Attic Fan Runs During Winter

Attic Humidity
Is My Thermostat Crazy? My Attic Fan Runs During Winter!

Your attic fan runs during winter because you probably have a humidistat control on your attic fan so it runs when attic relative humidity is too high. The idea is for the fan to draw in dryer air from outside to get rid of water vapor that has risen up into the attic from the rooms through gaps in the vapor barrier or worse through improperly vented bath fans. Sometimes the problem is your furnace humidifier setting.

How do I Set the Humidifier?

Some humidifiers have a thermocouple that senses outside air temperature and changes the setting of your humidifier’s humidistat so you don’t have to. But, if you have to set it yourself, here is how to set it.

Jet Fan Recommends setting your furnace whole house humidifier humidistat by this table to avoid attic dampness from excess room humidity leaking into your attic and condensing on wood and metal conduit. Water-vapor is lighter-than-air and can leak through light fixtures and your wall’s top-plate penetrations. Insulation alone will not stop vapor. Vapor barriers help but usually have gaps. Your attic fan is running in the winter because there is excess attic vapor which is triggering the humdistat to turn on the fan to draw in dry air from outside through static vents in eaves or soffits, roof vents, or attic wall louvered vents.

Whole House Humidifier Humidistat Settings Which Will Help Keep Your Attic and Windows Dry.

Settings for Different Outside Air Temperatures

Above 40° F	40% – 50% Relative Humidity
32° F	30% – 40% Relative Humidity
20° F	20% – 30% Relative Humidity
10° F	10% – 20% Relative Humidity
0° F	OFF

If you see condensation on your window glass your attic is probably already damp; especially if you have double pane glass.

Winter Attic Fan Running is Okay?

Your attic fan runs during winter regardless of the temperature to bring in dry outside air to replace damp attic air and prevent mold from starting in your attic. Your Jet Fan Attic Fan Humidistat should be set to 70 -75% relative humidity. Fan runs less with higher setting. If you hear your fan is running and running for long periods; here are some possible explanations:

What Causes Excess Attic humidity Anyway?

1. House humidifier set too high.
2. Bath fans blowing into attic instead of ducted out.
3. Kitchen fan blowing into attic.
4. Gaps in ceiling and vapor-barrier that allow vapor to rise into attic.
5. Area water-table is high, and vapor is penetrating house through porous concrete foundation or crawl-space floor, rising into attic.
6. Not enough attic intake venting to provide dry air from outside into attic through static vents in eave, roof and attic wall vents.
7. Unusual atmospheric change has resulted in low temperature and high vapor in attic…fan will shut off when weather normalizes.

Get a Quiet Attic Fan: Jet Fan Attic Fans, The World’s Quietest Attic Fans for Homes where Quiet is Important.

Hello Stephen,

Our Jet Fan Attic Fan is only intended for ventilating attics.
The air you want to be its best is the room air…the air you have to breathe day and night. I would recommend that the attic air be sealed off from the house air and that the crawl air also be separate. You can ventilate the crawl space with a crawl-space-fan and the attic with the Jet Fan Attic Fan. Both spaces need to be dry, but you do not want that air running through your house. Keep in mind that vapor barriers have to be on the predominantly warm side of the insulation in wall and ceilings and floors and only one side. Does your HVAC do more heating or cooling? If the answer is cooling then the a single vapor barrier should go toward the outside of the insulation. And the opposite if heating is more common then it should go on the inside heated side of the insulation. One exception is the vapor-barrier you have on the ground in the crawl which you have done correctly to stop vapor before it gets into the space. Additionally, make sure there’s enough static venting in your attic, so when you Jet Fan comes on whether by heat or humidity (with optional humidistat) the “make-up” air will come from outside not from unknown places around the house. Same with any fan for your crawl…it must have “make-up” air from outside not from inside the house.Thank you for your interest in the Jet Fan Attic Fans,Jeff Tideman, “Jet Fan Man”

If you’ve been reading about how attic fans supposedly suck air through your ceiling and all of your air-conditioning with it. Well here’s the truth. If you have a gap in your ceiling some air will go through it. So before you turn on your heater, your air-conditioner, and your humidifier and definitely before you add any more  insulation you should seal all those gaps up. In the mean time just be thankful for the extra oxygen you’ll be breathing.

What I’m not seeing anyone talk about is oxygen. These self-appointed experts who have never been in an attic, let alone 15,000 attics like I have, are obsessing on energy. So much so that life-giving oxygen is flatly ignored. Let’s be reasonable, you need fresh air or your going to die. Seal up your house and stay inside and you’ll be dead in less than a week. I sleep with my window open year-round so I won’t die.

If you read the instructions that come with all attic fans they say that you have to install intake vents to make sure that there is enough intake “make up” air coming in from the outside. Sadly, this just sounds boring and some installers skip this step. Intake vents whether in the soffits, gable walls, or roofs lower the suction in the attic so if  some air is leaking through it’ll only be a very little, just enough to keep us all alive. Open a window a little and you’ll know that the air coming into your house is not coming from the crawl space or the chimney.

Here’s a fact that all these self-appointed experts obviously have never considered; Fact: There is no shortage of energy in the universe. So while my days are numbered, energy will always be here until God rolls up our reality like a scroll. So to me the shortage is in the days of my life, I sleep with the window open so I will live longer and not be like the poor government workers working in government buildings so air-tight they literally get sick.

So get 5 to 10 degrees cooler upstairs by getting rid of the 150 degree attic air that heats your insulation, your rafters, your joists, your shingles and by later in the day backs up and starts to heat you!

Buy a Jet Fan Attic Fan (and follow the instructions so it won’t suck out your air conditioning)

Save Heat – Expert advice from Jet Fan Man:

Saving heat is usually suggested in simple ways: sealing around windows, doors, and the attic access; insulating the attic and foundation walls as possible.
Heat moves three ways: by conduction, convection and radiation. But there’s another way you are losing heat that contractors don’t like to talk about because it’s harder to fix. Water vapor.
It takes heat to make water evaporate and this latent heat is lost when vapor escapes. So by stopping the vapor, you keep the heat. So before you insulate your attic make sure gaps in your ceiling through light fixtures or around electircal conduit are sealed up first.
Vapor cannot be stopped by fiberglass bats or any kind of loose fill insulation. Insulation slows the movement of heat but does very little to slow water vapor that is actually lighter than air and is constantly pushing up rising into your attic through gaps and through the insulation.
Honestly the building industry has not taken this very seriously and it’s time they did. Vapor not only takes heat with it, but when it gets to the cold side of the insulation it can condense and cause mold and rot.
Seal first, then insulate.
For answers to your home questions call:
Jeff Tideman, “Jet Fan Man” for a FREE Consultation.
Phone 630-834-9165