Putting speed control on attic fan

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That is why I never said that his chimney is too large. I only stated that the chimney needs to be correctly sized to the appliance, in this case a water heater.

Answer me this. Have you ever lit a fire in a fireplace? Does the fireplace draw air the same when you light the first piece of paper as it does when the fire is hot? Do you think this principle is unique to a fireplace? Or will a water heater on a correctly sized chimney have a better draft because the hot air stays hot, fills the whole chimney and rises, pulling more combustion products behind it?

Again, you must have a reading comprehension problem. I never said he needs a chimney liner. I only said that if the chimney is too large for what's connected to it, then he needs a chimney liner.

Uh huh.

Don't know what you're talking about here. I've never heard of anyone looking at using a "draft motor" to help the water heater exhaust. I've heard of people buying high efficiency furnaces or water heaters that have them.

So says you, the ignoramus. The NFPA and local codes say that while it isn't rocket science, it is science and there are standards for chimney sizing related to what it's connected to for safety and proper operation. A chimney needs to be in a certain size range. Too big or too small, neither is good.

Not disregarding anything here.

I'll leave it for others to decide who the real boob is here.
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Mikepier wrote:

You've never really stated what problem you have (or you think you have) because of this so-called negative pressure.
The one thing you've said is this:

Does your water heater have a standing pilot, or electronic pilot?
Did you do this match test when the main burners on the water heater were on, or off?

What is the condition of your home's windows and doors?
Do you think you have an ultra-sealed house? A house that's so air tight that the only place that negative pressure can be relieved is through your water heater flue stack?
Is your furnace near your water heater? Does it have open or closed combustion venting (ie - is it high efficiency?).

You really can't have a sealed chamber because combustion air has to be able to enter the pilot and burner area (from somewhere) or you'll get no burning.

What happens when you have the attic fan turned on, and you open a window (a high window - second floor if you have one - you haven't said if this is a single story or 2 story home). What happens with this match test if the attic fan is on and you have a window open?
If you have pull-down stairs to get into the attic, then that's a large area to seal compared to just an access hatch.
But I still wouldn't expect an attic (roof) fan to significantly depressurize an entire house, unless you have the following MAJOR problems:
1) you have insufficient passive soffit or gable venting (you haven't said if you have soffits or a roof overhang)
2) you have gaps in the ceiling that connects your household airspace with the attic airspace (perhaps where interior walls meet the attic, in closets, etc). Generally hard to see areas.
3) Where are interior fans (kitchen, bathroom) vented? Into the attic, or through the attic directly to the outside?
You need to tell us more about 1, 2 and 3. If you're too disinterested, motivated or lazy to come up with an answer to those questions, then you are not really serious about fixing your home and making it right, and all of our efforts here are wasted on you.
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He did in the other thread that he referred to and I think most of us here have read it. Let me help you out:
http://groups.google.com/group/alt.home.repair/browse_frm/thread/9f9b9220ffb7845e?hl=en #

Matters not a wit.

More attitude, eh? Why is this guy's problem of such emotional interest to you?
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Standing pilot

Both, and both times the flame was blown out with the attic fan on

Fairly new

I honestly don't think my house is air-tite, but obviously the attic fan is pulling the air somehow.

I don't believe it's high efficiency. It's a Trane XR80, the exhaust goes out on its own 6" duct, which by the way when I do a flame test on the furnace duct without the water heater or furnace running, the flame gets blown out also.

If I open a window or door, the backdraft problem goes away. Once I close the door or window, it takes a couple of minutes for the backdraft problem to appear again. This is in a 2 story split house.

I have vented soffits, but I mentioned I also have 2 roof vents and a gable vent.

I can't really see anything unusual.

Through the attic to the outside , and they are sealed rigid duct.

You've obviously misjudged me for someone else.
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Is there any path direct from the basement to the attic? A chimney chase? Other chase? Unconnected extra HVAC duct?
It would seem more likely that would be needed to draw significant air from the basement to the attic than for it to happen by going through the living space.
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Mikepier wrote:

The attic fan will help increase the life of your shingles, and it will probably lower by a few degrees the air temp of the upper layer or strata of air near the ceiling under the attic. You don't say if this is a 2-story with basement, single story, etc.

You are wrong.
There is no way that you would be feeling the effects (air currents) inside your house caused by the roof fan - unless you had a massive hole (several square feet) somewhere in your ceiling leading to your attic space.
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Bob F wrote:

I've said that about 5 times now in this thread.
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Mikepier wrote:

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.
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Bob F wrote:

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.
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Ken wrote:

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.
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Open a window.
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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.
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On Mon, 22 Aug 2011 06:35:14 -0700 (PDT), Mikepier

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
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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.
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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.
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Mikepier wrote:

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?
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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. http://www.totalhomeinspection.com/hints_chimneys.shtml
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I hadn't read about your match test, b/4 I posted about the flue size. I would suggest as I seen someone else suggest, open a window or two when your attic fan is on. Then, do the match test at the flue hood of WH. If it doesn't go out, you know you have a deficiency in your thermal envelope.
I would also do a match test with the attic fan running, away from the exhaust hood, with windows closed. Think close to the wall where a _chase_ for the chimney would be.
Depending on the test with a window open, I would start thinking leakage around light fixtures, electrical going into attic through top plates, the pull down staircase for starters.
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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
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Mikepier wrote:

(Amazon.com product link shortened) 1&pf_rd_i00BKQGDE&pf_rd_m=ATVPDKIKX0DER&pf_rd_r3R2NTM0Q87VFEGEJM8

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.
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