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Vertical chases


rockford33's Avatar
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Join Date: Aug 2003
Posts: 239
MD

07-09-10, 03:46 PM   #1  
Vertical chases

Quote:
Originally Posted by rockford33
Bud,
I was reading through the forums and saw a post by you recommending to seal up a vertical cavity, particularly if it went from the basement to the attic.

I have a 4 story townhouse and I believe I have located the HVAC duct chase that goes from the 1st floor to the 4th floor for the ducting and return air vents. Would it be a good idea to seal this chase at the 1st floor ceiling (if I can get to it, it is in the back of the HVAC closet). I have not looked to see if it is already sealed, but my 1st floor is always cold (nice right now with the heat wave though ), and the 4th floor is hot. Since the HVAC closet just has louvered bi-fold doors, the chase is open to the conditioned space.

Just wondering if I am getting an unintended chimney effect with hot air from the 1st floor (with HVAC vents in the ceiling) to the 4th floor (no attic, but tray ceiling and dormers). Winter time is awful on teh 1st floor with it dipping down to 60 degrees (with t-stat set to 68, and 4th floor will get into the 70's easily).

Thanks,
Neil
Hi Neil,
All buildings experience an increased pressure on the upper floors and decreased on lower floors due to that hot air rising as you mentioned. The higher the building and the better the connection between the floors, the higher the pressure, so an open chase way should be closed off as much as possible. A simple smoke test will show you what is happening. These pressure levels are very small, but are there 24/7 so do affect the building heat loss.

The other area that can add to your problems is the normal leakage from all of those ducts. Four floors is a long way to push and pull warm and cold air. The normal seams need to be super sealed. That may not be practical, but seal as much as you can reach. Foil tape or duct mastic.

If these ducts are used for heating and ac, then the balance between seasons is very difficult. Having extra capacity high and low would allow some registers to be closed where the particular conditioned air is not needed for that season. ie, less heat upstairs and more downstairs in winter. But after each seasonal switch, the system wants to experience the correct amount of air flow, so it's not just a case of opening and closing randomly.

Space gets limited using the PM so if you have more questions, just repost on the forum and I will pick it up. The management of this forum prefers that everything be shared with the public as many people just read and never post. Your question can end up helping many other people.

Use the PM when I'm asleep and miss your post .

Glad to help, and there are more steps I can cover about simple improvements that can improve comfort and reduce costs.

Bud

 
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rockford33's Avatar
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Join Date: Aug 2003
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07-09-10, 03:55 PM   #2  
Bud,
Thanks for the reply. I hope you don't mind, but I posted the question and your answer in a new thread for all to see.

I do have some more to add based on your reply. As far as I know (from looking into the vents), all of the ductwork is the flexible kind, and inaccessible since all areas are finished with drywall. The only area I can get to is the front and a portion of the side of the air handler/furnace, where I did use foil tape to seal all the leaks/seams.

From a recent AC inspection, the tech told me the AC unit and furnace appeared a little undersized. I suspect the duct work and return are as well, and as you noted, 4 stories is a long way to be pushing and pulling air. Is there any way to improve that? I have thought of duct boosters, but as I noted, the duct work is inaccessible (and would they work in flexible ducting?), so don't think that idea will work.

Hopefully if I can get to the vertical chase and seal it at the first floor, it might a small but noticeable difference. I will have to try the smoke test and see what happens. I also have some air sealing to do around the house (HUGE leak at my 1st floor direct vent fireplace), but finishing other projects has taken priority (wife doesn't take kindly to multiple holes in the drywall for the past few months ).

I plan on getting a home energy audit sometime this summer, so hopefully that will point out some of the less obvious/easily visible places that energy is leaking. Having a 10-15 degree difference from the bottom floor to the top floor is not ideal, but there may not be much I can do with the existing system and layout without a lot of expense.

Thanks,
Neil

 
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