How to filter wildfire smoke from an intake air system
Like many, our household purchased a mechancial (vs electronic) air filtration device that sits in a room and filters air as a response to the bad air quality that came from wildfire.
Now we are building a new house that will have a heat pump mini-split system, so no ductwork, to heat and cool the rooms. I’d like to install an air intake system that filters air coming into the house, versus opening a window. The latest codes require a whole house exhaust system, which my plan checker says will be met by running continuously then bath fan for a home if our size, less than 1000 square feet. Ideally the intake would have a damper for winter. Since an exhaust system creates negative pressure, the makeup air has to come from somewhere, and in a new, tightly sealed house, I want to have control over the quality of that air. Are there any active (includes fan) or passive filtration systems out there? It seems like this is an aspect of indoor air quality that has yet to be addressed by the building code.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
poindexterous3,
Our code also allows the full time ventilation system to be supplied by exhaust only fans in small dwellings - but it's not a good way to go. Install an ERV/HRV and you can add filtration, as well as benefiting from the heat recovery, and knowing where your supply air is coming from.
I concur with Malcom Taylor. Install a ERV/HRV with a inline filter box added to the outdoor air intake duct like these ones from HVACquick: https://hvacquick.com/products/residential/Air-Filters/Inline-Filter-Boxes
Select the type that works best for your situation, but I suggest going with one of the options that supports at least a 2" thick filter if not multiple filters as that will allow you to add in a activated charcoal filter if needed.
Another vodte for an ERV/HRV and a filter box. If you're close to fire areas and expect heavy smoke often, I'd try to get a thick pleated filter, 2"+ thick (they are commonly available up to 4" thick). I would also put TWO filter slots -- the first (the "first" being the one the outdoor air gets to first) would be a fine particulate filter, MERV 13 or so. The second would be an activated carbon filter. Between those two, not much is going to get indoors from the outdoors.
You want to run the unit continuously during fire season, and have it set to maintain a slight positive pressure within the house. This will ensure that any air leaks leak towards the outdoors, so that nothing from the outdoors is sucked into your home through any leaks that would otherwise be bypassing your air filtration system.
Bill