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.
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DEAR TIM: Is there special type of installation required when installing a window box or garden box? Is flashing required to be installed over the limestone sill? Is other flashing required around other parts of the window? Thanks, Dan N., Deerfield, Illinois.
DEAR DAN: The installation of window boxes is a function of their design. Some window boxes are made to rest on platforms while others have a special lip that allows the window box to hang from special stainless-steel clips. I prefer the fiberglass window boxes that use this special clip system.
You do not need flashing if you keep the window box away from the side of the house ever so slightly. Water problems happen when you install a window box against the side of a house so no air can get between the box and the side wall of the house.
Dear Tim: I have some 4x8 sheets of 7/16" OSB that I have been storing pending the construction of a private 10'x20' storage shed. The OSB got wet and appears to be waterlogged. It is holding together though quite well, and not breaking up. Will it be usable as sheathing for wall and roof construction and will it dry out? Thanks, Dean.
Dear Dean: The OSB board will indeed be fine if you are sure that it is not falling apart. It is actually made with special glues that can get wet repeatedly. I suggest you let them dry in a shaded area, not in direct sunlight, and do so as soon as possible.
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.
Overdoing it - Too Much Humidity Creates Problems
I have a humidifier attached to my forced air heating system. It is a neat device. Many people have them. Every time the furnace turns on, a little electronic switch opens a small water valve. Water flows over a pad through which air flows. The water evaporates from this pad into the air. BINGO! The humidity starts to rise inside your home.
Well, sometimes - and this has happened to me - you can get too much humidity. I have gone to bed with everything just fine. The furnace was humming and the humidifier working just fine. I wake up and it looks like someone turned on a lawn sprinkler inside my house near every window. Water is running down the windows and pooling on the floor! I usually run around cleaning up saying, "We've had a major malfunction. All engineering personnel report to the quarter deck immediately!"
The cause of the problem is easy to identify. Two things possibly occurred at the same time: the inside relative humidity was climbing and/or the outdoor temperature level dropped. Usually it is the outside temperature drop that causes the problem. The inside temperature of the window glass drops as the outside temperature drops. The water vapor in the air begins to condense as the temperature of the glass drops.
Hidden Problems
If you have had water condense on your windows like me, you may have had more serious problems. There is a good chance that water condensed on hidden, cold wall or attic spaces. Remember earlier we talked about air leaking into and out of your house? Well, those places where it is leaking out may be saturated with water. Recently I had a caller to my radio show tell me about basement fiberglass insulation that was saturated with water. The insulation was up against the band board (rim joist) just above the foundation. This framing lumber has a direct connection to the cold siding outside.
It transmits this cold into the basement. Just like a cold can of soda or beer begins to sweat in the summer humidity, so will this rim joist inside. But, what happens if this is going on inside the walls of your house where you can't see? How about your attic? These are all possibilities. Wood rot, mildew, etc. can become a real threat.
Maintaining a Balance
If you have a humidifier, or plan to purchase one, you need to pay attention to outdoor weather. If the temperature is forecast to drop over a period of hours, you may wish to turn down or limit the amount of humidity you are introducing into your air.
Many manufacturers recommend that you adjust your humidifier to a setting just before any fog would appear at the edges of a window. Remember, this fog will appear at different outdoor temperatures and different indoor relative humidities. It is not easy to do! There is no one setting that will work for all outdoor temperatures. Plus, if you have a programmable indoor furnace thermostat the problem gets worse! At night, you probably have the thermostat set itself back 5 to 7 degrees. Well guess what? This will cause the indoor relative humidity to rise in and of itself with no adjustment at all to your humidifier. Maintaining proper indoor humidity is not easy.
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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.
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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
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Outside Temperature
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-10 F
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0 F
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10 F
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20 F
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30 F
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Recommended Indoor
Relative Humidity |
20%
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25%
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30%
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35%
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35%
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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.
| Outside Temperature | Outside Relative Humidity | Indoor Humidity when air is heated to 72 degrees F |
| -10 degrees F | 40% | 1% |
| 60% | 2% | |
| 80% | 2% | |
| 0 degrees F | 40% | 2% |
| 60% | 2% | |
| 80% | 5% | |
| 10 degrees F | 40% | 4% |
| 60% | 5% | |
| 80% | 7% | |
| 20 degrees F | 40% | 6% |
| 60% | 8% | |
| 80% | 11% | |
| 30 degrees F | 40% | 8% |
| 60% | 13% | |
| 80% | 17% |
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Can you imagine the mess I once came upon when I entered a basement where the dryer had been venting inside for about eight years? There was lint everywhere! It was a huge mess, not to mention an incredible fire hazard. Cotton fibers were everywhere.
The vent had come unhooked from the bottom of the dryer and the homeowner didn't have a clue. They thought the stuff was cobwebs. It was believable as the accumulation was slow and they had grown accustomed to its presence. It freaked me out.
Basement Venting - Easy!
Getting dryer exhaust from a basement is a piece of cake. It usually involves two 90 degree bends and sometimes three. Often there is only 10 to 15 feet of pipe. Many people go the easy route and choose the plastic flexible variety. This tubing does not comply with current code standards. I have always been a smooth metal pipe man myself. It is easy to work with and fits together in a flash. Cutting it with tin snips is also a cinch.
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.
The Vent Cap
Many people are familiar with the wall vent terminal for dryer vents. The inexpensive ones only have an opening that is about 2.5 or 3 inches big at its widest point. These are loser dryer vents. Try to locate those that have a 4 inch opening or use the ones that have the mini-louver doors. These types offer the least air flow resistance.
The wall dryer vents can't be used on a roof location. You must get a roof vent cap that is designed to shed rain water. These vent caps also have great built-in flashings. The best part is that they are inexpensive.
Venting Through a Roof
I have installed quite a few dryers in second and third story rooms. The people always wanted me to vent the dryers through the roof once I gave them the option. It is a little more work but it is not terribly difficult. It is no more work than installing a plumbing vent pipe. The key is to locate it in such a way as it is least visible from the ground. You don't want lint fibers up on the roof to greet your visitors, do you?
Clamps and Tape, Not Screws
When installing pipe between the dryer and the vent cap, use the special large clamps that secure the pipe to the fittings. If you screw metal pipe together, the screws can catch lint over a period of time and actually cause problems.
The seam between metal pipe and fittings should be taped with the foil faced duct tape. This is REAL duct tape, not the imitation stuff you think is duct tape!
You buy foil faced duct tape at HVAC wholesale distributors or places where metal ductwork is sold. It really sticks to metal pipe and the tape is often reinforced. It is the most wonderful tape I have ever used for securing metal pipe. It makes off-the-shelf imitation duct tape look sick.
Insulate the Pipe
If you decide to vent your dryer through the roof, you absolutely must insulate the section of metal pipe that is in a hidden spot where cold temperatures can surround it. Failure to do this will lead to massive condensation and leak problems. If you live in a warm climate, you don't have to insulate the pipe at all.
Be sure to wrap the pipe with at least three inches of fiberglass insulation from where it penetrates the ceiling below all the way up to the underside of the roof. Use the wonderful foil duct tape to secure the insulation and tape the seams completely.
Hanging Pipe
The best way to hang horizontal runs of dryer vent pipe is to use the plastic J hooks designed for four inch smooth, rigid metal pipe. These heavy duty hooks have prepunched holes that allow you to quickly attach them to wood floor joists or any surface that will accept a nail or screw. They are simply the best!
Different Pipes
I have had to use four inch rigid metal pipe on occasion to vent dryers through roofs. I chose this pipe because I could get it in long lengths without a seam. I was able to insert it through a roof hole all the way down to the second floor dryer location.
This type of pipe has a very smooth interior surface that offers minimal resistance to air flow. It is also corrosion resistant.
Current code calls for a smooth, rigid metal dryer duct of at least 4 inches and no longer than 25 feet. Be sure to check your local codes for any additional requirements or restrictions.
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Clothes Dryer Vent Tables
Properly connecting a dryer to an outside vent terminal is not as simple as it might seem. You need to be concerned with the total length of run of the pipe, the type of pipe you use, how many bends are in the pipe, and the design/shape of vent terminal at the end of the pipe.
The dryer blower only produces so much energy. This energy is offset by friction within the vent pipe. This is why you must be concerned with the total length of the pipe. Ninety degree angles also create friction. Each bend equals the friction the air would encounter if it ran through an additional 10 feet of straight pipe. Smooth metal pipe offers less friction than flexible pipe with lots of little ridges within the pipe. The vent cover shape and design is important as it also acts as a partial dam or blockage to the exiting air. A vent with a wide mouth opening say four inches or so or one with the little louver doors that swing wide open offer the least resistance. The smaller the vent opening the greater the amount of final resistance.
Use the tables below to calculate how far your vent can be from the dryer. Pay attention to the type of pipe you have and the vent configuration!
Vent cap with wide four inch opening or mini-louvers and smooth metal pipe
Vent cap with narrow 2.5 inch opening and smooth metal pipe
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Vent cap with wide four inch opening or mini-louvers and flexible ribbed pipe
Vent cap with narrow 2.5 inch opening and flexible ribbed pipe
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