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Community and Q&A

HRV filter for feedlot smell

Eric_Torrie | Posted in General Questions on

Hi there! I’m getting ready to build my forever home and have a question regarding air filters for ventilation systems.  

I farm up in Canada and my yard happens to be downwind of a large commercial feedlot operation. We have really bad manure smells as often as one day a week (depending on the wind).  

I’ve been reading lots about HRV systems and how they bring in fresh outside air. But what happens when the outside air isn’t fresh? I like the idea of building a tight house and am considering using sip panels for the walls. However if I can’t find a filter that will filter out smells I might just have to do an exhaust only ventilation system and let my house slowly filter the stink out of the air. All the houses in the area are standard stick frame construction with either exhaust ventilation or no ventilation and they don’t seem to stink inside is really smelly outside.  This might be because the walls act as a filter as the house leaks or it might just be that only a tiny amount of air leaks at any given time and it’s not smelly outside long enough for the smell to permeate the house. 

So my question is: are there filters for HRV systems that can filter out these types of smells?

I’m looking into rigging up a sensor system to detect when it is smelly outside and then I would use that to switch the HRV off during those times. I’m not sure how good little arvino sensors are at detecting those types of smells and I’ve got some VOC and ammonia sensors coming in the mail to do some experiments to find out…

Thanks for any thoughts or recommendations!  

Eric

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Replies

  1. User avatar
    Peter Engle | | #1

    The only thing that will effectively filter out organic gases is activated charcoal. There are activated charcoal filters manufactured for portable and stationary indoor air purification equipment that could probably be rigged to work with an HRV/ERV. You need to watch the pressure drop across the filter and make it serviceable. Service schedule would be based on when it's not stopping the stink anymore. I'm not sure it would be worth the effort to switch the airflow through the filter on and off - the cost of sensors and mechanics would probably exceed the cost of just changing the filters a bit more often.

  2. Trevor Lambert | | #2

    "The only thing that will effectively filter out organic gases is activated charcoal."

    And, apparently, the leaky wall assemblies of code built houses.

  3. Zephyr7 | | #3

    You’ll want a large area of activated carbon to keep pressure drop down. Basically that just means the filter will be much larger than the size of the supply duct. Activated carbon is pretty good at filtering out organic compounds like farm smells. HEPA filters can work too sometimes, but those tend to have a lot of back pressure and thus probably wouldn’t work with an HRV.

    You can test any filter you want to try by getting a canister of that type for a respirator. If an activated carbon canister filters the smell out, then you know the same type of filter media will work on your HRV too.

    Bill

  4. Malcolm Taylor | | #4

    The problem I've had with the charcoal filters I've used on vent stacks is that they stop working when they are damp. The filter would probably need to be installed in a location to minimize exposure to moist air.

    1. User avatar
      Mark Walker | | #5

      How damp does the charcoal have to be to lose effectiveness?

      1. Malcolm Taylor | | #9

        Mark,

        I don't know. The ones on vent stacks get soaking wet, so maybe it isn't an issue in ducts. As Akos points out, they have been successfully used for years to mask grow-ops, so we know they work.

        Aren't Hepa filters the recommended way of reducing particulates from woodsmoke?

  5. User avatar
    Mark Walker | | #6

    I'm flanked by neighbors who burn wood outside for the heck of it. My house will smell strongly of smoke when my ERV is operating. Would a charcoal filter remove the smoke?

    1. User avatar
      Peter Engle | | #7

      Probably. Since smoke is a particulate, a HEPA filter would probably also work, but they have too much back pressure for an ERV as mentioned above. Or just turn off the ERV when they're burning fires.

  6. Akos | | #8

    You can get a filter box with a charcoal filter to put inline with the fresh air supply to the house. Your local "hydroponics" suppliers carry a wide variety of these to filter out other agricultural smells.

    Typically you are looking at ~0.5" WG pressure drop at rated flow, so get one sufficiently large to get the pressure drop down to about 0.2" at your HRV's flow rate.

    You would need to have it installed when the HRV is commissioned otherwise it will unbalance the flow.

    HEPA filters are for particulates (soot, pollen, dust), it will not do much for farm smells.

  7. Eric_Torrie | | #10

    Thanks for your thoughts everyone, I'll go do some research!

    Cheers

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