ColinC
New Member
Posts:27
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| 22 Nov 2015 01:21 PM |
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Hello,
I have a 1970s open floorplan home with 3 levels (basement, main, 2nd floor), with an open 8’ x 8’ staircase connecting all three levels. All 3 levels have relatively low ceilings (about 7.5’). Although there is electric baseboard heat throughout the house, I’m trying to reduce that with a woodburning stove and heat coming in from an attached sunspace. Both of these heat sources are on the main level, and the heat moves across the low ceiling until it hits that open staircase and then up like a chimney onto the 2nd floor. Some of that is just fine, but since the 2nd floor is used mainly for sleeping, I’d like to keep more of that warm air on the main level. Also, since the staircase is in the middle of the main floor, heat from the stove on one end often doesn’t it “make” it to the opposite end before being pulled up onto the 2nd floor, and vice-versa with heat coming in from the attached sunspace on the other end.
There’s not much I want to do at this point with altering the basic floorplan, but one thing I want to try is installing a ceiling fan from the ceiling of the 8’ x 8’ staircase to see if I couldn’t “push” some of that hot air back down to stay on that main level.
My main question is would it be best to install the ceiling fan fairly close to the ceiling, or drop it down with a downrod maybe 2-3 feet? It’s a little hard to see from the pictures, but the distance between the ceiling of the staircase from which the fan would be dropped and the ceiling of the main level is about 8.5’, and then another 7.5’ to the floor of the main level.
Another issue is fan direction. I’ve read conflicting advice about whether you run the fan in a reverse (air being pulled “up” towards the ceiling) in winter for recirculating warm air. But what I’m trying to do here may not call for the same solution. And whether I run the fan “down” or “up” may impact whether it makes sense to mount it close to the ceiling or drop it a few feet.
Thoughts? Thanks for your time,
Colin
Picture 1
Picture 2
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chrs
Basic Member
Posts:136
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| 22 Nov 2015 02:52 PM |
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1) Before anything else, do a good job of air sealing in the attic. A lot of the airflow is in the basement, up the stairs, and out the attic, and that airflow carries the heat with it. If the air can't flow out the attic, it won't go up the stairs either. Top priority is the attic, second the basement.
2) The fan primarily increases air circulation. That won't help unless the upstairs is actually hotter than the downstairs.
3) The main reason a fan direction matters is that it changes how much the air hits the humans below it. It the summer, that helps cool the humans, so blowing down is good. In the winter you don't want that effect. But in your case, I don't think that matters much because humans don't hang out in the stairwell much.
4) It's possible you could reduce the air leakage out the attic a tiny bit by having the fan blow downward, thereby slightly depressurizing the upstairs. But that seems like a poor way to accomplish what you could do better by air sealing the attic. To do that you'd want the fan mounted as low as is feasible. |
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ColinC
New Member
Posts:27
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| 22 Nov 2015 03:32 PM |
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I'm glad you discussed the attic sealing issue, because I wondered about that. My roof has 6 passive/static vents into the attic, as well as two plumbing stacks/vents. By "attic sealing" I assume you mean sealing off any penetrations into the attic from the 2nd floor living space? The two main culprits are a whole-house fan intake and an attic access hatch, both about 3' x 3' ( picture). Additionally, there are some ceiling fixtures (bathroom lights, ceiling fans, etc.) they may not be adequately sealed. But I suspect the main issue would be those two large penetrations very near the top of the stairwell. I'm not sure what good options exist for sealing them more effectively than I have them short of applying some removable sealant/caulk to both. Both have foam & bat insulating "liners" behind them, and this season I applied some of the "shrinkable" window film to the whole house fan louvre to seal that more effectively. But this is what you are talking about in terms of "sealing the attic", or not? Thanks! |
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chrs
Basic Member
Posts:136
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| 22 Nov 2015 03:53 PM |
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Yes, sealing penetrations from the 2nd floor into the attic...and from the wall cavities into the attic.
I like the guide put out by Energy Star for this:
https://www.energystar.gov/ia/partners/publications/pubdocs/DIY_Guide_May_2008.pdf?2e20-e06c
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Bob I
Veteran Member
Posts:1435
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| 22 Nov 2015 05:10 PM |
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A blower door test would tell you if there is air leaking into the attic and if so, where it is leaking, and where it is leaking from. My guess is that on the attic side it's a combination of the attic hatch and the whole house fan since they are typical suspects and can leak a lot of air. When the blower door is going you can look through an infrared camera and see where the cold air is coming in. Reverse the flow of air, turn on a fog machine and you can see the air leaking out of the house - although you;d have to be in the attic to see fog coming in. You would see, for instance, where the air leaks are bringing cold air into the house.
The attic hatch panel - (plywood) should be adhered to 6"+ of foam board for insulation and should be surrounded by a plywood "well" to hold back the attic insulation & tightly surround the panel. The inside lip of the panel should be weatherstripped and have some type of positive closure to pull the panel onto the weatherstripping.
Keep in mind the 2nd law of thermodynamics: "heat flows to cold". It's common knowledge that in many buildings the higher floors are naturally cooler, but
in a well built super insulated house all three floors would have similar temperatures, within a couple of degrees and not too noticeable. This is due to two factors: the house would have no air leaks and all surfaces bordering the exterior (or attic) would be warm. So there would be no cold air on the attic surfaces to be attracting heat, and no air leaks which may be pulling air up into the attic. Since in your house the higher floors are noticeable warmer, one of both of these factors are not working as they should be.
If warm air is moving to the higher floor, it is likely being "pulled" by some force.
Air leaking from the house into the attic is being pulled into the house somewhere - most often it is being pulled into the basement through unsealed rim joists, unsealed basement bullheads. These are fixable.
A good energy auditor can identify the exact places that need work. |
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| Bob Irving<br>RH Irving Homebuilders<br>Certified Passive House Consultant |
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ColinC
New Member
Posts:27
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| 22 Nov 2015 07:10 PM |
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[snip] ... in a well built super insulated house all three floors would have similar temperatures..." Unfortunately that would not be this house  I did go around this afternoon with my highly-scientific incense stick and temp gun to sniff out leaks. It was fairly windy outside, so I was able to determine some penetrations pulling air into the attic on the 2nd floor. Perhaps the main culprit--hiding in plain sight--was a pocket door in the bathroom. The cavity into which the door "stores" does not appear to be insulated/sealed at all, and with gusts of wind it was easy to see the "vacuum" pulling air into that space. We don't use that door so I removed it and sealed it up. So hopefully all that sealing will make a difference. But back to my original question...assuming a ceiling fan in that stairwell might do at least some good, would mounting it closer to that ceiling, or dropped down below it some distance, be the likely best strategy based on what I've described, the dimensions of the stairwell, distance between ceiling/floors/etc.? Thank you, |
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Dana1
Senior Member
Posts:6991
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| 23 Nov 2015 03:04 PM |
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In almost every case, running the ceiling fan fast enough to make a difference in temperature adds enough wind chill that humans are actually LESS comfortable.
If you're trying to satisfy a thermostat blast away with the fan, but if you're trying to satisfy the occupants, don't-apply your efforts elsewhere.
With high intensity heat sources like wood stoves there is a sufficient temperature difference to induce quite a bit of convection & stratification. Air sealing is always a good idea and will help with the overall heating situation, but it won't stop the stratification issue. The 200-300F air rising off the wood stove is far more buoyant than 70F air. A doored-off stair case would allow you to adjust the amount of convection exchange with the upstairs, but it doesn't look like that's a realistic solution for your current layout. |
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ColinC
New Member
Posts:27
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| 23 Nov 2015 06:07 PM |
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None of the occupants spend much time in or immediately near the stairwell where the ceiling fan would be installed, so that really isn't a consideration. My thinking was that since that stairwell is effectively serving as a "chimney" funneling heat up onto the second floor, so that using a fan to try to reverse some of that movement might be beneficial. Not to anyone/anything directly under the fan, but presumably that warmer air being "forced" down would hit other surfaces and recirculate around the living areas.
Remember also that the stove isn't the only heat source. The heat coming from my attached sunspace enters at 95-100deg tops, usually it is in the 70s-80s.
I don't have particularly high expectations for this idea...the stairwell was already wired for a light which it needs...I'm merely installing a fan with that light and was wanting input on the distance-to-ceiling and fan direction issues...
Thanks,
Posted By Dana1 on 23 Nov 2015 03:04 PM
In almost every case, running the ceiling fan fast enough to make a difference in temperature adds enough wind chill that humans are actually LESS comfortable.
If you're trying to satisfy a thermostat blast away with the fan, but if you're trying to satisfy the occupants, don't-apply your efforts elsewhere.
[snip] |
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FBBP
Veteran Member
Posts:1215
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| 23 Nov 2015 06:30 PM |
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Colin - Dana pretty much covers it. Some times it makes it easier to visualize if you consider that the colder denier air actually displaces the warmer air. So in your case the cooler air on both floors want to drop down a level and this pushes the warm air up.
If the house is totally sealed, you would still have the convectional air currents as long as there is cooler air above warmer air. And there almost always is. As the hottest air is pushed against the ceiling, it cools and starts to fall. And as mentioned it will always be worse with a high heat source then with just your baseboard heat.
If you are going to put in the fan (an it won't be all that effective) move it to the back of the stairway so that there is room for the return air in front of it. However chances are that you will just set up an air circuit in the staircase without dramatically effecting the rest of the house. A small squirrel cage blower on the header over the first floor stairs blowing down away from the staircase, will probably do more good but even that is limited.
A ceiling mounted fan above the stove directing the hottest air away from the stair case will probably do more good.
In commercial projects when we have an opening in the floor that separates two floors for fire purposes, we need to install a smoke baffle around the opening. This is usually a drywall wall or bulkhead coming down about 12" from the ceiling. The idea is that the smoke that develops from a main floor fire will hit this bullhead and be force down. As it comes down, it is cooling which starts the convection path back downward, slowing the infiltration of the smoke entering the second floor. You might try something like that to see how it works. Maybe just take a 12 inch strip of poly or cloth and tack it up around the opening.
Another (more expensive) way would be to install a ductwork from the ceiling above the stove location, down into the basement and bring it back up to the main floor at the far end of the house. A small squirrel cage blower in the basement would move the air. |
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jonr
Senior Member
Posts:5341
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| 23 Nov 2015 07:44 PM |
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Should be more efficient to point a fan at the wood stove, pointing away from any people (to minimize drafts). More air moving the same BTU (away from the stove) means a lower air temp. And a lower air temp means weaker convection and less stratification. A little like what a forced air furnace does. Moving lower temp air (ie, post stratification) gets expensive (many more CFM for the same BTU moved).
Your sunspace heat is a lower grade and won't stratify so much.
With electric baseboard heat, I'd be putting some of my effort into air source heat pumps. |
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FBBP
Veteran Member
Posts:1215
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| 23 Nov 2015 09:17 PM |
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The air at the ceiling above the stove should be the hottest air as it rises. Blowing cold air at the stove just breaks up the stratification without directing it anywhere. In this case we would want to blow it away from the staircase. |
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jonr
Senior Member
Posts:5341
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| 23 Nov 2015 09:47 PM |
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The air at the ceiling above the stove should be the hottest air as it rises. The air at the surface of the stove is hundreds of degrees (although not all of this will be transferred). The air at the ceiling is something more like 80F - a diluted, lower temp version of what's coming off the stove. If you want to move heat efficiently, start at the source. Blowing air horizontally across the stove and towards the other side of the house will help with the OP's goal of evenly heating the main level. With less fan power and drafts than moving cooler air. Plus it's 90 degrees vs 180 from the direction the hot air wants to flow (due to convection). If you want to move heat horizontally, don't blow vertically. |
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FBBP
Veteran Member
Posts:1215
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| 24 Nov 2015 09:44 AM |
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The air at the ceiling above a wood stove will be 90º to 110º and maybe much higher. The ceiling MOUNTED fan (not a CEILING fan) would blow horizontally in the direction of the far corner of the room, along the ceiling, accelerating the natural convection flow. The hottest air will be at the ceiling. We want to force it to the far side away from the staircase.
Blowing horizontally across the stove would blow it at the occupant level and create air currents below the hottest air at the ceiling. |
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ColinC
New Member
Posts:27
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| 28 Nov 2015 12:41 PM |
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Thanks for all of the helpful replies. One thing that probably isn't as clear as it could be from my earlier posts is the basic layout of the floorplan. Here's a diagram that shows the challenge:
https://dl.dropboxusercontent.com/u/1894227/MainFloor.jpg
This shows the main floor where the stove and sunspace inlet are located; the upper/2nd floor has most of its space "sealed off" in separate rooms with closeable doors...if all of these doors are closed then the only thing remaining "open" on the 2nd floor is the 4'W x 16'L x 7.5'H ceiling space (although when running the stove we'll usually leave at least two of the room doors "open" to get some heat in there). The basement has about half of its space "closed off" (storage/shop) while the rest remains open. Again that stairwell openly connects all 3 levels. You can see the problem...the main floor bath and the stairwell are located such that there is only a 4' "passage" through which heat could be moved from one wide of the room to the other without heading up that stairwell. Maybe mounting one of those small "circulation fans" on the ceiling in that 4' wide "passage" might help move some of the ceiling-hugging heat from the stove over to that far side of the room rather than "up" the stairwell? |
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jonr
Senior Member
Posts:5341
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| 28 Nov 2015 04:58 PM |
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The more you can mix/dilute the air coming off the stove before it gets to the stairwell, the less strongly it will want to rise upwards. And of course once mixed, air doesn't stratify to a higher temp. Ie, if the air is mixed down to 80F before it gets to the stairwell, the ceiling in the stairwell won't be above 80F. You want lots of air movement over/across the stove and within the right side room.
Yes, a fan (preferably bigger and slower) blowing down the hallway to the left will help with heating the other room. Since air velocity in this large duct can be low and people don't sit in the hallway, there won't be much draft discomfort. Return air flow (left to right) will be through the staircase area (helping to keep stove heat out of the stairwell). Think large clock-wise circular pattern.
Maybe there are some acceptable looking wall mount fans. |
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3cityblue
Basic Member
Posts:111
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| 29 Nov 2015 09:29 AM |
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Tough problem. I see the low ceiling on the main level as the biggest stumbling block. Since that is the level you want to heat, it would make the most sense to put the ceiling fan there, run it in reverse so the warm air off the stove is pushed out and down the wall to mix with cooler air. This would be the most effective way to address jonr's mixing/dilution insight. Maybe a "hugger" type fan is possible?
Not sure of the effectiveness of a fan in the stairwell but again the idea would be to run it in reverse to push the air out to the walls and down. Hopefully that would not create the draft Dana refers to but would accomplish the mixing. I would mount it on a down rod. You can always move it up once you get an idea of effectiveness, and on a down rod you could use it in normal mode for summer cooling. |
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ColinC
New Member
Posts:27
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| 29 Nov 2015 12:58 PM |
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So even with my unusual situation of a ceiling fan in that 9'x7' 'chimney', a fan would be most effectively running in reverse rather than normal operation 'pushing' the rising warmer air 'down' ?
I do have a circulation fan mounted on the rear of the stove that blows some air 'forward' and mixes air somewhat, as well as one of those 'heat powered' circulation fans that sits on top of the stove...but that fan doesn't move much air so not sure how much it contributes to mixing/distribution...
Posted By 3cityblue on 29 Nov 2015 09:29 AM
[snip]
Not sure of the effectiveness of a fan in the stairwell but again the idea would be to run it in reverse to push the air out to the walls and down. Hopefully that would not create the draft Dana refers to but would accomplish the mixing. I would mount it on a down rod. You can always move it up once you get an idea of effectiveness, and on a down rod you could use it in normal mode for summer cooling.
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3cityblue
Basic Member
Posts:111
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| 30 Nov 2015 09:14 AM |
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"So even with my unusual situation of a ceiling fan in that 9'x7' 'chimney', a fan would be most effectively running in reverse rather than normal operation 'pushing' the rising warmer air 'down' ?"
I would think so. The theory is that while running in reverse a current is created that forces air against the ceiling and then down the walls. In normal mode the air current draws from the side and creates the cooling down draft you feel. A graphic and discussion of the two flows can be found here https://www.quora.com/How-does-the-ceiling-fan-create-air-flow.
In your case, I would think the 'chimney' would enhance the flow down the wall and hopefully not create an uncomfortable draft. |
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ColinC
New Member
Posts:27
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| 30 Nov 2015 07:38 PM |
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Right...I understand the general theory behind the idea. But in my case--even though I called the stairwell a "chimney"--it isn't really much like that. The top of the "chimney" is the top floor. So if the fan is running in reverse, it's pulling warm air "up" and then pushing it down the walls to the hallway/rooms of the second floor, exactly where I don't want it to go. The idea is to try to keep at least some of the warmer air from heading up/pooling on that 2nd floor level.
I'm not really concerned about the "downdraft" issue since no one is ever spending much time in or near the stairwell. The sitting/activity locations tend to be along the "ends" of the house furthest from the stairwell area.
Posted By 3cityblue on 30 Nov 2015 09:14 AM
[snip]
I would think so. The theory is that while running in reverse a current is created that forces air against the ceiling and then down the walls. In normal mode the air current draws from the side and creates the cooling down draft you feel. A graphic and discussion of the two flows can be found here https://www.quora.com/How-does-the-ceiling-fan-create-air-flow.
In your case, I would think the 'chimney' would enhance the flow down the wall and hopefully not create an uncomfortable draft.
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