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Old 09-13-2011, 10:04 PM   #1
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attic venting


Since installing a high eff. furnace, I get ice on the attic ceiling in very cold weather where the interior bath fans exit into a roof vent, not thru the roof. Icicles form and then melt when the sun comes out, causing ceiling leaks in the bathrooms and wet insulation. How do I resolve this problem. Thanks, Andy

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Old 09-13-2011, 11:06 PM   #2
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Since installing a high eff. furnace, I get ice on the attic ceiling in very cold weather where the interior bath fans exit into a roof vent, not thru the roof. Icicles form and then melt when the sun comes out, causing ceiling leaks in the bathrooms and wet insulation. How do I resolve this problem. Thanks, Andy
They exit into a roof vent but not through the roof? Do you mean that they exit into the attic and not through the roof?

What is the ventilation source for the attic?

Whatever the source or venting, you have too much moisture in the attic and that must be addressed by either more ventilation or less moisture or both.

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Old 09-14-2011, 11:54 AM   #3
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attic venting


Thanks for the reply, The bathroom vent pipes go up into the rood vents, but not thru them, the pipe ends about 1 inch from the roof vent top. There are eight roof vent, about 1 sq. ft each. I had the house for 16 years, never a problem until I installed high eff. furnace that no longer uses the flue vent thru the attic now vents thru the side wall.
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Old 09-14-2011, 03:18 PM   #4
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I would say you have to install vents specifically for the bathroom vents (which is best done through the gable roof ends). The way it is now there is no guarantee the moist air exists the attic.
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Old 09-15-2011, 08:30 AM   #5
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attic venting


They need to vented to outside.
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Old 09-15-2011, 09:57 PM   #6
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A special damper vent, such as one similar to this model by Broan, should be installed.

http://www.iaqsource.com/product_ima...product=172638

Broan Model RVK1A Roof Ducting Kit for 4" Duct
Copyright 2011 | National Trade Supply, LLC | All Rights Reserved


The ducting NEEDS to be TIGHTLY Sealed to the exhaust piping on the interior of the vent product.

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Old 09-15-2011, 11:20 PM   #7
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Be sure to insulate any exhaust ducting from the outside/attic temperature to prevent condensation inside ducting from a hot shower. Try to use straight pipe for ducting rather than flex when making long horizontal runs or vertical runs. The flex, being 4" will help offset the turbulence and pressure loss if exiting the fan at 3". There is twice as much surface area in flex (compared to straight) if not fully stretched, to gather moisture on the inside walls. Insulate the fan housing box and the wiring hole from attic air. Use foil tape and nylon straps (if supplied, as shown) at all connections. Insulate (and support) it well, the pre-made duct/insulation is only R-6-7.

Gary
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Old 09-16-2011, 12:41 AM   #8
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Be sure to insulate any exhaust ducting from the outside/attic temperature to prevent condensation inside ducting from a hot shower. Try to use straight pipe for ducting rather than flex when making long horizontal runs or vertical runs. The flex, being 4" will help offset the turbulence and pressure loss if exiting the fan at 3". There is twice as much surface area in flex (compared to straight) if not fully stretched, to gather moisture on the inside walls. Insulate the fan housing box and the wiring hole from attic air. Use foil tape and nylon straps (if supplied, as shown) at all connections. Insulate (and support) it well, the pre-made duct/insulation is only R-6-7.

Gary

Very good add-on advice Gary.

Thanks for the additional input.

Ed



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