How much noice does a power vent make?

We have a moisture buildup in the attic because it appears that the house does not have enough roof vents (four vents for 1,800 sft house with the hip roof).
We would like to install a power vent with a humidistat.
Can anybody tell how much noice such a vent makes? Is it noticeble? How often does it turn on?
What is a good vent brand?
Thanks,
-Stan
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yes they do make noise. It is noticable but for the most part not objectionable. However (in my opinion), you are better off to correct the intial problem (lack of vents) than to try to band aid it with "more power". I have had 3 power vents in 3 houses by 3 manufactures and all three froze up in under 2 years. My bad luck? I don't know but I won't waste my money on them any more. I also worry about them being fire hazards when they freeze up. You are also more prone to ice dams in the winter with inadequate ventilation and power vents don't run in the winter. Do humidistats work in the winter?

hip
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Interesting.. I did not know they freeze up in the winter ...

house
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I strongly suggest you forget the power vent idea and move on to fixing the real problem. The correct fix will be cheaper and work better in the long run.
BTW why a humidity sensor? What is adding moisture to your attic that would trigger it? You should not have anything adding moisture.
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Joseph E. Meehan

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The reason I started considering the power vents is that accorind to the guy who inspected the roof, I need three more vents and two of them on the front section of the house...
Thanks!

house
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While I would consider a second opinion (and fresh ideas) he may be right. Just adding a power vent will not change that however.
It may well be possible to do what is needed and still maintain a good looking roof.
If it were up to me to put up with a vent where it may detract from the looks of the roof or not have it and detract from the function of the roof, I would choose function.
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I agree, but still don't understand why doesn't a power vent solve the problem. It looks for me, that a power vent provides an additional air flow in the same way as a regular vent does, but since it has a motor, I may need less vents.
Of course, if the vent freezes in the winter, I don't want it.
The reason I started thinking about a power vent, is that I found on one web site that a power vent is the best option for the houses with a hip roof.
Maybe it was the web site of a company who sells it ): ....

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My stuff on ventilation says that a power vent does not reduce the amount of free ventilation space. It seem like it would, but that is not what they say. I presume you are talking about a roof mounted fan since you have a hip roof.
The quietness of the fan depends on the roof construction and a lot of factors. My fan makes very little noise and is noticeable in only one spot (about 4 foot by 4 foot) if you listen hard. It mades a bit more noise before I put up a sound reflector/absorber. This was simply a sheet of material hanging 1-2 feet below the fan more or less parallel with the roof and does not interfere with air flow.
The term "freeze up" in common usage means that the shaft binds tightly and stops turning. It has nothing to do with freezing temperatures or freezing water. The vent won't freeze in the winter. Winter, however, does mean that the motor won't turn on, since power vents are controlled by thermostats usually set to about 95 or 95 degrees to turn on. So your power vent definitely won't provide more ventillation in the winter than if you just left the motor out.
Your best solution is to add more ventillation grills in the soffits (smaller more closely spaced are generally better than a few large grills) and add some more passive roof vents. Get a hand out from your local BORG or read the information on a package of asphalt roofing to find out how much free ventillation you need. It is possible that your problem, if real, is caused by the soffit vents being blocked by insulation.
Stan wrote:

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well, let me start by saying that overall, you really do not want a power ventilator. We had one at our cottage in ontario on lake huron (really hot attic). We had friends who also had one, and it "froze" (Motor burnt up). After hearing their story (house caught fire) we installed a manual motor control with a heater coil, so if the motor took excessive power, it would just trip the switch. We came home to the cottage one day, and my 14 year old noticed the switch was "off". He went into the attic and discovered the motor totally frozen, and there was no real cause for the freeze up. The motor was new, and the unit itself was only a year old. Anyway, they are a real pain in the a** and I would not reccomend buying one.
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I've been ran the same power ventilator for 25 year without problems. I believe that most of them have impedance protected motors, mine did.
RB
Al wrote:

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Ventilation is a two part process. First there has to be a vent out to get rid of the air. However for that to work there also has to be vents letting air in.
Another very big factor is the location of the vents. If the locations short circuit or leave dead areas, those areas will not be properly vented. The shape of your roof and attic area in relation to the location of the inlets (lower located vents) and exhaust (high vents) determine this.
I suspect that since the roofer suggested you need some venting on the front of your roof, that there may be a dead area situation and just adding a power vent will not change that. At best a power vent may increase the flow so you can get buy with lest total vent area. It also could create a short circuit and actually reduce the effectiveness of your vent system (although I would believe this is the exception, not the rule.
In short, I suggest having someone who knows what they are doing take a look at your situation and make a second recommendation so you can confirmed the first of put it in doubt.
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Joseph E. Meehan

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Stan wrote:

I've got one to reduce the temp in the summer. I can hear it, but only if I listen for it.
I am curious if you've tried to identify the source of the excess moisture. Generally, one gets moisture problems when warm, moist air hits a cold surface. Adding extra vents certainly will help remove the moist air faster, but one has to wonder why it is there. Have you looked to see if any of the bathroom fans, or other fans, are venting into the attic?
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