Whole House Fan Tips

Whole house fans are really fantastic devices. They can, in many instances, provide extremely effective cooling with very little energy. Only areas with oppressive humidity levels find these fans not so useful. The effectiveness of a whole house fan is directly related to the relative humidity.

I explain in this linked air conditioning article, the effects of humidity and cooling. Simply put, our bodies cool themselves by evaporation. The process of evaporation actually extracts heat from our body. That is why we perspire when we are hot. The body wants that perspiration to evaporate so that it will become cooler. If it is humid outside, the perspiration can't readily evaporate into the air. The air has just about as much water as it wants! That's why it's humid!!!!!!

Air movement increases the rate of evaporation. That is why clothes dry faster on a windy day. Whole house fans are designed for just that purpose. They create a breeze which blows across our skin, which evaporates perspiration, which makes us feel cooler. It's really amazing when you think about it.

Sizing

As with anything, make sure that you have the right size. Can you imagine a large dump truck being powered by a lawn mower engine??? Don't make a similar mistake with a whole house fan. These fans all have different capacities. They can push only so much air. Assuming that you have 8 foot ceilings, determine the total square footage of your house. Multiply this number by 3. The result is the minimum cubic feet per minute capacity that the fan must produce.

Exhaust

What ever goes in must come out. If the fan wants to push 8,000 CFM, it better have a place to easily push it to. Your attic or roof vents must be adequate, otherwise the fan will be restricted. The blade will spin, but it won't be pushing as much air as it should be. You must have 1 square foot of free open exhaust area for every 750 CFM capacity of the fan.

Supply Air

The fan must be able to easily replace the air it is pushing. That means that you must open enough windows and/or doors to give it an ample supply of air.

Balancing Air Flow

Your personal level of comfort is a function of the rate of evaporation. You can maximize this by increasing the rate of air flow through the rooms you occupy during the day and night. For example, at night, you should only have windows open in the bedrooms and hallways feeding these rooms. This will maximize air flow through those rooms. The fan will not suck air from the other unoccupied rooms. During waking hours, reverse this scenario. Close the bedroom windows and open the living, kitchen, family room, etc. windows instead. After all, these are the rooms you have now decided to occupy.

The other rooms will become stuffy. However, these fans are so powerful, that if you had only one window open in the house, it might replace the air in that room with cooler outside air in as little as 15 seconds!

Installation

If you decide to install one of these fans - and I might add that it is a good idea - you must follow the instructions to the letter! One of the most critical steps is making sure that the hole you cut in the ceiling is square! If the hole is not square, the louver will quite possibly bind. That is a major problem!!! Checking the hole for square is simple. Let's say, for example, that the fan needs a hole 31 inches by 31 inches. The hole will be considered square if the two diagonals are the same measurement. A diagonal is the line which goes from one corner to the opposite corner. There are two diagonals in every square or rectangle. In this example, the diagonals would measure 3 feet 7 and 27/32 inches.

Also, if you have to cut ceiling joists, etc., DON'T do it unless you know for a fact that you are not harming the structural integrity of your house. If in doubt, contact an experienced carpenter or a structural engineer. Absolutely do not cut a prefabricated truss!!! If you must, contact a registered structural engineer and obtain his or her opinion. Trusses are not designed to be cut!!!!!

Cleaning

Regularly clean the fan blades and motor. These will get dusty in a hurry. Excessive dust buildup on the motor can lead to overheating which will shorten its life. Be sure that the power supply (circuit breaker) is OFF. These fans are extremely dangerous!! They can cut off fingers or hands. They spin rapidly and, because of their size, they have tremendous tip speeds. The outer tips or edges of the blades are spinning extremely fast. Don't take a chance. Someone may accidentally turn the fan on, a child may do it, anyone. ABSOLUTELY KILL THE POWER!!!!!!

Covers

If you live in a cold climate, you will not use the fan in the winter. The louvers don't always fit tightly. They can leak tremendous quantities of air. The best way to cope with this is to put a lid on the fan. I usually did this fairly easily. I always made a box that fit around the fan. I would usually make this box about 16 to 18 inches tall. This box would keep the attic insulation away from the fan blades. I would then make a simple lid for the box. This lid should have insulation stapled to the top of it.

Timers

Timers are a must. Many people like using these fans at night. However, if the fan runs all night, it can, in some cases, actually get cold in the house. A timer takes care of this problem. You can set the timer to operate the fan for several hours. The fan turns off while you are asleep (ZZZZZZZ).

Variable Speed Fans

Some fans are available with variable speed motors. This can be a benefit. If you need rapid cooling, turn the fan on high. Once you are comfortable, adjust the fan speed so as to maintain your level of comfort. Give these fans serious consideration.

Maintenance

Many fans have rubberized drive belts. The adjustment of these belts is critical. If the belt becomes loose, the fan may not spin fast enough. The instructions which come with the fan usually tell you how to check this adjustment. Keep this booklet. Put it in a zip-lock freezer bag. Attach this bag to the outside of the wood tunnel in the attic. It surely won't get lost if you do this.

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Following is a list of major manufacturers of whole house fans. I personally called many of these manufacturers. Those I spoke with said that they would gladly mail to you, free of charge, their product literature. Many of them will also tell you the location of their closest distributor. I encourage you to call as many as you have time. Ask for the literature and read and compare the qualities of one fan over another.

Ask questions concerning motor maintenance. Does the motor require periodic lubrication, or does it have lifetime lubrication from the factory? Ask for information regarding sizing of the fan. Make sure that you purchase the right size!!! Ask about variable speed fans. Ask about timers. Some fans come equipped with timers. Other fans offer it as an option. Timers are wonderful. Go here for additional information on timers. Here's the list of manufacturers. Please give them a call! Seriously, they love to hear from people like you and me.

• Air Vent, Inc.
• AirScape
  
• Invisco
  
• Ventamatic, Ltd.
• FanAm, Inc.
• Tamarack Technologies, Inc.
  Tamarack makes the HV1000 fan. This one pushes 1,000 CFM and has insulated doors.

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Bathroom - Kitchen Exhaust Fan Manufacturers

Check out the web sites of these manufacturers. Some have great tip sheets concerning bath and kitchen ventilation. Remember to pay close attention to the CFM rating and static pressure. If for some reason, you cannot find the static pressure rating, call the manufacturer and ask for the engineering department. I know that this is extra work, but you will be rewarded with the answer you are looking for.

Broan Manufacturing Company Fantech Nutone Tamarack Technologies Therma-Stor Products

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Installation Tips

I know this sounds crazy, but be sure to carefully follow the instructions that come with your fan. The single biggest reason for problems with exhaust fan installations is failure to follow directions. It only takes five to 10 minutes to read instructions.

Be sure to use the recommended ductwork. Don't mix and match sizes, as you will affect the static pressure load on the fan!

For kitchen exhaust fans, be sure to use metal ductwork! Tape all joints with high quality duct tape. Fires are a real possibility.

Try to locate fans so that the duct run is as straight and short as possible. Remember, a 90 degree bend or elbow is often equivalent to 10 linear feet of duct run. Most fans have a limit to the total length of duct. Pay attention to this number!

Each exhaust fan has a discharge port where the exhaust air leaves the fan. This discharge port may be three, four, five or six inches in diameter. Do not, on your own accord, reduce the size of the duct between this port and your exterior termination cap.

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I have found that it is often best to vent fans and dryers through the roof. I urge you to watch this video of mine to see how easy it is to install the correct vent-cap flashing on a roof. Have no fear - if done right you will have no leaks.

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Posted in Kitchen, Ventilation | 6 Comments

I remember my old home quite well. It was a frame house built in the early 1900's. The windows were original wood double hungs with no weatherstripping. It had an uneven stone foundation with no sill sealer (Sill sealers are foam products used at the transition point between masonry foundations and wood framing systems. They stop air leaks.) In other words, there were massive air leaks into and out of my old home.

The funny thing about air leaks (really it's not so funny) is they are two way. If you feel a cold blast of air leaking around a window, door, baseboard, etc., there is an equal amount of heated air escaping to the outside. If this didn't happen, your house would blow up like a balloon.

Temperature is Everything

This exchange of air in the winter months can cause humidity problems inside houses. How, might you ask?

As air gets colder, it becomes denser. The molecules of oxygen, nitrogen and other gases get squeezed closer together. There is less room available for other things such as water vapor.

I know, I know what you're saying, "But Tim, the weatherperson says that the relative humidity is 60 percent or higher on an almost daily basis. In the summertime, this humidity level is very uncomfortable." Hey, you said the key word.......relative!

Weatherpeople measure humidity as it relates to temperature. For example, let's say it is 20 degrees F outside and the relative humidity is measured at 60 percent. If you were to "capture" say 10 cubic feet of this outside air, and then simply raise its temperature to 72 degrees F, the relative humidity of this same air would drop to around 8 percent! That is really dry.

Static Zots = Energy Loss

Normal daily activities release large volumes of water into the air inside our houses. If you shower, wash clothes or dishes, hang clothes in the basement (now that's a good idea!) to dry, etc., you release water into the air. In fact the air you exhale from your lungs humidifies the air (not to mention your perspiration.) Anyway, people who live in newer, well-built, air tight homes have noticed that they rarely, if ever, get zotted by static electricity. This is so even if they do not have humidifiers connected to their heating systems.

This lack of static electricity means that the humidity level inside their houses is higher, more comfortable. It also means that this humid air is not being diluted by drier, outside air. This means there are fewer air leaks. Want higher indoor humidity and lower fuel bills? Start by finding and fixing air leaks!

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Humidifier Manufacturers

The following manufacturers make humidifiers. Some of these companies have very unusual names. You would never think that they make humidifiers. I suggest that you call them and ask for free descriptive product literature. Not only will they oblige you, they will probably tell you the location of the nearest distributor. Be sure to ask tough questions about how easy it is to change the filter pads. My humidifiers are tough to work on. You have to take the whole thing apart to get to the filter pad. My manufacturer has since corrected this problem. However, I'm stuck with the older models.

Aprilaire Bryant Heating & Cooling Systems Carrier Corporation Lennox Industries NORTEC Industries

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The following indoor relative humidity settings should provide you with a good comfort level. Almost all humidifiers come equipped with a humidistat. This device works just like your thermostat. You set the humidistat to a desired humidity level. When the humidity reaches that point, the humidifier stops working.

Suggested Indoor Humidity Settings

Outside Temperature	-10 F	0 F	10 F	20 F	30 F
Recommended Indoor Relative Humidity	20%	25%	30%	35%	35%

The following table gives you an idea of just how "dry" outside air is when it is brought indoors and then heated to room temperature. If you have low humidity in your home, you have air leaks. The dry outside air is mixing with your humid air and lowering the overall humidity. Plug your air leaks and you may not need a humidifier.

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