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autojoe
bathroom exhaust fan venting

Installing exhaust fan.contractors previously had used a flexible plastic non insulated duct which filled with water.it was vented through the side wall 5 foot away.I live in a cold climate in pa.cold winters.The calculated cfm was 47 and had a 50 cfm fan installed.I bought a 80 cfm fan.Heres my question....I planned venting through sidewall like before and bought r-8 insulated flexible duct.Is this acceptable?if yes do I install a elbow to bring up from fan then connect the insulated duct to elbow and insulate elbow or just hook insulated duct to fan and bring up on top of ceiling joists and over to sidewall and connect to outside?also do I use a wire tie or pipe clamp ect to attach the flexible insulated duct to the fan and to the outside vent and wrap with foil tape or just use foil tape?If insulatede duct is not acceptable what is the best way?Thanks in advance.

dj1
Re: bathroom exhaust fan venting

The code says:

"The total horizontal run of a vent must not be greater than 75% of the vertical height of the vent"

If your old vent ran 5 feet horizontally, and your vent height was less than 7'6", then it was not to code. If that is the case, this is probably the reason why it failed.

My suggestion:

Measure the height of your vent. If it's less than 7'6" look at venting it through the roof, not from the side.

As far as insulating the duct: I am not familiar with PA codes, so I can't comment on this.

To hold vents in place, use straps that hang on rafters.

Connections can be wrapped with duct tape or foil tape.

Nestor
Re: bathroom exhaust fan venting

Autojoe:

"contractors previously had used a flexible plastic non insulated duct which filled with water. it was vented through the side wall 5 foot away."

If this was in an unheated portion of your home or home's attic, they shoulda known that was gonna be a problem.

"I planned venting through sidewall like before and bought r-8 insulated flexible duct.Is this acceptable?"

If it's intended for use on bathroom fans, then that would solve the condensation problem. The only thing is that if you can keep the duct as short and straight as possible, you get the most air movement through it, and that means that the fan works more efficiently. Generally, flexible ducts offer much more resistance to air movement than rigid galvanized or aluminum ducts, and that's because of the undulations on the surface of flexible ducts compared to the smooth straight interiors of rigid ducts.

"if yes do I install a elbow to bring up from fan then connect the insulated duct to elbow and insulate elbow or just hook insulated duct to fan and bring up on top of ceiling joists and over to sidewall and connect to outside?"

I'd just go with the largest radius curvature you can while keeping overall length of duct to a minimum. Whenever you put a bend in a flexible duct or elbow in a rigid duct, you increase the resistance to air flow. However, the larger the radius of curvature, the less the air flow is impeded, so using two 45 degree elbows on rigid ducting is preferable to one 90 degree elbow. So, route your ducting knowing that the more bends and the sharper the bends the greater the resistance to air flow, and the longer the distance the air has to flow, the greater the resistance to air flow. It's pretty much an art after that. Alternatively, if a larger duct will fit, maybe phone up the company that made your flexible insulated duct and see if they make the same thing in larger diameter ducting (say, 4 inch for clothes dryers and 6 or even 8 inch for forced air ventilation systems). That way, you can compensate for the higher air flow resistance offered by flexible ducting by having larger ducting.

"also do I use a wire tie or pipe clamp ect to attach the flexible insulated duct to the fan and to the outside vent and wrap with foil tape or just use foil tape?"

I'd slide the insulated flexible duct as far onto the vent on the exterior wall as possible, and use nylon cable ties to fasten it in place. If this proves to be difficult, buy some 99.9% glycerine at your local drug store and lubricate both the ID of the insulated flexible duct and the OD of the piece it slides over to allow you to slide the insulated duct on further. Glycerine behaves very much like a light oil to reduce friction, but evaporates completely without leaving any residue so it's ideal for situations like this where you want to reduce friction but don't want any oil residue remaining behind afterward for dust to stick to.

(Also, to my knowledge, if you're using rigid galvanized or aluminum venting on a bathroom fan you can also use screws. However, screws of any kind cannot be used on the ducting from electric clothes dryers because lint accumulates on the screws and could potentially result in a lint fire inside the dryer's duct.)

PS:
you might be interested in opting for a larger diameter rigid duct...

If you go to a larger duct size, then you will need reducers at both ends of that larger duct to connect to the 3 or 4 inch fan and the 3 or 4 inch vent on the exterior wall. To get insulation for larger RIGID duct sizes, phone around to the heating contractors in your area to find out who in town sells pipe insulation (most commonly called "ASJ", or "All Service Jacket").

ASJ is a fiberglass pipe insulation that comes in a bewildering variety of pipe sizes and insulation thicknesses. It's not very expensive, so it's feasible to use as bathroom ceiling fan duct insulation, but I'd think it would only work well on rigid ducts like galvanized or aluminum.

Regarding the elbow(s), the same places that sell ASJ will also sell fiberglass batt insulation in rolls 6 inches wide and 1 inch thick that can be used to insulate around complicated shapes that don't lend themselves to insulating with ASJ. You can wrap that batt insulation around any elbows you install. Alternatively, you can cut two pieces of ASJ at a 45 degree angle with a hand saw and fit them around any elbows in your ducting as well.

Finally, if you invest in an inexpensive tool called a pipe shooter:

and mount that pipe shooter in an electric or cordless drill, with a tape measure and a little patience, you can fit ASJ snuggly around almost anything.

I'd insulate around the fan housing itself as well.

autojoe
Re: bathroom exhaust fan venting

thanks for all replys.....I am going to use solid galvanized duct 4 inch and remove the flexible duct from the insulated r8 duct and then wrap that over the solid duct and tape all joints with foil tape.is 1/2 inch per foot slope towards outside good enough?The distance from the vent to outside wall is 3 feet 2 inches.Thanks again.

canuk
Re: bathroom exhaust fan venting
autojoe wrote:

thanks for all replys.....I am going to use solid galvanized duct 4 inch and remove the flexible duct from the insulated r8 duct and then wrap that over the solid duct and tape all joints with foil tape.is 1/2 inch per foot slope towards outside good enough?The distance from the vent to outside wall is 3 feet 2 inches.Thanks again.

Sounds about perfect.
Just remember to have that slope toward to exterior vent cap.

dj1
Re: bathroom exhaust fan venting

Looks like you will be doing a professional job.

Don't forget the hangers.

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