Cold Basement. (6-8'c difference with main and 2nd floor)

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Jun 26th, 2022 8:06 pm

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Jun 25th, 2022 11:46 am

blackn54 [OP]: Member; Sep 19, 2014; 488 posts; 254 upvotes; Markham, ON

Jun 25th, 2022 11:46 am

Cold Basement. (6-8'c difference with main and 2nd floor)

We had our basement finished last year.

Before the basement were finished, the temp is usually around 20'C. (The main floor is always set to 23'C year round)

But now, when the main floor is at 23'C, the basement is constantly at 16'C.
This is the same during winter when it is -20'C outside, or summer like now when it is 30+'C outside. (So I dont' think it is due to insufficient insulation)

I know cold air sink and hot air raise, but 6'C difference seems like a lot...also why would the difference became so much more after the basement is finished?

I tried shutting off all the vents now since it is blowing cold air now (The shut off is not air tight), but temp is still hovering around 16'C...

Any idea why that is and how I can minimize the temp difference?

17 replies

Jun 25th, 2022 12:13 pm

tew: Deal Fanatic; Jun 13, 2010; 5407 posts; 6494 upvotes; GTA

Jun 25th, 2022 12:13 pm

Since you insulated your cold conditioned air is staying in your house (basement) and not leaking out anywhere near as much. So your basement will be colder in the summer with the AC running than it was before. To minimize the temp difference run the furnace fan 24/7 to circulate the air in the house.

Last edited by tew on Jun 25th, 2022 12:18 pm, edited 1 time in total.

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Jun 25th, 2022 12:17 pm

IndyBeak: Deal Addict; Sep 13, 2016; 3376 posts; 2121 upvotes; Mississauga

Jun 25th, 2022 12:17 pm

You can only do so much. Basement will always be the coldest floor. And a diff of 7-8 degrees is not out of ordinary.

This is what my sensors are reporting at the moment.

See how basement is a good 10 degrees lesser than a bedroom upstairs which is in front of the house and gets a lot of direct sunlight for most part of the day.

Screenshot_20220625-121516_Home Assistant.jpg

+1

Jun 25th, 2022 12:31 pm

pootza: Deal Addict; Dec 19, 2009; 4846 posts; 2770 upvotes

Jun 25th, 2022 12:31 pm

Basements will tend to be cooler than the main/2nd floors because they do not gain as much heat from the hot summer temperatures outside because most of the basement is BELOW GROUND where the ground is cooler than the air.

Jun 25th, 2022 12:41 pm

blackn54 [OP]: Member; Sep 19, 2014; 488 posts; 254 upvotes; Markham, ON

Jun 25th, 2022 12:41 pm

I just thought the difference is a bit much (6'C with main and 7-8'C with 2nd Floor)
And the difference wasn't that much before the basement was finished. (3-4'C difference)

tbh 16'C makes the basement almost unusable...

Jun 25th, 2022 12:46 pm

vrscdx: Sr. Member; Jun 23, 2019; 501 posts; 330 upvotes

Jun 25th, 2022 12:46 pm

Also in the summer keep the door to the basement closed so the A/C air from the main floor doesn't go down into the basement.

+2

Jun 25th, 2022 2:55 pm

mrweather: Deal Fanatic; Aug 29, 2011; 7986 posts; 4929 upvotes; Mississauga

Jun 25th, 2022 2:55 pm

Try running the furnace fan continuously so that air gets circulated all the time throughout the house. I do that and combined with closing off the vents to our finished basement, I see at most a 2-3C temperature difference between the floors.

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Jun 25th, 2022 3:00 pm

teoconca: Deal Fanatic; Oct 16, 2008; 9602 posts; 3930 upvotes

Jun 25th, 2022 3:00 pm

^^^ Try that ^^^ also close door to basement in summer. Open in winter.

...

Jun 25th, 2022 3:05 pm

quick90: Member; Jun 2, 2007; 439 posts; 80 upvotes; Toronto

Jun 25th, 2022 3:05 pm

I agree with the comment to keep your furnace fan running 24/7.

Some furnaces allow you to adjust the air flow CFM for the "fan only" mode. If you dig into the manual you might be able to increase the rate, which would further help.

+2

Jun 25th, 2022 3:25 pm

cheapmeister: Deal Guru; Feb 23, 2008; 12571 posts; 1467 upvotes; Brampton

Jun 25th, 2022 3:25 pm

Run a dehumidifier to remove the dampness which does make it feel colder.
Also open basement windows to let in the warm outside air.

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Jun 25th, 2022 3:56 pm

CaptSmethwick: Deal Fanatic; Oct 12, 2007; 7423 posts; 5423 upvotes; Ottawa

Jun 25th, 2022 3:56 pm

As above posters have said: keep the furnace fan running continuously. As another said, use a dehumidifier (or two). Also, make sure your cold air returns in the basement are open and check for the duct dampers - you want the air to have less restrictions against climbing to the upper stories. Finally, don't use a filter above MERV8 (MERV 6 is better in the summer in my experience) and keep it clean.

Jun 25th, 2022 10:13 pm

dling7: Deal Addict; Apr 3, 2006; 1241 posts; 465 upvotes

Jun 25th, 2022 10:13 pm

When having your basement finished perhaps they closed or blocked the cold air return. You need at least one in the basement with 6” duct to pull the cold damp air and will also more easily cool your house.

If your basement was finished properly with Vapor barrier on floor and walls you shouldn’t need a dehumidifier, from my understanding. Make sure your floor vents on top floor are all open in the summer, so not to keep air being kept in basement.

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Jun 25th, 2022 10:16 pm

engineered: Deal Expert; Feb 11, 2007; 18977 posts; 21792 upvotes; GTA

Jun 25th, 2022 10:16 pm

tew wrote: ↑Since you insulated your cold conditioned air is staying in your house (basement) and not leaking out anywhere near as much. So your basement will be colder in the summer with the AC running than it was before. To minimize the temp difference run the furnace fan 24/7 to circulate the air in the house.

blackn54 wrote: ↑I just thought the difference is a bit much (6'C with main and 7-8'C with 2nd Floor)
And the difference wasn't that much before the basement was finished. (3-4'C difference)
tbh 16'C makes the basement almost unusable...

See above ^^^
Also, put some tape over your basement vents to seal them up, or shove a bag behind the vent.
Also be sure to open any return vents there, and if there aren't, you can just open up a return access panel, or your humidifier, which will suck in cold air and blow it upstairs.
Also seal any leaks in your duct work in the basement with foil tape or mastic paste.

mrweather wrote: ↑ Try running the furnace fan continuously so that air gets circulated all the time throughout the house. I do that and combined with closing off the vents to our finished basement, I see at most a 2-3C temperature difference between the floors.

+1

I do all of the above and my basement is still 5-8'C colder than the 2nd floor.

If the women don't find you handsome, they should at least find you handy.

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Jun 25th, 2022 11:54 pm

jrbb0309: Sr. Member; Jan 8, 2009; 868 posts; 555 upvotes; Simcoe County

Jun 25th, 2022 11:54 pm

What's the humidity level in the basement? Ours (finished) was that much of a difference until we checked the humidity (using a hygrometer) and started using a dehumidifier. Now it's a lot more bearable in the summer.

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Jun 26th, 2022 7:19 am

mrweather: Deal Fanatic; Aug 29, 2011; 7986 posts; 4929 upvotes; Mississauga

Jun 26th, 2022 7:19 am

engineered wrote: ↑ I do all of the above and my basement is still 5-8'C colder than the 2nd floor.

Not sure what else to suggest. Maybe you have a lot of leakage in the existing ductwork? Apparently, somthing like up to 20% air loss due to leaks is acceptable. Before we finished our basement, I sealed every connection I could find with foil tape.

Right now, the basement is 22, the main floor is 24 and the second floor is 25.

Jun 26th, 2022 2:24 pm

jdmfishingonly: Deal Fanatic; Oct 13, 2008; 5936 posts; 2676 upvotes; Durham

Jun 26th, 2022 2:24 pm

Well ... I just checked the Temps. All normal to me. And I work in the basement (home office in the basement).

Second Floor Bedroom ... south facing at the front of the house above the garage ... 25 degrees

Main Floor Dining/Living Room ... middle of the house ... 23.5 degrees

Basement ... unfinished ... 18 degrees

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Jun 26th, 2022 3:55 pm

engineered: Deal Expert; Feb 11, 2007; 18977 posts; 21792 upvotes; GTA

Jun 26th, 2022 3:55 pm

mrweather wrote: ↑ Not sure what else to suggest. Maybe you have a lot of leakage in the existing ductwork? Apparently, somthing like up to 20% air loss due to leaks is acceptable. Before we finished our basement, I sealed every connection I could find with foil tape.

Right now, the basement is 22, the main floor is 24 and the second floor is 25.

Mine's also a 5 level split, so I think the temperature difference is exaggerated.

If the women don't find you handsome, they should at least find you handy.

Jun 26th, 2022 8:06 pm

rdx: Deal Fanatic; Jun 7, 2005; 9579 posts; 1045 upvotes

Jun 26th, 2022 8:06 pm

Close all vents in the basement.

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