chimney (there is another chimney elsewhere in the house). Rather than remove the chimney, they built around it including adding a closet on the middle floor. The closet is wider than the chimney, but the whole thing is framed out as a rectangle, so I have like 1x2’ of empty space leading from my attic to the basement ceiling.

So not need for liners.

I don’t really see why you would want to pull air from the attic, but you seem to feel you would need to.

I’m by no means an HVAC expert, but I was thinking that pulling hot air from the hottest point in the house (attic room ceiling) would provide the best circulation. Thinking more about it, I think I’d be better off having it be one-directional if only so I can install a filter to keep it from filling up with dust. I can convince myself that either direction is the better option. Maybe I’ll install the blower somewhere in the middle where it’s easy to access.

Thanks for the advice!

Death_Equity,

If the masonry is gone and there is just a framed out hole then galvanized would totally work with fairly easy install with the help of a second person or some clever use of support. You wouldn’t want to just blow air through the cavity without ducting as it would be horribly inefficient and tank the air velocity across that much distance.

Adding an in-line towards the middle does mean having controls up in the attic more involved and you do want the Mrs to have control over the fan there instead of her having to go downstairs.

If you wanted to circulate the air instead of forcing air with a passive return, then you get into a more complex situation with two ducts and fairly informed placement of intake and return.

Pulling into the attic will help to lower temps and will be the simplest/cheapest option so long as there isn’t a wall you can put a window heat pump unit in.

ch00f,

Do you think I could get away with some flexible ducting? Might be hard to navigate the rigid stuff into these spaces. Also, insulated ducting or no (thinking about condensation).

Death_Equity,

When you say flexible ducting, are you talking aluminized plastic or the corrugated aluminum? That would be a fair amount of weight for flexi in either case, you would want to have access along the route to secure it, especially if it is insulated. The aluminized plastic would need more support than aluminum.

Without site inspection, I couldn’t say how necessary insulating the duct would be. Using insulated duct would be a good “better safe than sorry” move but will make installation without full access a bit of a bother.

intensely_human,

I mean what else are ducts for?

meathorse,

Heat transfer kits - some have thermostats that can control the flow else flick them on manually:

www.mitre10.co.nz/shop/heating-cooling/…/RS2063?i…

ch00f,

Oh neat! I knew I couldn’t be the only one.

victorz,

This is what the Internet was made for. People helping people.

Love you guys. ❤️

Wrench,

That’s a pretty elaborate plan to crop dust your wife from two floors away. Respect.

Knossos,

Thank you for the chuckle.

Tull_Pantera,

Yes. The unit and controls can be at the entrance from the rooms into the chimney, and you’ll need to cover the top of the chimney to get flow from room to room, and put air filters in-between the fans and the chimney if it has ever been used. If you want to get a little fancier, you can have the top of the chimney open and close so that you can pull air from outside or vent air out of both areas…

reddfugee,

I have wondered the same thing, the front of my house (where the living room and gaming PC are) gets a lot of sun so it is always a few degrees warmer than the back bedroom. My wife would rather melt than put a hole in the ceiling so I have not been allowed to try to fix it lol.

zcd,

You could set up a range hood In the old fireplace/chimney to push air upstairs, they usually have a few speed settings. Or you could use an inline fan duct plugged into a variable speed controller. If you go big (500 cfm+? Depends on where you are) you may need to consider adding makeup air as well

deegeese,

If there’s no exhaust to outside, there is no air lost to makeup.

Proper functioning of the duct will require the source and destination rooms leave a door open to the rest of the house.

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