Positive pressurization

[JackOfDiamonds]

Here in the west the wildfires are intense and I'm suddenly interested in indoor air quality.

Although I have a good furnace filter and I run it 24/7, it can't keep up with the levels of smoke outside, plus I have a suspicion that running the HVAC might actually be sucking in smoke from outside.

We all know that houses aren't hermetically sealed and there's always some drafts. However if the house is positive pressure, even a tiny bit, it will mean air will diffuse outward through the drafts, and smoke won't be able to get in. If you can keep new smoke from coming in, then my furnace filter and room purifiers have a chance of keeping the air inside clean.

Positive pressure is how semiconductor cleanrooms are kept clean. They always keep the cleanroom at a slightly higher pressure than outside, so even if you open doors or whatever, the clean are rushes out instead of dirty air rushing in. I assume they do this by pulling in make-up air from outside and filtering it. So you should be able to duplicate this for a house by rigging up a bathroom exhaust fan, or a range hood, putting a furnace filter or HEPA filter on it, and running it whenever it's smoky outside to pressurize the house. Would this work?

 

[The Cobbler]

I have a suspicion that running the HVAC might actually be sucking in smoke from outside.

unless you have window air conditioners it is not likely. I'm not sure how well a heppa filter would work for smoke . just not something I can comment on.

 

[Kaizen]

The more I think on this the harder it would be to determine. A blower door test would identify leaks and amount of volume. But you really need to have whatever the test is that determines air pressure. Then compare that with the system running and it not running. The smoky air will infiltrate regardless of negative pressure. If both are equal it will flow out and in. If no substantial drop in pressure then air purifiers esp in bedrooms might help.

 

[ericm]

This member's garage thread has a bunch of posts on a filter system for wildfire smoke for an HRV: https://www.garagejournal.com/forum/threads/woodys-works-garage.263351/page-73 That's the carbon filter, the particle filter was earlier.

If your filter media is large enough then the pressure drop will not be too much for the system to handle.

I am planning to get something similar for the house we're getting built in Oregon. It's in an area that has "smoke season" each summer though it's actually pretty variable. The house will be well sealed but the HRV system will be pulling in air from outside. The GC's answer to dealing with smoke is to turn off the HRV system, which I find insufficient. If I can't get the GC and HVAC sub to do what I want I'll have them run the pipes such that I can add the filters myself later.

For an existing house you'll need to find and plug the air leaks, or enough of them to make a difference.

You could add filters to the current HVAC but the ducts are probably marginal as it is and the added resistance from tighter filters will make it worse.

Its not pretty but you can build a Corsi box (box fan with filters around it) to filter the air inside the house. I'm told they work pretty well.

 

[JackOfDiamonds]

My house is 30 years old and shoddily built as all houses of its era and region. Many of the ducts are not even sealed and I can't access all of the ones in the walls or attic to seal them now. That's why I suspect the HVAC system itself may be part of the problem of keeping smoke out.

Pressure inside the house can be measured by a window diaphram or a simple water barometer. Keeping the house at + 1/4 inch of water or basically any amount of positive pressure versus the outside would eliminate smoke infiltration. This should be possible by having some powered make-up air fan to push air into the house. This seems stupid if you are trying to keep smoke out, right? But the difference is your make-up fan can have a filter on it, whereas if you **** in air through random cracks, you are getting whatever ambient air quality is outside, which you then have to hope to filter out with the furnace filter and air purifiers, but the total volume of smoke might overwhelm them, and it's not going to filter out until it's had a couple passes through the house.

I'm aware of how ERVs and HRVs work but I'm not aware that they actually try to maintain any specific house pressurization. For example, any time you turn on a bathroom fan, it will cause your house to become negative pressure and **** in make-up air through whatever cracks exist, even through the wall passages or in through the crawlspace vents or whatever. I've never seen a house that had interlocks on the bathroom fans or range hood fans to kick on any vents or make-up air.

Pressure control is totally standard in any lab, operating room, or cleanroom though. The internal pressure will always be monitored, with dampers or make-up fans or whatever is needed to maintain positive pressure. I don't think anything super elaborate would be needed to keep smoke out of the house, I'm just thinking something like a single duct fan with a HEPA filter on it, that you can just switch on whenever the smoke is bad outside. You could maybe spot-check it with a water barometer to see if it's actually keeping the house pressurized or not.

 

[whateg01]

unless you have window air conditioners it is not likely. I'm not sure how well a heppa filter would work for smoke . just not something I can comment on.

Window AC just recirculates air inside and draws outside air across the condenser. Except for the condensate line there's no path from one to the other unless there are leaks around the window unit.

Not directly related but it does talk about providing positive pressure.

 

[WildBill]

We gets 2-3 weeks of smoke every summer now. It has been terrible the last couple days. I run a couple of big stand alone hepa filters and shut off the outside air intake when it gets bad. I added a manual valve/flapper in the outside intake pipe so I could shut it off when needed. Works great, cost about $1,200 for the three really good hepa filters. I also built a Corsi fan filter box for my shop, it definitely helps a lot with smoke and other stuff.

 

[The Cobbler]

Window AC just recirculates air inside and draws outside air across the condenser. Except for the condensate line there's no path from one to the other unless there are leaks around the window unit.

I agree, but they are probably not perfectly sealed, thus my comment

 

[fitter30]

Positive pressure ever walk into a restaurant or office building where the door is either hard to open or blowing open a inch or more thats pressure. 36" x80" door has 2, 880 sq inches 5 sq ft. 1/4" water column of pressure on a 36" x 80" door = 6.5 lbs

 

[Rusted Nut]

I’ve done quite a bit of hospital construction, where positive pressure is used for infection control. Yes, all you need is filtered make up air; just a bit more of it than your exhaust air. I think it would be pretty expensive to filter out smoke though. Hospital air filtration is complex and costly.

 

[JackOfDiamonds]

thanks to the miracle of targeted advertising I became aware of this ERV unit:

Pioneer® ECOasis 150 Ductless Wall-Mounted Single-Room Wi-Fi Energy Re

Summary Elevate your home's air quality with the innovative Pioneer® ECOasis 150 Ductless Energy Recovery Ventilator. Designed to address the most demanding indoor air quality needs, this cutting-edge system incorporates a PM2.5 sensor, comprehensive air filtration, and an 82% efficiency heat...

www.pioneerminisplit.com

It says "

• Slight positive pressure ventilation with a 60/40 outdoor air to recirculated air mixture ensures a constant supply of fresh air

So I wonder if all ERV units are actually designed to have positive pressure balance. Also I wonder if this dinky little unit would really make any difference in my big house at all.

 

[pcmeiners]

"This versatile and efficient unit is ideal for room sizes ranging from 200 to 500 square feet, ensuring optimal air quality in your living space."

Only good for one small room.

 

[dcg9381]

The only practical way I know of to get "positive pressure" into your home is to pull air from the outside.
It sounds like the last thing you want is to pull in outside air.
I'd be surprised if HRV units can deal with really poor air quality, but might be able to moderate some air quality issues.

 

[whateg01]

The only practical way I know of to get "positive pressure" into your home is to pull air from the outside.
It sounds like the last thing you want is to pull in outside air.
I'd be surprised if HRV units can deal with really poor air quality, but might be able to moderate some air quality issues.

As long as you can sufficiently filter the air you draw in, it should keep the contaminants from entering from other ways

 

[Kaizen]

thanks to the miracle of targeted advertising I became aware of this ERV unit:

Pioneer® ECOasis 150 Ductless Wall-Mounted Single-Room Wi-Fi Energy Re

Summary Elevate your home's air quality with the innovative Pioneer® ECOasis 150 Ductless Energy Recovery Ventilator. Designed to address the most demanding indoor air quality needs, this cutting-edge system incorporates a PM2.5 sensor, comprehensive air filtration, and an 82% efficiency heat...

www.pioneerminisplit.com

It says "

• Slight positive pressure ventilation with a 60/40 outdoor air to recirculated air mixture ensures a constant supply of fresh air

So I wonder if all ERV units are actually designed to have positive pressure balance. Also I wonder if this dinky little unit would really make any difference in my big house at all.

Nope. I have a decent erv in my basement and as most of these units have small filters i doubt it would help. They are designed to bring in air.....no matter what it is. It brings in smells more then if i were not using it. For example with all windows closed in the house i might not smell a neighbors bonfire. But with this thing i can smell it immedietley. The carbon filters are skinny like on a stove hood. And the fans are usually very weak so they won't pull very well theough a thick hepa filter.
I'd get some good room air filters to start with and see how you like those. You'll get more bang for your buck.

 

[pcmeiners]

"The carbon filters are skinny like on a stove hood"

For carbon filter to remove smoke or any other smell they need to be very large, with a large amount of surface area, like a couple hundred pounds of activated charcoal. The bull **** carbon filters companies put in residential retail filters is just to fool the average consumer.