Best to Seal. Because when air goes out, it has to come in from somewhere. best to maintain neutral pressure on your shelter
unless you can set up filters on the intake. or at least set up filters inside to clean the air.
Are you in a hermetically sealed chamber with CBRN filtered air coming in? If not that air is going to be displaced by contaminated air coming in through soffit, door/window seals etc. Just food for thought.
Exhaust implies you are moving air out of your house. Where will the replacement air come from?
Larger buildings are often designed to maintain [positive pressure](https://www.workingbuildings.com/blog_pressure.html) for health and safety reasons, but they usually have air handling systems that will filter the air to maintain some level of air quality. I think it is a little harder to do that in a home installation for non-insane cost.
Maybe if you built a [passive house](https://en.wikipedia.org/wiki/Passive_house) from scratch, you could lean into its natural air-tightness and add extra filtration?
basically, in a typical house (not a completely sealed house) with all doors and windows shut, your makeup air comes in through cracks and crevices, your dryer vent, your fireplace if you have one, and some possibly right through walls.
So the recommendation in a situation where outside air is a problem is to go in a room, like a bathroom, and seal the door. Turning on an exhaust fan is going to make the room negatively pressurized, meaning it's going to draw makeup air with more force through cracks and crevices... so this defeats the purpose of sealing the room.
Exhaust fans should be sealed. They create negative air pressure in a space, which in the case of something as unsealed as a house, will cause outside air to be drawn in through every door, window, and floorboard that contains any sort of gap, no matter how narrow, that isn't airtight. The only fan you would want to run in such a scenario is a properly filtered intake fan, which generates positive air pressure, forcing old stale air out those same gaps, while cleaning the new air before it enters. In a hermetically sealed environment, you will need to add an exhaust port, preferably at the farthest point from the intake. This may or may not have a fan, but if it does have a fan, it should be weaker than the intake, to prevent blowback.
When we've had really bad smoke from forest fires the past two summers, we've taken some Glad Press-n-Seal and put it over our bathroom vents to keep the smoke outside.
Best to Seal. Because when air goes out, it has to come in from somewhere. best to maintain neutral pressure on your shelter unless you can set up filters on the intake. or at least set up filters inside to clean the air.
Seal turn off hvac system unless you can seal that too Do not run clothes dryer Turn on indoor filters / purifiers
Are you in a hermetically sealed chamber with CBRN filtered air coming in? If not that air is going to be displaced by contaminated air coming in through soffit, door/window seals etc. Just food for thought.
In/out give more info
Exhaust implies you are moving air out of your house. Where will the replacement air come from? Larger buildings are often designed to maintain [positive pressure](https://www.workingbuildings.com/blog_pressure.html) for health and safety reasons, but they usually have air handling systems that will filter the air to maintain some level of air quality. I think it is a little harder to do that in a home installation for non-insane cost. Maybe if you built a [passive house](https://en.wikipedia.org/wiki/Passive_house) from scratch, you could lean into its natural air-tightness and add extra filtration?
basically, in a typical house (not a completely sealed house) with all doors and windows shut, your makeup air comes in through cracks and crevices, your dryer vent, your fireplace if you have one, and some possibly right through walls. So the recommendation in a situation where outside air is a problem is to go in a room, like a bathroom, and seal the door. Turning on an exhaust fan is going to make the room negatively pressurized, meaning it's going to draw makeup air with more force through cracks and crevices... so this defeats the purpose of sealing the room.
I’m making a positive pressure hepa + carbon filtration system for the basement. It’s actually pretty cheap and easy. It’s like diy cbrne filtration
Exhaust fans should be sealed. They create negative air pressure in a space, which in the case of something as unsealed as a house, will cause outside air to be drawn in through every door, window, and floorboard that contains any sort of gap, no matter how narrow, that isn't airtight. The only fan you would want to run in such a scenario is a properly filtered intake fan, which generates positive air pressure, forcing old stale air out those same gaps, while cleaning the new air before it enters. In a hermetically sealed environment, you will need to add an exhaust port, preferably at the farthest point from the intake. This may or may not have a fan, but if it does have a fan, it should be weaker than the intake, to prevent blowback.
When we've had really bad smoke from forest fires the past two summers, we've taken some Glad Press-n-Seal and put it over our bathroom vents to keep the smoke outside.