# Not exactly another room to room heat transfer question

| Posted in General Questions on

I’m familiar enough with the physics of heat transfer to understand the inneficiency behind trying to move 72 degree air into a 65 degree room in an effort to make it warmer.

But.  I’m finding less information on the opposite problem.  My mini split system keeps the whole home toasty warm in the winter, but in the summer the second level is conditioned by a single head and the bedroom is too warm.  Would I encounter the same problems in trying to remove hot air near the ceiling and pushing that air down to the first level where I could refrigerate Coke on the counter if I wanted?

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### Replies

1. | | #1

Yes, moving hot air from the second floor down to a cooler first floor is virtually impossible.

1. | | #2

I’m assuming attempting to blow cold air up from the first level wouldn’t be any easier? Haha...

1. | | #4

Not sure which way would be easier, but either way is difficult enough to be impractical. The ERV method won't work either, just not enough heat difference in the volume of air that an ERV moves. It's not really convective flow you're fighting, it's the natural stratification of the air.

1. | | #5

Good deal. I figured if it was easy then it would be easy to find someone that’s done it. But also not wanting to buy an additional unit for 4 degrees 3 months out of the year.

2. | | #3

I’ve even considered tweaking the ERV so that I’m exhausting more air from the first level in an attempt to battle the convective flow, but I’m assuming pretty much anything short of adding a second mini split is going to be fruitless.

It’s not terrible, probably 76 degrees on the hottest days - and Is prefer more like 72.

3. | | #6

In the case where you can install a ceiling fan than moves air from the ceiling of the second floor to the first floor, a useful amount of "thermal destratification" is easy.

1. | | #7

This is so simple, and yet I didn’t think about it. I have a big stairwell with a chandelier that could easily be replaced with a nice looking, powerful fan.

Thank you!

1. | | #8

Let us know how it works. I tried the same thing, but with an 800cfm blower in the stairwell. Didn't do a thing. It seems to me that if anything, higher velocity directed air would have a greater effect than a ceiling fan, but maybe my intuition is wrong.

1. | | #9

Will do. I found a beautiful 72” 2000 cfm fan, that even worst case scenario will look amazing in the space I’m planning to use it.

I’m also adding a low profile ceiling fan in the bedroom itself and a transfer grill. I have a thermometer/humidistat in every room, and a energy monitor on every circuit - so the results reported will not be guesswork!

1. | | #11

This shows a ceiling fan working very well, even in Winter (when you need to avoid drafts). But not clear to me just how low one can go with cfm and velocity (which determines throw). Without more research, I'd be tempted to get a multi-speed fan that has an option to go higher (perhaps to > 6000 cfm).

https://dash.harvard.edu/bitstream/handle/1/29312101/Residential_Fans-Destratification.pdf?sequence=1

2. Expert Member
| | #10

Sometimes you actually want a large, slow moving, volume of air for this application and not the small, directed flow you get with a high velocity blower. The high velocity flow usually results in very localized changes.

Ceiling fans work well in this application, especially in large open areas. The more confined the air path to the lower level is, the less effective the ceiling fan will be.

Bill

4. Expert Member
| | #12

The ceiling fan can work well in a large open space where the bedrooms are in a loft type of place. I have this at the cottage and the main floor wall mount + ceiling fan works for cooling upstairs.

In a typical house without a large void between the first and 2nd floor, I don't think you can get enough mixing.

By the time you get a fan with high enough CFM at low enough velocity not to be annoying and somehow distribute that airflow to the rooms, you are spending as much money as a budget mini split AC unit. I would just bite the bullet and install a 2nd unit upstairs.

Something like this could work well:
https://ashp.neep.org/#!/product/29606

The nice part about these units is that you can connect up ducts to it (square cutouts on the side) and T off some of the airflow. It is not really meant to be used for feeding individual rooms, but if you size things correctly with a large transfer duct, it should work.

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