Replies

1. 
   joshdurston | Dec 04, 2020 01:08pm | #1

   Pre-Filters are good, keep in mind you'll have to insulate the enclosure to prevent condensation.
   I would try and find a prefilter solution that accommodates 4" thick standard furnace size (16x24x4??) filters. I don't think that box has much more surface area than the internal filter would have.
   With an HRV (not ERV) you can often wash the core, but having some decent square footage on your return filter will increase the service interval and/or reduce the airflow imbalance that occurs as filters slowly accumulate debris.

2. 
   JC72 | Dec 04, 2020 01:47pm | #2

   I don't see any reason to unnecessarily reduce the flow of outside air into the ERV/HRV. These systems are not designed to require a pre-filter.

3. 
   user_8675309 | Dec 05, 2020 12:07am | #3

   Just be careful on cleaning the stock filters. I have a Broan HRV160 with the ECM motors and the filters are very fragile. I wash them in a sheet pan that usually I use for baking but needed a flat surface to immerse these in. If you are not careful the filter separates from the frame quite easily and it is a bear to get them back in. Broan does not view this as any type of warranty issue, as I tried. And with new ones costing $60-80 they are not something you want to replace often.

1. 
   prairieburner | Dec 05, 2020 10:18am | #4

   Thanks for the reply! That's great to know.

   How do you like the machine? Quirks or issues? I've had no luck finding reviews or real-world info about this device.

1. 
   user_8675309 | Dec 07, 2020 01:27pm | #6

   Other than the fragile filters I have no complaints. I have had this in operation for just over 2 years, running 24/7 on low ventilation mode except during the summer I have it off when I can have windows open in the house. I am up in Anchorage Alaska so it runs 8 months of the year. I think the hardest part of the whole process was learning/figuring out/installing the duct runs. I felt lucky to find a guy who does this for a living in Fairbanks who was super helpful with all my questions. If I hadn't gutted my basement I would not have attempted this, but since everything was exposed it certainly was easier, though not simple. In conclusion, I am happy with the unit and glad I put it in.

4. 
   prairieburner | Dec 05, 2020 10:26am | #5

   Thanks for the replies everyone.

   I was thinking of dust/pollen from the outside airstream and cat fur/etc from the inside airstream prematurely fouling the expensive device filters.

   I figured the 10x10 (100 sq. in.) filter wouldn't restrict the airflow of the 6in round (28.27 sq. in) ductwork.

1. 
   user_8675309 | Dec 07, 2020 01:44pm | #7

   I like the idea of a prefilter a lot, but agree with Josh above about insulating the enclosure, which would be tricky to accomplish. Speaking of filters, check out this site about a nice set up to filter the air(after it goes though the HRV, though) http://ventsolutionsfbx.com/home . Only other thing I can suggest is to find a long bottle brush that will fit into the drain tubes and clean the gunk/funk out that tends to accumulate after awhile.

5. 
   charlie_sullivan | Dec 07, 2020 02:47pm | #8

   Zehnder has prefilters on each exhaust vent. It's a bit of a hassle to walk around to each and replace them, but they are cheap and help keep the ducts clean, as well as saving the more expensive filters. Then there's also a filter on each incoming air stream on the unit itself. I have mine set up with a prefilter on the incoming air outside air, which gets dirty enough that I am glad I have that to save the more expensive filter on the intake of the unit. Because there is a lot of wood smoke in my area, I have a carbon filter on the supply air after the unit. The carbon filter works better after the temperature and humidity are moderated.

6. 
   graygreen | Mar 22, 2024 08:26pm | #9

   The approach I am settling on is to use cheap filters supplied by the manufacturer on the initial ERV intake. After the air comes out warmed you can easily put a quality the filter box there. Most ERV companies have Merv8 filters as their cheap option and then charge a tremendous amount for Merv13 or HEPA. Broan AI has a washable Merv8 filter. I saw DennisWood using this approach here: https://www.greenbuildingadvisor.com/question/ductwork-insulation-vapor-barrier-questions#comment-261715
   https://www.greenbuildingadvisor.com/question/inline-air-filter-boxes#comment-243770

7. 
   DennisWood | Mar 23, 2024 12:11pm | #10

   @greygreen , yes, it's easier to filter on the warm side, but you do need to leave at some filtration in the unit for the core. What you suggest though is likely the best solution for a completely "inside" solution with respect to cost and simplicity.

   My preferred method now, which eliminates the internal ERV/HRV filter altogether is to do filtration outside. This way you have great filtration, up to MERV16 in my case, with less restriction than than OEM filter in the ERV. You also don't need to insulate the box as it's outside. With the winter we've had (very, very low snow cover) the predictions are for another bad year of wild fires. My expectation is the carbon "scrubbing" setup will be used for a few months again this year. We had temps below -30C this winter, and the system worked with zero issues. In the end, it's also cheaper as you can pick up the MERV 16 X1665 filter for around $100 USD, with a 1 year'ish life span. For winter, the HRV intake filter is a much cheaper Filtrete MPR1000 (16"x24"x5"). The box is suspended there on a french cleat, so easy to remove if needed.

   Because the HRV in my setup uses a central stale air return, I've also sorted MERV10 for that (again, eliminating the restrictive internal filter) for a very free flowing 16x25x1. I was able to back off the EC motor settings 15-20% overall (so less watts/CFM) with this external filtration vs the OEM filters, while increasing filtration far beyond the OEM filters.

   
1. 
   graygreen | Mar 24, 2024 06:06pm | #11

   That's a brilliant setup.

   It would have to be modified for a basement ERV setup where the duct is coming out close to the ground. I suppose the filter box could be placed above the wall penetration and the duct would be mostly vertical.

   My other concern is how to actually build the box and build it airtight. Can I use an off the shelf filter box like one of these and add a bug screen at the intake? https://www.hvacquick.com/products/residential/Air-Filters/Inline-Filter-Boxes/AirScape-SFB-V-Series-MERV-13-V-Bank-Inline-Filter-Boxes

8. 
   DennisWood | Mar 25, 2024 08:57am | #12

   That box would work. I'd just enclose it to keep it out of weather. @tim_in_nc did a great job of this using an off the shelf filter unit:

   https://www.greenbuildingadvisor.com/question/plans-for-external-erv-intake-filter-box#comment-265863

   As far as building a box, I used 3/4" MDO plywood with urethane glue at the joints. The glue expands to seal quite nicely. I just used a piece of scrap steel roofing for the top with a 10 degree slope away from the building.