Mixed exhaust vents: Wind turbines and ridge vent
People who know me hear this often: “Don’t Over-Think It”. Things are usually never as complicated as they seem. Of all the questions I get from customers, Attic Ventilation is probably the most misunderstood, and overcomplicated topic in the home efficiency/improvement area. So hear me now: “DON’T OVER-THINK IT”
Attic ventilation is VERY simple. You have HOLES in the bottom of your attic (usually soffit vents) and HOLES in the top of your attic (ridge vent, wind turbines, static vents or power fans). Ideally, air comes IN the bottom and OUT the top. It’s just like a chimney in your home. Pretty simple. Holes in bottom, holes in top…got it?
Think about this. If I came to your home today and started ripping out your soffits and cutting lots of holes in the top of your roof eventually the air temperature in the attic would get close to whatever the outside (ambient) air temperature is. Air temperatures would drop but surface temperatures would not drop much due to the radiant heat gain. A radiant barrier works together with decent attic ventilation to drop both air temperature and surface temps.
Here is where many people screw up attic ventilation. More is not always better. The thought process goes something like this: “If I add an electric or solar attic fan, or some ridge vents, or a few wind turbines or static vents or maybe ALL OF THEM, I’ll move more air and my attic will be cooler” WRONG!!!!
Dirty or clogged soffit vent
Let me ask you. Have you EVER seen a chimney with a fan sticking out the side in the MIDDLE? Of course not, why? Common sense would say that the fan would pull air from BOTH the top and bottom of the chimney. Your attic is EXACTLY the same. Why on earth put an electric fan 15” away from a ridge vent or wind turbine? Yes, there will be great airflow in the top 2 feet of the attic and the rest of the air will be almost stagnant.
Air always travels the path of least resistance. Mixing exhaust vents is a bad thing. The strongest vent will dominate and the other exhaust vents will probably become INTAKE vents. This short-circuits the whole concept of air coming in the bottom and out the top. This can happen many different ways from actually mixing different types of exhaust vents to having ridge vents on EVERY ridge. Usually the ridge vents about halfway up the roof will become the intake vents and totally short circuit any air coming from the soffit vents. All the exhaust vents should be within a few feet of each other from the top.
How to fix it? Start at the bottom with your soffit vents. Have you EVER cleaned your soffit vents? 95% of homes have clogged, blocked or painted over soffit vents. Or, the holes behind the vents are so small virtually no air is coming into the attic. I’ve even seen million dollar homes where they just screwed in the vents and did not bother to even cut holes. I’ve seen many homes where just cleaning the soffit vents (use a dry nylon car wheel brush) will drop the attic temperature 20º in 20 minutes. And those wind turbines that were “broken” start spinning like crazy. Get it? Air comes in and now air will go out.
Hole cut too small behind soffit vent
Next, pick one type of exhaust vent and go with it. By combining a basic strategy of holes in top and bottom your attic will be cooler in the Summer and drier in the Winter. Remember, keep it simple, and don’t over-think it…Holes in the bottom, holes in the top.
Tags: attic fan, Attic Ventilation, attic wind turbine, ridge vent, soffit vents, solar attic fan
I agree completely!!! Ventilate, ventilate, ventilate! when I crawl up into the attic of an older home, I notice that there is never enough air flow. usually there is one or two roof vents and a very few soffit vents. One of the more successful experiments I have done, is to take an AC booster fan (~25watt) and secure it into the existing roof vents while adding more soffit vents. In the middle of summer, there is a difference between passive and active air flow. I prefer passive, but some homes just need a little extra help. If you figure out the basic air-in, air-out flow, then adding a little fan (with a thermostat) can help get rid of the heat faster than waiting for the heat to rise. I don’t like the huge 175 watt roof fans due to the amount of electricity they use and the fact that you can never get enough air into the attic through the soffits to keep the fans from pulling your good AC from the house into the attic.
I usually stick with my passive vents and occasionally use a booster fan when really needed.
Toff
Okay, after reading this, I’m canceling my ridge vent project. I have four exhaust vents a few feet from the top of my roof and my soffits are not clogged, so I’m fine. I cut holes in the radiant barrier by the exhaust vents just as your website instructed. Thanks for the help.
Kevin in Sugar Land