You can get an idea by putting a thermometer in the attic and recording some temps with and without the fan on similar weather days. Also record the outside air temp. One of the wireless thermometers would be ideal. You can't compare it exactly, but I think if the fan is going to be worth it, you should be able to see some consistent and noticeable difference in temps.
I've never seen one of these cycle on and off on a hot sunny day. They come on and stay on until the sun goes down or the weather changes, eg clouds roll in. The sun generates a tremendous amount of heat. I think the best they are capable of doing is keeping the max temp that would be reached lower.
I suspect that there are fewer soffit vents than would be indicated for a ridge vent. It would also be good to make sure that the soffit vents that are there are not covered, even partially, with insulation.
A fan that's noisy or vibrates is a motor that needs to not be functi> > My townhouse in the northeast has a ridge vent plus soffit vents. It
You buy a vent fan, "permanently lubricated bearings" for maybe $35-50. Wholesale price is less, manufacturing costs obviously way below retale. Motor sits in an environment that we already know to be hot, hostile to a motor's operation. And we ignore it till the next time the roof needs to be replaced, or until it starts making noise. But are you going to be checking it if it seizes up and continues to try to function, because its overtemperature cutout failed to perform its function? Of course not, because you wouldn't know. But generally, the heat generated by it trying to function is sufficient to cause internal shorting and for it to be shut down because of that. So, if you really must bypass the function of a ride vent, I suppose a roof fan is a relatively harmless way of doing it.
My townhouse in the northeast has a ridge vent plus soffit vents. It also happens to have a roof fan not too far from the ridge. I have the fan's thermostat set at 110 degrees. On a perfectly sunny, and relatively calm, spring day in the mid 60s or higher, the fan will turn on early in the afternoon and not ever shut off until toward the end of the afternoon. (there are no trees to block the sunlight until later in the afternoon).
I've heard that having a roof fan near the ridge is less than ideal, because they tend to draw air in from the closest source which is the ridge vent. When I put my hand up to the soffit vent, by sticking my hand out the window, it did feel like the fan was helping suck air in through the soffit (a little bit) relative to when the fan was off, but we're not talking much flow here. When it was calm outside, it seemed a small piece of Kleenex would tend to stick to the soffit more when the fan was on vs off, although the Kleenex would still tend to stick somewhat even without the fan. Bottom line is that I believe the fan is sucking some extra air in from the soffits relative to when the fan is off, but it did not seem like very much.
1) Do you think that this fan is likely helping enough to justify using the electricity? On a perfectly sunny spring day, it is not shutting off until the end of the afternoon, and the thermostat is the kind that cause would shut it off if it were to cool down a only by a couple of degrees. At best, this fan may be preventing it from getting even hotter than 110 degrees. I suppose I could try taking temperature measurements, but 'm trying to avoid going up there when it 110 degrees.2) One other question: this roof fan's motor is somewhat noisy, and I can feel vibrations if I put my hand on the walls of the living area below the attic? Could these vibrations from the fan's motor potentially cause any harm to the roof, etc, or are they harmless?
Anyway, It's too bad that the ridge/soffit system alone isn't enough to prevent my attic from reaching 110 degrees or higher on a perfectly sunny spring day. What do you think?
Thanks,
Jay
Check out the thread Subject: Roof Mounted PW Vents Worth The Electricity?
Thanks. Everyone seems to have a different opinion as to whether the fan is worth the electricity.
As an experiement, I may try setting the fan's thermostat 5 or 10 degrees higher, and seeing if that causes the fan to cycle on and off on a very sunny day, rather than staying on for hours at a time. It would seem to me that if the fan were actually making any worthwhile difference toward cooling the attic's internal temperature (compared to just letting the soffit/ridge vents do their work passively), then, if the thermostat were set high enough, the fan should cycle on and off a couple of times on a sunny afternoon than just staying on until the end of the afternoon. The fan's thermostat doesn't seem like it has much of a differential between on/off, so if it doesn't ever cycle more than once, then the fan isn't cooling the attic much. If, even when set all the way up to 120 degrees, the fan turns on, but still can't cool the attic enough to cause the thermostat to cycle off and then on again a couple of times on one sunny afternoon, then I question whether the fan has any real cooling benefit.
By the way, today I made the fan significatly quieter by temporarily shutting off circuit breaker, and then bending some of the blades that had been out of balance. It's still not super quiet, but is substantially better than before I made the adjustment.
Jay
Soon, I will be putting on a new roof, and installing a new ridge vent. Several highly-regarded roofers advised me to either scrap my fan, or the ridge vent. I have a ridge system now, and it seems to do a decent job. The power ventilator, mounted near the ridge vent, has not worked for about 15 years. Like you, I was told that the fan probably drew most of its air from the ridge, rather than the soffits.
Based upon expert advice, and my experience, I am having the fan removed and it's hole covered. I will be installing a few more soffit vents. Tom
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