Attic fan/humidistat question

[Dave]

Hello, An attic fan has died (moment of silence). The device that is currently installed is a thermostat-driven electric exhaust fan. I'm looking to determine whether the fan even needs to be replaced or to simply leave the opening as-is as a passive vent (it looks like the motor cannot be removed without going on the rooftop, which may not be an option). The details are:

- The house is in Western NY.

- Insulation was professionally installed in June into the attic.

- Last summer, the temps climbed into the high 80's-90's for maybe a week or two with the attic reaching ~110-120 for maybe a handful of days.

- The winters can be cold for a few months.

- There appears to be adequate soffit vents to the attic area.

I'd like to determine the need before the brutally cold weather hits, but I am looking for more specific information related to temperature, humidity, etc. With the additional insulation and the short time within the house, I do not have current visual gauges regarding previous moisture. There does appear to have been previous moisture issues but the insulation that was in the house had been improperly installed.

My questions are:

1. I understand from other posts that temperatures that reach ~120 or higher can be the beginning of the damage-inducing range. Is this over generally considered the norm in hot climates (i.e., 120 all summer), or an "if it ever reaches, assume the worst" guideline?

1. Is the rule-of-thumb in the NE to get a humidistat? I was thinking of buying a bare-bones humidistat and just recording the values over a few weeks, but have not found a guideline (i.e., if it is consistently above x%). Or, would visual inspection be enough (i.e., if you see moisture, get a humidistat, if not you should be fine)?

Am I overanalyzing this to to death? Probably. I apologize.

TIA, Dave

[m Ransley]

In winter passivly vent, if you have signs of condensation or mold increase venting, attic temps should be near outside level. A drawback of powered vents is removing conditioned interior air because makeup vents are to small and most attics are not sealed from the lower area.

[Joseph Meehan]

I suggest first making sure you have good passive venting and that leaving the fan in place is not going to short circuit the passive venting. In most situations passive venting does a very good job if properly designed. Power venting is seldom required except where the passive venting was not properly designed or is defective in some way.

Next time you re-roof eliminate the old fan.

[Dave]

Thank you. There is no air conditioning in the house, which is probably why I forgot to mention it.

Thanks, Dave

[Chet Hayes]

I agree, it depends on what other outlet vents there are besides the power fan. I think a ridge vent combined with soffit vents is the best solution. If you only have two gable vents, then it's likely the fan will be a help in the summer. As far as humidity goes, you can get by with less ventilation than that required for heat removal. In a northeast climate, I have yet to see an attic where a fan was needed for humidity issues. If you have any humidity issues, I'd check to make sure there is no source for humidity, like bathroom or dryer vents that improperly terminate in the attic.

And I'd have to disagree with an earlier post that said the attic temps should be near outside temps. On an 85 degree day in full sun, this isn't realistic. The temp goal of attic ventilation is to prevent extreme temps, like 120+, which can lead to premature roofing failure and increase air conditioning reqts. It's not unusual for a properly vented attic to be over 100 on a hot day, which the the insulation can easily handle