How to ventilate attic bedroom
Our house has a 15ft by 15ft, 3rd floor bedroom under a pyramidal-shaped roof. (Note that the pyramidal roof does not rise to a sharp point, but rather rises short of a point into a 6ft by 6ft square, flat crest which is covered with sheet metal.) Heat rises throughout the house and is trapped in the dead air space under the pyramidal ceiling of this bedroom. In the Summer, it is stiflingly hot! I'd like to install an appropriate exhaust ventilation to draw the heated air out of that bedroom. I am inviting your ideals on how to do this.
I might choose to over-size the system so it can act as a whole house fan to draw hot air from throughout the entire house out through the roof unit. On the other hand, the system should be quiet enough to run in a bedroom and allow people to sleep (we tolerate moderate white noise and would be acceptable to us.)
I'd like advice on what ventilation system I should install. I picture some sort of powered ventilator fan system which penetrates the peak of my roof through the flat 6' by 6' flat crest. The ceiling of the bedroom is directly attached to the rafters of the roof, so that there is roughly a 10-inch thickness between the plaster interior ceiling through to the outside shingles of the roof. Hence, there is no need for long ducts. On the negative side, the fan and motor noise cannot be muffled by use of a long duct passage!
It seems to me I want a ventilator unit in a mushroom shape where the motor and fan are placed up in the mushroom. I assume I should buy a substantial, high-quality unit. For example, I don't want too cheap a unit which might creak from side-to-side motion creaking that might come from an imbalanced fan. Or a sloppy installation which does not properly anchor the unit against vibration. How do I connect the unit to the roof and duct the unit to the room interior? What kind of grill or louvered arrangement should face into the room?
In the Winter, I have the reverse problem! The ventilation unit penetrates the peak of the roof. It will loose house heat via conduction through aluminum housing and convection through leaks our through the vent passage. These are the same problems that plague chimneys. So, I need an insulated unit itself or an insulated door to shut off air and heat flow through the unit in the winter.
And finally, the aluminum ventilator unit will sit at the topmost part of a 3-story house making it an attractive target for lightning. How can I deal with a possible lightning strike to this unit, which might destroy the motor and apply a shock of voltage to the house wiring?
Please give me both general comments on design and function and specific recommendations on particular ventilator products and components.
Re: How to ventilate attic bedroom
George, I saw a similar situation at an octagonal shaped church. At the very top was a cuppola about 8' high and 8' in dia.
The pastor asked the same question..could I install a fan.
I suggested mearly installing a 2' x 4' register and ducting it back to the return air duct with a manual damper to regulate flow.
It could have been "greaner" in the summer by venting outside but worked great year round.
No roof penetration, no lightning hazard, less up-front dollars, no noise, no maintenance, no loss of conditioned air.
Good Luck from Columbiana, Alabama
Maurice Turgeon, http://thesemi-retiredelectrician.com
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