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We discuss attic fan installation cost, practical tips and when and if to hire a contractor. We also included up to 4 free contractor quotes.
An attic fan is a powered ventilator designed to regulate the temperature and heat build-up in an attic or the whole house depending on what type you choose. It does this by collecting the hot air and exhausting it through vents in:
A gable wall. These are the two ‘A’ shaped walls at both ends of a roof. A hole is cut in the wall large enough to take the exhaust side of the fan.
The roof surface. These are the two angled surfaces usually covered by slates, tiles or shingles. Some of the roof covering is removed and a vented cover is fitted to allow the fan to discharge
The ridge. This is the line along the middle of the roof, where the two roof surfaces meet at the highest point. Existing ridge tiles can be removed and special ventilated ones can be fitted.
The fan can either be seated on the floor of the attic and the air routed through a duct to the roof vents or the fan can be mounted on the roof rafters and draw hot air directly from the roof space and discharge through the roof vent. Cooler air will be drawn in through ventilation ports located around the roofspace usually at the soffits although other positions are used as well.
The fan is controlled by a thermostat which turns on and off depending on the temperature of the air in the roof space or can be controlled by a manual switch (or both).
There are two kinds of attic fan:
A whole house fan. This type is often confused with ordinary ventilation fans such as found in bathrooms and kitchens. Their purpose is to remove hot air from the house (usually at night) and discharge into the attic where vents transfer the hot air to outside. A whole house fan is installed in the floor of the attic where a hole is cut to allow the fan to draw air from the living areas. Usually, a grille or grating is fitted in the ceiling to prevent insect invasion.
A powered attic fan. This type is designed to remove hot air from the roof space and replace it with cooler outside air. The fan can be installed on the attic floor and vent to outside via a duct or be fitted to the rafters and discharge directly to outside. There should be no contact with the air from the living space at all.
Whole house fans are used to cool the whole house at night. After the sun has set and the outside temperature cools below 70°F (21°C) the whole house fan removes the heated air from the house, usually at a cheaper cost than a normal air conditioner does.
|Comparison of energy consumption of whole house fan vs air conditioner|
|Whole house fan||Air conditioner|
|200W minimum||2kW minimum|
|700W maximum||5kW maximum|
The removal of the hot air forces cooler air to enter the house from outside through windows, doors, and vents.
It is better to use a whole house fan rather than an air conditioner because you are introducing a lot of humid air from outside. This would be counterproductive if on the following day you turn on the air conditioning to remove this moisture. Anyone with air conditioning knows that you keep the windows and doors closed 24 hours a day so that you don’t increase the amount of moisture in the air causing an extra load on the conditioner.
The fan is mounted on the floor of the attic above a grating in the ceiling of a centrally located room such as a hallway. Once the outside cools sufficiently to gain some benefit from the fan, the homeowner opens some windows and turns on the fan. The fan then pulls hot air from the living area and discharges it into the roof space where it is discharged to outside via covered vents. The total cross-sectional area of the vents is designed to match the capacity of the fan so that a positive pressure does not build up in the roof space. As the fan draws the hot air from the living space it is replaced with cooler air from outside. The fan is allowed to continue working until the temperature in the living areas equal to the outside temperature. The fan is then turned off. If you have a whole house fan it is a good idea to keep your windows and doors closed during the daylight hours to prevent losses of the cooler air already in the house.
The design of the roof vents is crucial to prevent a build-up of humid air in the attic, causing the damp problems that humidity always brings on. The fan will have a specific capacity and this must be matched by the total cross-sectional area of the roof vents. A qualified fan installer will be able to calculate the required vent area needed for your particular fan. The total vent area can be made up of a combination of soffit vents, gable vents, and ridge vents. If you have insect screening on the vents (and I recommend that you do) you will have to account for the reduction in area due to the screening by increasing the vent openings by approximately 50%.
Powered attic fans are usually mounted directly onto the gable wall or sloped roof surface although theoretically they can be mounted anywhere within the roof space and connected to the outside via a length of ducting. Most attic fans are controlled by thermostat although they will always have a manual isolator switch.
The purpose of a powered attic fan is to cool the roof space by removing the hot air and theoretically replacing it with cool air from outside. In practice, however, sometimes the external air is not cooler than inside the roof space.
The idea is to save on energy costs by reducing the amount of work the air conditioner has to do within the living space. Hopefully, the cost of running the fan will be less than the cost of the power required to operate the air conditioner.
In theory, this sounds like a good idea but in practice, it is very difficult to predict where the replacement air will come from. Ceilings are very rarely airtight and the attic fan, in depressurizing the roof space, sucks in air from wherever it can find it. Usually, this is conditioned air coming from the living area into the roof space via light fittings and ceiling cracks. We then have a depressurized living area which will suck hot humid air in from outside through other cracks. The result is that the air conditioner has to work harder to condition this outside air.
Even if you go around sealing off all the leaks between the roof space and the living area, the attic ventilator will still use more electricity than it saves. This will usually cost you more money unless you have the fan powered by a photovoltaic solar panel. More about that later.
There are a few ways to power your attic fan:
There is a considerable amount of metal incorporated within the fan and its ancillaries so the whole unit will require electrical grounding (earthing). Usually, the motor will already be grounded by means of the electrical cable providing the power but it will also need the housing and any other exposed metal parts grounded because of the risk of lightning strikes to the roof.
During the day hot air builds up in the roof space from the action of the sun on the roof surface. The hot air can sometimes reach a temperature that can damage items stored in the attic. The heat can also transfer down through the attic floor to the rooms below if the insulation is not good enough.
Venting of the hot air from the attic produces a negative pressure within the roof space. The negative pressure quickly fills with cooler air from elsewhere. If you have an attic fan fitted you will also need vents allowing outside air into the attic. The size and number of the vents will depend on the capacity of the fan.
That is the theory anyway. In practice, however, the fan tends to draw air from the rooms below through lighting fixtures and other cracks in the ceiling. If the air in the house has been conditioned and cooled this can lead to wastage of cooled air and hence counteract the energy savings that have been gained from the forced cooling of the roof space.
There are three main questions here:
The most important question is whether attic fans are safe to use in a dwelling. If a fire started in the house, an operating attic fan could make the fire worse by:
If the fan and ventilation system has been designed correctly, there will be an automatic shutoff to close the vents and turn off the fan in case of fire.
In places where home security is an issue, householders with a whole house fan may not feel safe leaving their windows open all night long.
If you have an atmospherically vented appliance located in the home such as a gas-fired water heater, the de-pressurization of the house caused by a whole house fan may cause problems due to a backdraught. The backdraught will cause an increase in carbon monoxide venting into the living area. This is very dangerous as carbon monoxide can cause unpleasant side effects similar to influenza, in more severe cases the gas can cause, vomiting, unconsciousness, and death.
The question of whether the attic fan will save you money depends on where you live and the type of climate you normally have. People living in arid areas will have hot days and cool or cold nights. For these people a whole house fan is ideal. For people living in hot and humid Southeast USA, you will not want to introduce humid air into your home and the nights are not really much cooler than during the day. Basically, whole house fans are good when you have cool nights otherwise they aren’t much use.
Because you effectively have a giant ‘extractor fan’ fitted, you will have a big hole in the ceiling. This will cause insulation problems with heat loss during the winter. A solution for this is to fit an insulated box in the roof space which completely covers the fan during the winter. During spring you will have to go up into the roof and remove the box before you need to use it. Similarly, in the autumn you will have to go back up into the roof and refit the insulated box. If you don’t like the idea of manhandling a box in the roof while battling with rolls of fiberglass insulation, you can contact one of the larger whole house fan manufacturers who have already sorted this problem and will sell you a fan already fitted with a solution.
We mentioned earlier that overall the use of a powered attic fan can cost more to run than it saves. The only exception to this is when you have the fan powered by a photovoltaic solar panel. In this case, the electricity is free so the only losses are the increase in air conditioning costs. Even if we forget about the increases in air-conditioning costs, the solar panel won’t stop carbon monoxide back-draughts, will it?
So, to answer the three questions we stated at the beginning of this section:
An attic fan of whatever sort is safe as long as you also fit emergency cut-off switches and ensure enough ventilation to prevent backdraughts.
A powered attic fan is economically viable as long as you stop conditioned air from being drawn up into the roof space, have enough attic ventilation area to prevent roof depressurization and you power it by a photovoltaic solar cell. A whole house fan is economically viable as long as it isn’t used at the same time as the air conditioning and you enclose it in an insulated box during the winter.
A powered attic fan doesn’t really cool a roof space, it just changes the air. It does prevent condensation (see section later on in this article). A whole house fan does cool the house as long as you follow the correct ventilation procedures.
So far everything we have said points to the idea that a powered attic fan isn’t worth investing in except in very rare cases. So how can we keep our attics and roof spaces in general cool during long hot summer months?
Firstly, unless you have air-conditioning ducts or other HVAC equipment in the roof then a hot attic isn’t always a problem unless you want to store candles up there! After all, you should have a thick insulation layer on the attic floor to stop the heat from conducting through to the living space.
If you do have air conditioning ducts in the roof then there are three solutions you can try:
In all cases when dealing with ventilation, you must always get the advice of a qualified HVAC technician.
So far it seems like powered attic fans are just no good at cooling a hot roofspace. All the evidence and there has been a lot of research done on this, tends to show that an attic fan only cools the roof space by drawing conditioned and cooled air into the attic from the living area. But how about if the fan did something else that was useful? How about thinking of the uses of a powered attic fan in a temperate climate like in the UK, a climate that has air carrying a lot of moisture?
In the UK and other countries with similar climate, the main reason for thinking about installing an attic fan might be to try and reduce the accumulation of moisture in the roof space by condensation.
Before we start talking about a powered attic fan removing condensation it would be a good idea to describe condensation and why our houses are full of it and what happens when we have it.
You probably already know that warm air can hold more water vapor than cold air. Condensation takes place when the water vapor in the atmosphere cools to below a certain temperature (known as the dew-point. This is the temperature at which the vapor changes from a gas and becomes a liquid).
We create water vapor in our homes by cooking, showering, boiling the kettle and even breathing. The water vapor disperses around our homes until it reaches somewhere colder than its dew point or is vented to the outside.
We can hear a person asking how come we get water vapor in the roof space when we don’t do anything which produces water vapor there. The answer is that no ceiling is airtight. There are gaps around light fittings, most ceilings are made from plasterboard which absorbs water from the atmosphere and there are always cracks, even hairline cracks where panels join and movement takes place.
Basically, our ceilings are no good at stopping water vapor and eventually the air from the living spaces below ends up in the space under the roof.
We now have a problem. Most attics are constructed with the insulation covering the downstairs ceiling and the roof surfaces above are therefore cold (we are talking about temperate climates remember). This means that any water vapor that gets past the ceiling, light fittings and access hatch automatically comes up with a great big cold surface on to which the water vapor can condense.
There are many ways to stop condensation from becoming a problem in a roof space and most of them are not relevant for discussion today. The only way that is relevant to today’s article is to install an attic fan. As we have already found out, an attic fan is a simple machine that just needs a power supply, a switch and enough ventilation into the roof space to replace the air being discharged by the fan. A simple alternative for this would be to just fit a vapor barrier to prevent any moisture from getting into the roof space in the first place.
So far it seems like powered attic fans are not a good thing to have whereas whole house fans can be an asset. If however, we decide to go ahead and have one installed who should we call and what should we do?
Well, installing both kinds of fans; the whole house fan and the powered attic fan is a tricky job for the amateur to do. Always use a professional HVAC technician who will be able to take the appropriate measurements of your attic, estimate the heat transfer across the roof surface and the amount of heat that would be stored within the loft, install the dedicated wiring and fit the necessary vents. He will also be able to calculate the size of vents needed for both types of fan.
For the moment let us assume that you want a whole house fan. If the one you chose does not come with a sealed and insulated cover for the winter then you should either buy one or build one. If you have a choice however it is always better to buy a fan with a made-to-measure cover supplied by the manufacturer. Don’t forget that a whole house fan can be used in conjunction with air conditioning as the weather changes from hot and humid summer into the cooler but still humid winter, as long as you don’t use them both at the same time. Don’t forget to provide enough ventilation in the living area so that back draughts do not occur pulling harmful carbon monoxide from the gas-fired appliances into the living areas.
Another fault of whole house fans not previously mentioned is that they can be very noisy especially if they are of the older types or if they have been poorly fitted. The solutions to this problem are as follows:
If you already have heating and air conditioning fitted in your home and have the ducts necessary for the smooth running of these systems, you may be able to incorporate these into the whole house fan extraction system. Once again this is something that will need a HVAC technician to decide whether the idea is feasible.
Ok. We have talked all we can about what attic fans are, what they do and why. Let us now talk about the costs involved and the factors that influence those costs.
The costs will vary depending on the size of the fan. Larger fans will move more air than smaller ones and as stated earlier it is better to have a larger fan moving slowly than have a smaller fan moving quickly.
Installation costs will also vary depending on these main factors:
As stated previously an HVAC technician will be needed to do the calculations for sizing the fan and for installing the unit. In addition to this, you may need other contractors to do different aspects of the installation such as:
For these jobs, you will need licensed and insured contractors such as a carpenter, roofer, and electrician. If however, you decide to hire a fan installation company they will probably have installers who are licensed to do all these tasks.
The typical average costs for installing a powered attic fan are as follows. Bear in mind that these are indicative only and are shown only as a guide.
|Costs to install powered attic fans|
|Typical range||$350 to $800|
The typical average costs for installing a whole house fan are as follows:
|Costs to install a whole house fan|
|Low end||$700 to $1000|
|High end||$2000 to $3000|
|National average||$1200 to $1900|
Typical costs of materials and equipment will vary depending on the size of fan and amount of ventilation needed:
|Typical average costs of equipment for powered attic fan|
|Roof or ridge mounted fan. Mains electricity powered||$50 to at least $400|
|Gable mounted fan. Mains electricity powered||$50 to $300|
|Solar photovoltaic powered attic fans||$200 to at least $500|
|Typical average costs of equipment for whole house fans|
|Whole house fan||$300 to at least $1400|
|Typical average costs of equipment for whole house fans|
|Whole house fan||$300 to at least $1400|
|Other materials and equipment|
|Shingles||$100 per square foot.|
|Siding||No more than approximately ?100 depending on size of hole.|
|Caulking||$5 to seal around unit.|
|Roof mounted vents||Approximately $50|
|Gable mounted vents||Approximately $10 to $60|
|Humidistat & thermostat||$50 This price is for a separate controller. Often the powered attic fan will come with one already installed. A whole house fan will not usually include a thermostat and will need a manual switch installed separately.|
Although there may be plenty of contractors out there who say they can fit an attic fan, or you might even think that you can do the job yourself, don’t do it.
Take this advice, only someone trained properly will be able to do the correct calculations to be able to estimate the size of the required fan and the amount of ventilation it needs. If you don’t go down this route, you may find that all sorts of problems will occur such as carbon monoxide buildup near gas-fired appliances, condensation, damp problems and excessive air-conditioning costs. The only person who is properly qualified to do these calculations is a licensed and insured HVAC technician or a company that specializes in fan installation. You will also need a fully qualified professional to cut through your roof or gable wall and ceiling as you must have all joints airtight to prevent a ventilation short circuit. Don’t take any shortcuts.
When you are searching for a suitable company to come and do the work consider the following steps to ensure you find a fully qualified professional.
Due diligence. If you don’t know what this means, how about ‘Do your homework’? Go to the building control authorities in your area, tell them what you intend to do and find out which contractor you need to do each aspect of the work and whether they have to be licensed. You may need to get a permit for certain types of construction work and this office is the place to find out about permits as well.
A list is always a good idea! Before you decide to speak to a contractor or company, make a list of your requirements and what you have already found out from the permit office. It makes the person on the other end of the phone think you might know a little bit about the job. There will be less chance of being conned. Make a second list with all the contact details of prospective contractors and ventilation companies. Check they are licensed and insured and that they do your kind of work. It is no good putting someone on the list that specializes in air conditioning units, is it? Finally make a list of different questions you intend asking the company about, such as:
See what you are getting for your money. After you have received all the quotations, inspect them. The quotation should include a list of all work to be done as well as the name and specification of the fan and any ancillary equipment needed. It should also say whether the company is doing all the work themselves (with fully licensed professionals) or whether they intend using supplied contractors (fully licensed and insured) or whether they expect you to organize the other contractors. If it is possible then ask the main contractor to organize everything for you. It will be easier in the long term as you won’t have to worry about coordinating different trades on different days.
Compare all the quotations and packages and see which is the best value for money. Be aware that the cheapest is not always the best value. Look at the whole package. Here is a more comprehensive list of questions to ask and things to notice, but I am sure you can think of some more:
Check they are who they say they are. Confirm to your satisfaction that all the professionals are fully licensed and insured and have experience in fitting attic fans. See if the company is a member of a professional association and whether their technicians are certified by the North American Technician Excellence (NATE) and partnered with Energy Star. If you do not live in the USA then obviously you will have to find out who the equivalent associations are in your country.
As mentioned earlier, fitting attic fans are not really something for the DIY practitioner to try. There are just too many specialist calculations to cover.
There are, however a few things you can do yourself to help make the fan installation run as smoothly as possible and to make sure the fan will run as efficiently as possible.
✓ Make sure you inspect the ceiling that separates the attic from the living space for gaps and cracks and caulk them all to prevent air leakage into the roof space.
✓ Consider having the access hatch changed for a tight fitting hinged model that will make the roofspace more airtight.
✓ Check you have a spare port in the electrical distribution board (where the circuit breakers or circuit fuses are) to which the electrician can wire the fan. If you haven’t then employ an electrician to fit one.
✓ Decide where you want the main switch to be situated. It would be better to have it located in a communal area rather than in someone’s bedroom.
✓ Have a good idea why you want to have a fan and which kind you think would be best for your purposes.
✓ Clear out a lot of the stored stuff in your attic. Not only is it good to have a clear out now and again but also it will make it easier for the fan installer to work in the roofspace.
✓ Before you sign on the dotted line, make sure you actually need a fan fitted. There may be a better and less expensive way to achieve the same goals. Consult an independent specialist to find out.
✓ Know how much money you can easily afford to spend on the work. There may be cheaper ways to achieve the same goals or you may have to choose a cheaper fan.
If you want to provide additional methods to cool your house or roof space, or if you want to reduce the chances of condensation within your roof space, consider whether it is a good idea to have a powered attic fan or a whole house fan fitted. Both types have their advantages and disadvantages which must be looked at critically before a decision is made. It would be advantageous to consult an independent HVAC professional to find out whether your house would benefit from having a fan installed in the attic and which one. You may even find that something as simple as increasing the thickness of insulation and providing more natural ventilation in your roof space will give you the same benefits as an attic fan.
We hope you have learned something new from my article today, if not then I hope I have jogged your memory on a few key ideas which will prove useful.
Thank you for reading.