Airstrike HVAC (Veteran and Woman owned business) has been helping us with our quarterly HVAC inspections this year. They’re also about to help us in a large way by upgrading the units in woodshop with a significant amount of donated project materials!
The end result will look like an extended HVAC return with two stages of filters. The 20x25x4” boxes will stay on the units where they currently sit. The extension will run down along the wall to a 1” thick filter and be about 7’ to 8’ off the ground. The 1” filters will be something easily changeable, and will prolong the life of the heavier duty 4” filters in the main unit, requiring checks and changes much less frequently. We expect to have to change the 1” filters weekly.
Ask #1.
Given the placement of the drops, HVAC 2 will drop down right above where the miter saw is. In an effort to help prevent dust from blasting directly into the filter, I’d like to get a basic dust hood covering it. Can someone help us get this going in the next 1-3 weeks? Even if it is a few basic pieces of plywood screwed together, anything to help deflect dust down instead of up would be great.
Ask #2
I’d like to do something for Airstrike as a thank you to their technicians and company for helping us out this year. If anyone has some suggestions or means to assist putting a “thank you” together, please let me know! A pen, a plaque on a funky piece of wood, or maybe a peice of metal embedded in a clay body lasered with leather strapping embedded in a circuit board with saw dust 3d printed on it.
To sum it all up, our HVACs should be in much better shape going forward and should help make next summer much easier to maintain.
I’d suggest that we go talk to them and ask if we can make something for them that would be useful in their business, for example, build them some shelves, some storage, a table for a power tool, that is, some project they’d use daily which would make their business better. Don’t get me wrong, Frank’s suggestion is great and nice. But, I’d dunno, maybe I’m more of a practical person, and would hope we could do something for them after what they’ve done for us.
“The end result will look like an extended HVAC return with two stages of filters. The 20x25x4” boxes will stay on the units where they currently sit. The extension will run down along the wall to a 1” thick filter and be about 7’ to 8’ off the ground. The 1” filters w
ill be something easily changeable, and will prolong the life of the heavier duty 4” filters in the main unit, requiring checks and changes much less frequently. We expect to have to change the 1” filters weekly.”
Wait, what?
1” filters in front of a 4”? Pleated paper? How many?
“Staging” filters rarely makes sense.
Static pressure needs to stay under 0.5in WC. Less is always better. At 0.9, you’re looking at system failure. Between, you get poor cooling and high energy costs.
4” 20x25 pleated paper on a 5 ton is about 0.30 to 0.38 in. w.c. when new. It doesn’t take long to load up past 0.5wc. This is already undersized (too much flow resistance) for 5 ton in a woodshop.
But adding pre-filters stacks more resistance and pressure drop. That’s the last thing you want to do.
If you fitted a LOT of 1” 20x25 filters in parallel and then in series with the 4”, and were very selective of where you’re getting the filter media from, the total static pressure could still work when it’s perfectly clean and you, but it doesn’t make much sense to configure like this.
The key problem is the 4” 20x25 filter cabinet, when fitted on a 5ton, is 576 fpm flow velocity. The filters are only rated (generally) for 500 fpm (some say 600) in general use, not a woodshop. That’s not right. Fix the problem you have, don’t put a new problem on top of it.
There will only be one 1-in filter added to make this a two-stage setup.
@dannym I appreciate your concern in this subject and wanting to make sure it is going to help things. I don’t appreciate how you are suggesting this is a completely botched plan without providing a better alternative. A professional HVAC company helped develop this plan. If you have the time and materials to develop a superior plan and donate resources to it I’m happy to work with you on it.
@Kasper Thanks for the measurements! That will save me some time. I’m planning on building the hood this Monday. I’m pretty much just going to copy this video.
There will only be one 1-in filter added to make this a two-stage setup.
There has to be some misunderstanding here. Putting a 1” ~20x25 filter in front of the 4” 20x25 is not viable and will promptly cause failure of the HVAC unit. Absolutely do not do this.
The misunderstanding may be that the configuration isn’t actually 1 filter, and that’s not what we’re doing. Miscommunicated to you, or I’m misreading the description here somehow, sure. My first theory would be that they actually plan to remove the 4” and fan out to multiple 1” and that the description of the plan got scrambled up a bit.
I’m just going the statement I can back up for sure: do not put a 1” ~20x25 filter in front of the 4x 20x25. Imminent failure of the unit would be certain, swift, and potentially very expensive.
