Abandoned Chimney Usable for AC Ducts?

jp_2

Ok, but what happens when the next owner decides hes going to use the chimney for a chimney?

D107

I've seen chimneys used for laundry exhausts, etc.

I was thinking that if I went mod-con on my next boiler,I could use the abandoned 1924 terra-cotta-lined chimney for the main and second floor AC ducts and get rid of the big 8" ducts now going through my closets. Currently have a 3 ton Bryant from 1992. Would also hope to hook up an HRV (or ERV?) to system.

Chimney's inside measurement is 7x11, adjacent to a fireplace flu of same size. If so, would I need an overall liner in which to put the ducts? Hate to waste all that space.

Thanks,

David

Brad White_9

That would be duct up...

Hi David-

A duct of that size and allowing for the neat rounded corners is roughly equivalent to a 9 inch diameter duct.

(OK, you ask, "Brad, what does that mean?" )

That duct will pass about 300 cfm, more than a metric squirrel fart, less than most systems can deliver.
About enough for about 3/4 of a ton of AC. May do a small to medium size room depending on exposure.

Personally, I would not use it at all for I cannot determine how well it is sealed nor how clean it is. Plus it is not insulated. Condensation can occur at some point. I might consider it for return air provided I have very good filters before I recirculate. But the proximity to combustion in adjacent flues? I could not recommend it for others. Probably would not do it in my own house.

If you could drop in a liner, the size reduction would not allow it to be worth the effort, IMHO.

Instead I would use it to hide the family silver, your Krugerrands and Marvel Comics collection. And do not tell a soul!

Brad

D107

good points both

Seems that the adjacent fireplace flue would be the most problematic--maybe even against code. As for size, I had thought the unico ducts were very very small and would fit within a metal liner.

As for return to chimney use, one would hope that if I installed a mod-con an eventual buyer of my house wouldn't go back to natural draft, but it's certainly a possibility. The wallies seem split as to viability of direct venting.

Thanks,

David

Paul Aguilar

UNICO ducts and your current Bryant system are not compatible. You may want to consider changing the round risers through you closet into a flatter rectagular in order to gain space. Using the chimney most likely would not give you the results you need for the effort involved. And yes, it should be a class 1 duct (proper liner with insulation) which means very little air flow after taking into consideration the 7" starting width.

Tombig_2

Chimney chase

One of the harder things to do in a retrofit AC only Unico installation is get a decent high return at the second floor from basement equipment. You could probably oval some 8" and push it down the chase. 9" might be pushing your luck. Since it's a return you wouldn't necessarily have to insulate it. I would use 26 guage and seal all joints. Don't even consider without a liner. BTW..7x11 would make a nice chase for two 3" PVC's for your condensing boiler. Your Bryant condenser is compatible with Unico but you must use their air handler and their duct system design.

D107

ac is in attic

but good ideas. I had heard you could exhaust and intake via chimney for a mod con. One advantage might be to warm the incoming air without having to put a vaccuum relief valve in the boiler room. Hopefully I wouldn't need a liner around those two 3" pvcs. Of course this might cost me more than going through my foundation wall and I think I'd have to insulate the exhaust line to prevent condensation yes?

Thanks,

David

Tombig_2

PVC exhaust

> but good ideas. I had heard you could exhaust and

> intake via chimney for a mod con. One advantage

> might be to warm the incoming air without having

> to put a vaccuum relief valve in the boiler room.

> Hopefully I wouldn't need a liner around those

> two 3" pvcs. Of course this might cost me more

> than going through my foundation wall and I think

> I'd have to insulate the exhaust line to prevent

> condensation yes?

>

> Thanks,

>

> David

Tombig_2

PVC exhaust

David, most of my installs are urban and sidewall venting is always an issue due due adjacent building openings. I always look for a way to vent to the roof. All manufacturers recommend insulating the exhaust through unheated space. The intake doesn't need to be insulated.

If you converted your entire duct supply system to high velocity (the returns could be reused) you could use that as a chase for maybe 6-9 branch runs. The two inch supply tube is already insulated but watch out for the length of the runs. Probably tear up some foil scrim pulling them down the clay liner. Delivery CFM starts to derate after 25' of branch run. By the time you ran 20' down the chase and horizontally through the basement to your floor terminations you might be at 50-60% reduction, meaning you would need twice as many branches to get needed delivery. Do your unico homework. Good Luck