HRV w/ Smoke Filtration
We just remodeled a 1000SF house with closed cell foam in walls and roofline. I have a small loft in the middle and attic space all the way around it, so pretty good access to all first floor room ceilings and some room for equipment (2 bedrooms, 1 bath, combined living room and kitchen). We also have a 2′ tall crawl space underfloor that is accessible from outside.
I live in dry climate. Temps in the summer reach 80-100 and temps in the winter 0-40. I live in an area that has wildfire smoke in the summer.
We have 1 head minisplit in living room for heating and cooling of entire house.
Currently have to keep a few windows cracked in order for to get fresh air, but I am concerned that this will be a problem when it is smoky. Wondering if HRV would be a good idea and if there is one that can filter smoke. Looking back, we probably should have put in central system with filters, but I think that ship has sailed.
Thanks in advance.
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Most balanced ventilation systems I'm aware of are available with filters up to MERV-13, which should filter out most wildfire smoke. If you can find units with higher filtration levels, up to MERV-17, that should capture all smoke. Of course the finer the filter, the more energy required to push air through the filter.
https://images.squarespace-cdn.com/content/v1/5f0893d2fe49967f7825d046/1626893181024-GUVPGVDY35LKRHQ179MV/MERV.JPG?format=1000w
A MERV 13 filter will remove most of the particulate as Michael says. You need an activated carbon filter to remove the smoke smell.
ah, was going to say, I have a MERV-13 in my Panasonic Intellibalance and was definitely able to smell some smoke when there was a nearby fire.
Thanks for you input. This is one I have been looking at and seems very popular.
Do you still run it when it is smoky out? I've never experienced "filtered" smoke, is the smell tolerable knowing that it is not harming you?
Any suggestions on specific units?
Some of the ones I have been looking at:
Panasonic intellibalance 150,
Broan AI B150H75NT,
Zehnder Confoair 160
Broan HRVH100s (HEPA)
I am a bit concerned with the filter cost on these units. How often will they need to be changed? Does it make more sense to have inline filter instead of relying on built in?
I tried desperately without luck to dig up a fairly lengthy thread here where this was discussed, but the gist was that you’ll need a bit of positive pressure to truly break the relationship between the level of smoke/pm2.5 outside and the amount inside. There are a lot of ways to accomplish this, but I believe that the Panasonic ERV allows you to do that after looking over the manual. There are other, more economical ways as well.
Merv 16/HEPA is also helpful in filtering the air that’s supplying the positive pressure. Merv 13 will only get about 75–80% of the pm2.5 matter if memory serves. As others have mentioned, even then it doesn’t get rid of the smoke ‘smell’ entirely which is usually attributable to VOC. Activated carbon filtration can help with this, but the positive pressure offers the best relief in any of our tests.
One thing to note is that adding external inline filters to the HRV can cause quite a bit more static pressure than intended, so testing them and using them minimally during the worst smoke events is ideal.
One strategy that we’re beginning to experiment with is a Merv 13 filter on the positive pressure supply, and then one or more CR cubes to make up the additional needed filtration inside the building envelope. We haven’t tested it yet, but are hopeful based on the CADR of the CR cubes.
Just an update, I have purchased the Panasonic Intellibalance 100, but not yet installed. Does anyone have any suggestions on filter setup for incoming air?
I use a Fantech FB6. If you mount it on the fresh air intake to the ERV, it needs to be insulated.
It takes a mostly standard 10x20 filter so you can buy them in bulk which are much cheaper than the built in one. It is also much larger area, so it will last longer. You can also get an activated carbon one for smoke.
You do have to take some care as some 10x20 are just a tad too large such as the 3M ones. The filter needs to be 9.5x19.5.
You can also look at one of the many multi stage hepa filter systems such as the HS3000 and not power the blower. These are more expensive but get you much better filtering.
Your local HVAC sheet metal shop can also fab you up a filter frame with 6" duct connections to take standard furnace filters. Probably the best value and most flexible as the filters would be stock at your local box store. If you go with a 20x25x5 frame, you can even get a Merv 16 carbon filter. Because the filter is so large, it will last much longer.
So I installed the Intellibalance 100 and fired it up yesterday! Ended up using 6" insulated flex for intake on exterior wall and exhaust through the roof. I used rigid 6" trunk with 4" flex for the lines to the ceiling supplies and exhausts. No additional filtration yet, figured I would see how it does with the built in filter. Immediately saw a huge drop in CO2!
So, I just set the cfm for supply and exhaust to be equal at 70cfm to start, is there anything else that needs to be done with this unit to balance properly? Is there a way to tell if the house is at positive or negative pressure without special equipment?
@brian_wiley, the thread you were looking for is likely this one. Filtering fire smoke with an external filter (as in outside the building) is discussed along with filtering options for inside the home.
https://www.greenbuildingadvisor.com/question/plans-for-external-erv-intake-filter-box#comment-266575