Room-to-room ventilation (Transfer Fan) privacy concerns
eyremountllc
| Posted in General Questions on
I’ve never used one of these before. When you use a room-to-room transfer fan between a bedroom and a hallway, is the privacy of the people in the room a concern?
Thanks
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Only if they're loud, smelly or do things they don't want broadcast.
Are you talking about the type that goes directly from one room to the other, or the type that has a high grille on one side and a low grille on the other? The second type would block light and reduce sound transmission between rooms.
I am considering the hi-lo type.
Roger,
Most through-the-wall transfer grilles (including the high / low type) don't include fans.
More information here: Return-Air Problems.
This is the one I am looking at
http://www.tjernlund.com/Tjernlund_AireShare_R2R_R2RP_Lit_8500731.pdf
I believe this one does have a blower.
Roger,
My guess is that any transfer grilles, including systems with a fan, increase sound transmission from room to room. But the hum of the fan may disguise the sounds escaping from the bedroom.
Thanks. Those are my thoughts. I was wondering if there was ever a concern and have people experienced opposition to transfer fan because of this issue.
" ... is the privacy of the people in the room a concern?" Yes, unless they don't care. Best privacy is achieved by a jumper duct but only if you can do it through e.g. a closet so that the duct stays in conditioned space. Not cool to take it through an average attic. Hi-lo is next best.
Is this for supply or return air, by the way? If return, and your supply ductwork is properly configured, you shouldn't need a blower. If supply, you need to arrange a return air path also.
Transfer fans are neither supply or return. You use them to take heat from a too warm room to a too cold room. And it doesn't matter what sort of heat system the house has.
The need for return air path is a good point, but the 1/2" gap under the doors usually does the trick.
I agree with James. If you are using these in lieu of a separate return in each bedroom which is the most common purpose, no fan is needed. Looks like these these units you mentioned are to be used in a home where you have a ductless system and you have a bathroom or something that does not get any supply air - in that case the fan can be beneficial.
Kevin,
I must disagree with your statement: "The need for return air path is a good point, but the 1/2" gap under the doors usually does the trick."
To avoid pressure imbalances between rooms, a transfer grille should provide 70 square inches of free area per 100 cfm of supply air ducted to the room. Undercutting a bedroom door won’t solve the pressurized bedroom problem. Even a very large gap — a gap of 1 inch between the finish floor and a 30-inch-wide door — can handle only 47 cfm of return air at a maximum 2.5 Pascal pressure difference. That’s adequate for only a tiny room measuring about 75 square feet.
For more information, see Return-Air Problems.
The house is designed to be a passive house. We have an ERV to "blend" the air and being in the D.C. area we have both heating and cooling loads. We are heating the house with a 1.5 ton point source MiniSplit that will be installed on the first floor in the most open area, the living room. Having not built a PH before, we want to ensure that conditioned air gets into the bedrooms upstairs, especially, the MBR, which due to the glazing, will have the highest heat loss.
The solution we came up with is to put transfer fans (probably the tjernlund level-to-level) to draw conditioned air from the living room to the MBR. I had hoped the 1/2" undercut doors would be enough to take air out but I think Martin is correct, that another method is necessary. We decided to put in a transfer grille on the wall above the door. These fans draw in 75 CFMs each. I hope they are not too noisy.
Martin,
You're right. A transfer fan should have a return air path. All that entails is another high and low grille between the two rooms in question. Another possibility is installing two of the fans blowing in each direction and wired together. The cheapest solution is to leave the door or doors open.
The installation instructions for the Tjernland transfer fan doesn't mention this. That's why I assumed the gap under the door "does the trick". Unless you have central ducts, there's nothing inherently wrong with a pressure difference between the rooms, is there?
These fans are band-aids, but in a well-insulated home heated only with a minisplit or two, they can be a decent solution.
Yes the Tjernland instructions do not mention it. I am new to this too and I think a depressured room is more likely to have moisture issues, not sure about an "inflated room" I hope this works as a decent solution. I like the idea because it's like having extremely short ducts and using the rooms as duct work.
Thanks everyone for your valuable opinions and comments.
Kevin,
Q. "There's nothing inherently wrong with a pressure difference between the rooms, is there?"
A. Well, yes. If a room is pressurized, conditioned interior air is forced through cracks in the building assembly. During the winter, this can lead to condensation within walls or ceilings.
If a room is depressurized, outdoor air enters through cracks in the building assembly.
In either case, energy costs can increase.
I think if you do this you need open the wall cavity and seal all 8 drywall to stud connections. Othwerise you will be blowing/sucking from adjacent wall cavities and the top plate may be connected to the attic thus you would be pushing/pulling more air from the attic.
In the winter you would be sucking cold air off the floor so you may not get the comfort you are looking for.
Thanks Martin for explaining the moisture problems. Looks like either way there's gonna be H2O and a balanced system is the best.
Kevin, I am glad you brought up the cold bathroom issue. I live in a builder grade house that I am just plain cold whenever I am close to an exterior wall. We specified electric radiant floor for at least the Master Bath right now, we are not sure about the others but may put them in too. I agree with you that they will only be on for a very short period of time. I am very glad to hear that this is a workable solution. Thanks!
I also started looking into warm towel bars. Cost is always a concern but I really think the level of insulation this house will have is already chipped away a large chunk of my HVAC costs.
Roger,
It sounds like a good design.
As an occupant of a home similar to the one you're working on, I'll add a comment about comfort that I bet you've already thought about and solved already:
First thing in the morning, if there is no heat source in the bathrooms, they will be the coldest places in the house just when you'd like them to be warm. In the 80's they commonly used an infrared heat lamp fixture in the ceiling to take the chill off. Nowadays the most comfortable (but not the most energy efficient) solution is a warm floor. Heating a bath or two with resistance heat is OK because it's used for such a short time, and you get it right where you want it. Warm the towels somehow, even better.
The cold bathroom problem is compounded a little bit by another phenomenon that I've found in my home. When there are no drafts or cold walls anywhere, we (family of 5) are quite comfortable with a thermostat setting of 63-65F. It might sound amazing, but remember the 72F setting from years ago was necessary only because the interior wall temperatures were in the 50s and the higher air temperature compensated. But when you're naked in the bathroom, 63F air is cold.
Martin, right once again. If your exterior building envelope is tight, pressure differentials are less of a problem, but why introduce a differential when a transfer grille is so easy and cheap?
This may help you prioritize your spending to improve things:
http://www.hvaccalc.com/main.asp
Tamarack, another fan company, seems to understand the pressure balancing issue, and offers inexpensive solutions that also muffle the noise transfer.
http://www.tamtech.com/store/pressure-balancing-ashrae-energystar-hvac,category.asp
Kevin,
Thanks again. I really like Tamtech's solution to this issue. It's inexpensive, clean and simple.