Replies

1. 
   Danan_S | May 07, 2022 02:13am | #1

   An HRV isn't really designed to filter very fine outside particulates like the PM2.5 on it's own. The filters in the unit are more geared around removing dust and pollen.

   I'm in CA also, and I added a prefilter box with stacked very large surface area carbon and merv13 filters to the intake of my HRV, which filters potential wildfire smoke while minimizing static pressure increase.

   There is a small increase in power draw of the HRV to overcome the resistance of the filter, but not much - like 10W.

   It also has the effect of reducing the filtering that the more expensive HRV filters have to do.

1. Expert Member
   Akos | May 07, 2022 11:47am | #3

   Dan's setup is a good one. Making sure the house is air tight also important as any air leaks will bring in smoke.

   During fire season you also want to unbalance the unit to pressurize the house slightly to further prevent air infiltration. Some ERV/HRV can be easily adjusted others might need an inline damper to unbalance enough.

   You can also get an inline filter assembly such as a Fantech HS300 or Lifebreath TFP3000HEPA and plumb it in line with the fresh air feed to the house as shown in the diagram on P10 here:

   https://www.lifebreath.com/wp-content/uploads/2022/04/69-TFP3000-RTO_EN.pdf

   This way the HEPA filter can do double duty and clean both outside fresh air supply and house air at the same time.

   The only change I would do is to add a backdraft damper to the breather T so you can leave the fan off on the HEPA filter most of the year when extra filtering is not needed.

2. 
   Flytrappist | May 07, 2022 07:45am | #2

   When building my new house, I wired a wall switch in the hall next to my ventilation system. The switch has a red LED that lights when the system is OFF. In rural eastern NC, we don't have a problem with wildfires, but we do have hog farms. If there is a rare north wind, we get a blast from the hog lagoon- it will make you reconsider eating pork! I flip the switch, the damper closes, and ventilation stops. A few hours later, the wind shifts and we can start ventilating again. The LED reminds us the system is off, if we forget. You could use the same idea for the really bad smoke days.
   Farmer Karl

3. 
   Danan_S | May 07, 2022 12:04pm | #4

   By the way, here is what my intake filter system looks like

   
4. 
   lewjones | May 07, 2022 02:27pm | #5

   Thanks guys for the great replies. No substitute for experience. I think the very large surface area of the filters is the key to keeping the flow restriction low. I really like the idea of maintaining a positive pressure inside the house. I'll keep that in mind when i pick out an HRV. I hadn't thought of putting the filter downstream from the HRV but why not if we're recirculating some of the inside air. We won't need all that filtration in the winter so I guess we'd either remove filters or create some sort of bypass.

1. 
   Danan_S | May 08, 2022 09:56pm | #7

   > We won't need all that filtration in the winter so I guess we'd either remove filters or create some sort of bypass.

   I'm curious what you think this might save on. It's not much in terms of electricity and also not much in terms of filter media (assuming your filter box is using generic filters and not an ultra premium system like IQ Air).

1. 
   lewjones | May 10, 2022 04:21pm | #8

   My feeling is that we'd get better performance from our ventilation system without the filters or maybe a lower MERV filter. But you bring up a good point - why not have the cleaner air? I have a Fantech in-line fan with a filter box in the Condo where we are now and when I went from a MERV 8 to a 13 when we had smoke the CFM's went down a lot.
   So, I change filters in the winter. With large surface area filters that might not make as much sense.

5. 
   Deleted | May 08, 2022 09:55pm | #6

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