I recently put a floor down in my attic, and am concerned that the now-accessible attic fan will chop someone’s fingers off, so I’d like to screen it off. My question is whether having a screen in front of a fan makes the fan less efficient.
I would put up the screen in any event, but would spend more time picking out a less obstructive one if it makes a difference. If not I’ll just cut a chunk of window screen from a roll that I have in the basement.
On the subject of attics, I also have a question about attic insulation. In the winter I put one of these insulators over the opening in the attic floor (it’s a big bathtub-shaped piece of Styrofoam). My question is, if heat rises, does this mean that there is no value of putting it there in the summer? Because if heat from the attic had no impact on the house below, then what’s the purpose of having an attic fan to begin with?
Not a big deal, but easier to put it out of the way somewhere than to have to move it every time you go up.
Yes, screens can and will disrupt the air flow. The severity of the impact depends on how dense the screen is and a number of other factors that are probably too nitpicky for anyone but an engineer to get into.
Screen your fan. The screen will cut down airflow but not enough to be a problem. That said, ours is screened with expanded metal. I wouldn’t trust window screen to hold if someone had a mis-step.
We don’t insulate the fan in the summer; we’re using it. What will help is some good thermostatically-controlled roof vents, to vent the heat out of your attic so it won’t tranfer back into the living space.
Yes, it will increase the resistance to flow and make the fan less efficient. How much so is hard to say without knowing the fan or screen specs, but for something as fine-mesh as a window screen, maybe a couple inches of water pressure drop. As to whether it makes a difference, that depends. Some attic fans are very cheap items and run quite hot - you might want to try to judge how good of a fan you have before you restrict the flow too much. My attic fan has large warnings about not restricting the flow because it could cause overheating.
If the point is to prevent fingers from being chopped off, quarter-inch “hardware cloth” should screen it just fine. With quarter-inch gaps in the mesh, I can’t imagine that it would have a significant impact on airflow for your purposes.
As for insulation: house fans work not only by cooling the attic, but by drawing cooler air inside from around the house. Having shade plants or a porch around the house may help. Also, I tend to keep my house closed up until after the peak heat of the day has passed, then I open all the lower windows and crank up the attic fan. I leave the windows open all night, then close them in the morning to trap the cool air in.
Don’t have a cite handy for this buuut, I’ve read that “standard” window screen reduces airflow by ~25%.
More importantly, and this goes to Una’s point about some fans running hot, window screen does a great job of collecting amazing amounts of dust, pet hair, etc and adds fuel to the fire hazard. Think dryer lint, one spark and it’s smoldering!
Even if the screen itself doesn’t really impact the airflow once it’s clogged with dust it will, and it’s a bitch to keep clean.
¼" or even ½" hardware cloth should be more than sufficient to keep your fingers safe.