Fans in the Attic Do They Help or Do They Hurt Theres a lot of confusion surrounding attic fans.Here at GBAGreen.Building. Advisor.How Much Does It Cost To Install A Chimney Damper' title='How Much Does It Cost To Install A Chimney Damper' />Whats the purpose of the fan in my attic How often should I run it Do I need a bigger fan Before addressing these recurring questions, its important to define our terms.GRAPHIC_FireplaceRetrofit_1114_BethGoode_0.jpg?itok=-QTzjRsh' alt='How Much Does It Cost To Install A Chimney Damper' title='How Much Does It Cost To Install A Chimney Damper' />First, we need to distinguish between three different types of ventilation fans.The most common kind of residential ventilation fan is one used to provide fresh air for building occupants.Examples of this type of fan include the fans in a heat recovery ventilator HRVHRV.Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air to air heat exchanger a similar device, an energy recovery ventilator, also transfers water vapor.HRVs recover 5. 0 to 8.In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air.ERVERV. The part of a balanced ventilation system that captures water vapor and heat from one airstream to condition another.In cold climates, water vapor captured from the outgoing airstream by ERVs can humidify incoming air. Workshop Manual Renault Clio Download Youtube there. In hot humid climates, ERVs can help maintain but not reduce the interior relative humidity as outside air is conditioned by the ERV., as well as some types of bathroom exhaust fans.For more information on this type of ventilation fan, see Designing a Good Ventilation System.Whole house fans are sometimes confused with ventilation fans that provide fresh air.Unlike a ventilation fan, a whole house fan an attic mounted fan that exhausts air from a home at night is designed to cool a house that is, to lower the indoor temperature.A powered attic ventilator has a different purpose it is designed to lower the temperature of an attic by exhausting air from the attic and replacing attic air with outdoor air.At the risk of oversimplifying, whole house fans are good.Fans in the Attic Do They Help or Do They Hurt Homeowners in hot climates need to understand the difference between wholehouse fans and powered attic ventilators.Little children had to work as chimney sweeps in horrible conditions for their master sweep and as a result many developed lung conditions and died very young.Powered attic ventilators are bad.Whole house fans.Whole house fans are used to cool a house at night, when the heat of the day has passed and the outdoor temperature has dropped enough to feel comfortable.When should you turn on a whole house fan The answer depends on your climate and your comfort range.The outdoor temperature should certainly be below 8.F or, better yet, below 7.F. The main advantage of using a whole house fan instead of an air conditioner is to save energy.A whole house fan usually draws between 2.If evenings are cool enough, its fairly easy to lower the temperature of your home and your furniture with a whole house fan sometimes in less than an hour.Whole house fans are intended to be used in homes that are not air conditioned.It makes no sense to introduce lots of potentially humid exterior air into a house at night if you intend to turn on an air conditioner the next day.If youre using your air conditioner, keep your windows closed, 2.Cooling load that results when moisture in the air changes from a vapor to a liquid condensation.Latent load puts additional demand on cooling systems in hot humid climates.In most cases, a whole house fan is mounted in the attic floor, above a rectangular grille in the ceiling of a central hallway.Once the outdoor temperature cools down usually in the evening or early morning the homeowner opens a few downstairs windows, closes the fireplace damper, and turns on the fan.The wall switch that controls a whole house fan should be properly labeled so that it isnt accidentally turned on during the winter.The fan pulls air from the hallway and blows it into the attic.Since whole house fans are relatively powerful they are usually rated between 2,0.Once the house has cooled off, the fan can be turned off and the windows closed.Most people who have whole house fans keep their windows closed from early morning until evening, so that the cool air inside the house doesnt escape.You need enough attic vents to let the air escape.Since a whole house fan blows all of the hot air from the home into the attic, the fan wont work effectively unless the attic has large openings to exhaust the hot air.Most old fashioned whole house fans require more attic venting than the minimum amount required by the building code anything from a little more to about twice as much, depending on the size of the fan.Heres the rule of thumb you need one square foot of net free vent area for every 7.The vent area can be made up of a combination of soffit vents, ridge vents, and gable vents.If the vent has insect screening, remember to make the opening 5.Its better to have too much vent area than not enough.Manufacturers of ridge vents and soffit vents provide information on the net free area of ventilation per linear foot of their products for example, the Air Vent website lists different ridge vent products that provide between 9 and 1.How do you size your whole house fan The traditional recommendation is to choose a fan that can move between 1.ACH stands for Air Changes per Hour.This is a metric of house air tightness.ACH is often expressed as ACH5.The term ACHn or NACH refers to natural air changes per hour, meaning the rate of air leakage without blower door pressurization or depressurization.While many in the building science community detest this term and its use because there is no such thing as normal or natural air leakage that changes all the time with weather and other conditions, ACHn or NACH is used by many in the residential HVAC industry for their system sizing calculations.If youre aiming for 1.If your ceiling height is between 8 and 9 feet, just multiply the floor area of your house by 3 to obtain the cfm rating of your fan.Where does a whole house fan make senseIf you live in the right climate, whole house fans are a great way to keep your house cool.In the U. S., they make more sense in the arid West than in the humid Southeast, since most homeowners dont want to invite lots of humid air into their homes.Whole house fans make sense in areas with cool nights.If you live somewhere where the temperature stays in the 8.However, even if you need to seal up your house and turn on your air conditioner during the hottest months of summer, a whole house fan may be useful during the spring and fall seasons, when nights are cool but days remain hot.A few caveats. Whole house fans make sense in some, but not all, homes They dont make sense for homes in neighborhoods where security concerns prevent homeowners from leaving their windows open.They dont make sense for homes with a furnace or water heater in the attic.Because they depressurize a home, whole house fans can cause atmospherically vented appliances located inside a home for example, a gas fired water heater to backdraft.If the homeowner remembers to open plenty of windows before turning on the fan, backdrafting.Indoor air quality problem in which potentially dangerous combustion gases escape into.But the best way to avoid backdrafting problems in a house with a whole house fan is to make sure that the house doesnt have any atmospherically vented combustion appliances.Whole house fans represent a big hole in your ceiling a hole that is likely to leak a lot of heat during the winter unless it is properly sealed.Finally, it should be noted that some homeowners complain that whole house fans are noisy.However, newer models of whole house fans especially the Tamarack HV1.Sealing up the big hole.There are two ways to address the big hole in the ceiling problem.One solution is to build an insulated box that fits on top of fan.The main disadvantage of this solution is that you have to climb up into the attic twice a year to install it and remove it.One document posted online Whole House Fan includes instructions for building a box cover for a whole house fan.Unfortunately, the document suggests that its acceptable to build a cover insulated only to R 5.Clearly, thats not enough insulation.For a better approach, make a site built cover as shown in the detail in GBAs CAD detail library.Or you can follow the advice given by Erik North in his blog on building a coffin for insulation pull down attic stairs.North advises building a box with an R value.Measure of resistance to heat flow the higher the R value, the lower the heat loss.The inverse of U factor.
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