A few weeks ago I posted a problem with too much negative air pressure in my house caused by my attic fan. The motor I have on the fan is similiar to this.
If you have negative air pressure in your attic, why don't you simply add a few more vents? There are probably eaves where a vent could be added reducing the pressure.
As far as controlling the speed of the fan motor, I think DC motors are better suited for such control. Of course you could reduce the AC to an AC motor, but it can present problems for the motor.
Open a window.
DC motors are
That's the problem, I think I have adequate vents. I have 2 roof vents, and a gable vent. I'm not sure if adding another vent would fix it.
Air over fan motors are cooled by the air the fan pulls. Slowing one down in a place out of sight is a scary proposition even when thermally protected. I am guessing the living area is air conditioned otherwise you would just open access to the attic .
Finding a slower replacement motor might be a better option.
Without getting to that point, I'd say that the desirability of those fans is that they move vast amounts of air. I wouldn't slow that process down.
The problem is in the basement. I'd address it there. If leaving a window open isn't an option, then a small vent bringing some outside air in would cure it.
If you've got a furnace down there, it is even more important. *It* will also benefit from an unrestricted amount of air for combustion.
Jim
There's a couple things going on here.
Normally, an attic space is supposed to be sealed from the house and air isin't supposed to move between the attic and interior house air space. Now, sometimes people put a fan in the ceiling to pull air from the house and push it into the attic, which is useful to pull cooler exterior air into the house to cool it down in the evening when there isin't enough of a breeze to accomplish that. The OP doesn't say where the fan is placed. The picture he shows is typical of a roof-mounted fan, but I suppose could also be a house exhaust fan.
So if this is a roof-mounted fan, then the house shouldn't experience a negative air pressure, and any air infiltration into the attic should be sealed. It's hard to imagine that there wouldn't be enough soffit or gable-end venting to allow proper attic air flow and air balance.
If this is a house exhaust fan that's exhasting air into the attic, then it's normal to expect a negative air pressure in the house if you don't open any windows to allow proper air balance. The whole point of having a house exhaust fan is that you must allow exterior (outside) air into the house to balance the airflow.
I have a ceiling fan that's connected to an ordinary wall-mounted dimmer switch (mainly to dim the lights that are part of the fan unit) but the dimmer does change the fan's RPM along with the brightness of the lights.
The downside of having a speed-controlled AC motor is RF noise created by the controller or dimmer that gets injected into your power lines and can mess up AM radio and sometimes OTA tv reception.
The solution is not to put a speed controller on the fan motor. The solution is to allow proper air balance.
Are you talking too much negative pressure inside the thermal envelope? If so, the problem is your thermal envelope isn't _tight_. Slowing down the attic fan isn't the solution to fixing the envelope problem.
This is a roof mouted fan, not a whole -house fan.
I don't have issues with my furnace since in the cold weather, the attic fan is off anyway. Its my water heater I have issues with.
I have a pull-down attic stairs in the second floor hallway. I know it's not 100% sealed, but for the most part its pretty tight.
I already asked about this, but I'll try again. You just put in the water heater, right? You posted about venting, but I don't know what you did. Did you change the venting? Did you have a problem with the old water heater pilot? If not, you should look at your venting. I've got no idea how you let that water heater chase you up to the attic.
--Vic
Don't you have any soffit vents? Reread the book on attic venting and follow the best practices and the problem should resolve itself.
Joie
I really have to wonder how you know that you have a negative pressure issue when the attic roof fan is running.
Unless you have a really small attic space, or you know that your doors and windows and walls are really well sealed, I would think that most homes are leaky enough so that a single roof-mounted attic fan can't cause a negative air pressure situation inside the house.
Do you know if your kitchen (stove) or bathroom exhaust fans run straight through to the outside? Or do they exhaust directly into the attic? If they do (exhaust into the attic) then that's where your connection is between the attic and household airspace is.
Do you have a whole-house (built-in) vacuum cleaner system?
What sort of HVAC system does your home have? Does it have a makeup air intake or combustion air heat exchanger? Is it open or closed?
Gas water heater?
Fire place / wood stove?
Hmmm, You think about only output side, think about input side of the air movement. Law of physics. Often times even vent size is not adequate. What kind of soffit do you have? Now you are not venting the attic, you are venting the house.
Why are all of you (except MK) overlooking the fact that he should not be drawing interior house air into his attic in the first place?!
Yes, most probably he needs more attic venting, probably lower down towards the soffit (he doesn't even say that he has soffits). I'm guessing he has no roof over-hang at all.
But a roof fan shouldn't be able to create a negative pressure in the house. I'd like to know more about what observations or measurements he's made that makes him think he does have a negative pressure caused by the roof fan.
Encouraging him or giving him pointers about a fan speed controller is stupid and is a bad tangent to follow here.
on't you simply
ink DC motors are
I thought I answered this last time, but the water heater is vented through an exterior brick chimney. Its not going through the attic at all. And the water heater is right underneath the chimney vent, so total length of ducting from the water heater to the chimney is maybe
1 - 1 1/2 feet
Hmm, I don't think I saw an attic fan under speed control. Most are on thermostat switch which turns fan on or off depending on the temp. inside the attic.
You don't say if you changed the HW vent, either location relative to the furnace vent, or angle of entry into the chimney, or went to a different size. And whether you had the problem with the previous tank. I'm no expert on venting HW tanks. I've always left them as I found them. But you were talking about changing the venting. If you did, that's where I'd look, not the attic. Besides blowing out the pilot, wrong flue draft is a safety issue.
--Vic
Vic, the venting is the same, I changed nothing. It is a 3" rigid duct (per water heater spec) that leaves the water heater on an upward pitch and goes directly into the chimney. It is not tied into the furnace vent, which is on a seperate duct run. The water heater was installed in January. I first noticed problems when I started using the attic fan in the summer. If I do a match test by the draft hood with the attic fan on, the flame is blown out. After I shut off the attic fan, the flame test is fine, no issues.
This is the one on Broan's website
You also may want to look into sizing of the flue, meaning the chimney is _too_ big. It may have been ok for the previous WH, but not this one. Here's an article, which explains it better. Around here, we are not allowed to vent into a brick or masonry chimney.
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