Cutting off or filtering HVAC external air intake due to wildfires

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Old 09-13-20, 03:19 PM
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Exclamation Cutting off or filtering HVAC external air intake due to wildfires

Hi everyone,

I'm in the Pacific NW where there are unprecedented wildfires causing catastrophic air quality. Literally the air quality is off the charts bad.

The temperature has dropped dramatically since there is no sun, so I have turned off the AC. But I have turned on the circulation function.

I have 2 sets of these vents outside my home. My home was built 7 years ago.



I believe one set is intake/exhaust for the circulation system. I could feel exhaust as well as intake (the downward facing pipe was the intake). These are not the kitchen exhaust or dryer exhaust, which are higher up in the wall. EDIT: The set with vigorous intake/exhaust were for the gas water heater. The other set did not have as pronounced intake/exhaust, but still some.

A few questions:
1. To minimize intake of smoky air, can I tape a filter on the intake pipe? Is there any harm if I just duct tape it shut temporarily?

2. Is it better to have the circulation fan run 30% intermittent, or continuous? Those are the two settings aside from off.

3. What's the other set of pipes for? Same function, only during heating? The other set is for the gas tankless water heater. Definitely can't plug that one.

Thanks.
 

Last edited by Waylo; 09-13-20 at 04:03 PM.
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Old 09-13-20, 06:19 PM
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I'd recommend turning off the circulation system at this time.

If you turn the circulation system off there shouldn't be any air exchanging.
You'd need to make sure the system is definitely off before covering the outside vents.

 
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Old 09-13-20, 08:10 PM
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There's actually no setting to turn off the fan circulation on the thermostat. Only ON (full time), CIRC (30%), or AUTO (also 30%). The builder said it's to make sure there's ample... uh, circulation at all times.

Short of cutting the circuit breaker, it will run some.

Looking at the manuals included with the furnace, it looks like those pipes are for the furnace. So if there is an external intake pipe just for the circulating fan, it may be in the attic or elsewhere.
 
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Old 09-14-20, 09:24 PM
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As an update, I killed the furnace power through the circuit breaker and stopped the circulation. The air quality is much improved now!

So I imagine there is some intake pipe somewhere that is not directly outside the utility room. If I access the attic space to go searching right now, that would dump all the polluted air directly into the master bedroom, so that's a project for another day.
 
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Old 09-14-20, 09:38 PM
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You may be right. There may be a "fresh air" in line for the furnace room.
 
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