Attic fan and venting

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Old 10-09-16, 06:10 PM
W
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Attic fan and venting

Hi All, Question here is concerning our attic fan. This is not an attic fan that is located in the attic to vent it, this is the type of fan that is located in the ceiling of our home that we can turn on to bring in outside air through the windows. We found out the hard way what happens when one uses this type of fan if your basement toilet trap runs dry from non-use...."PEWEYYY"...LOL. But now I just by luck was taking a look at our water heater and noticed that when it is cycling and we have the attic fan running that the water heater does not vent....the vent pipe was not even warm. After I figured out that this may be the problem I immediately went up and shut the attic fan off and withing the 2 minutes it took me to get back to the water heater the vent pipe was hotter then heck...the way its spose to be. So I guess for the past 20+ years that we have been living here that every time we ran the attic fan and the water heater was running that we could have/probably were getting C/M fumes into our home. Anyway, sorry for the winded run down, but what is the fix for this.....or is there one other than getting rid of the attic fan ?? Suggestions would be appreciated. Thanks
 
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Old 10-09-16, 06:42 PM
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Hi windy,
You are lucky that you discovered the problem before it got a lot worse. I'm a retired energy auditor and what you are dealing with is something we test for in every home we visit. It is called a CAZ test, (combustion appliance zone). It ca occur in any home when air sealing tightens up the house or when you own a whole house fan of huge range hood. If you have a gas furnace it may be having the same problem, although the heating season is not exactly when you use the big fan.

The solution would be to either eliminate the big fan or convert all combustion appliances (furnace and water heater primarily) to sealed combustion. An electric water heater would also work.

Our CAZ test goes beyond just the big fan as we turn on all exhaust sources to be sure the water heater can establish and maintain a proper draft.

As a note, Google the symptoms of low level CO exposure. High levels can be fatal, but low levels can also cause a variety of health issues.

What other combustion appliances do you have?

Bud
 
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Old 10-10-16, 08:57 AM
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Thank You for the reply. What you mention seems to be spot on and it is appreciated and noted. The only other gas appliance is the furnace along with a gas range, but there is no hood for that. I can only assume (accurately or not) that since the only time we run the attic fan is when the windows are open that any or most C/M gases are also being sucked out of the home while it is running. All except of course the C/M that may not make it out of the house during the short amount of time between when the fan is shut off and the windows are closed. Hopefully this is minute !!! We can also only hope that since the only time this phenomenon happens is when both the fan and water heater are running (matter of chance) that there has not been any heath issues related. When you mention "sealed combustion", Does this mean the entire unit must be sealed.....or just the venting pipes/flumes themselves ?
 
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Old 10-10-16, 09:35 AM
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The sealed combustion units have both an intake and exhaust pipe, often pvc. You see them often with new furnace installations. Existing units cannot be upgraded to the sealed performance. I believe naturally vented water heaters are no longer available??

The tough part is, when all is working right there is little to no CO but the danger is still there. Consider the number of gas ranges that have no direct vent. They are however now advising a hood vented to the outside and running anytime the burners are on. Part of that deals with the newer tighter energy efficient homes, but it is not something where you want to rely on operator diligence, meaning not running the fan when the windows are closed. A common failure occurs when it gets cold and someone closes the windows but forgets to turn off the fan.

A whole house fan is combining two functions, draw in cool outside air and purge the attic of the heat built up over the heat of the day. If you use a window fan to blow air "in" it pressurizes the house and there is no risk of backdrafting. Then, install an attic exhaust fan if purging the attic heat is still desirable. In most cases good attic ventilation, air sealing house to attic, and lots of insulation works sufficiently. The fan approach is a quick fix and not the best choice, as you have discovered.

Bud
 
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