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Rob Will
03-01-2008, 11:10 PM
Here is my HVAC system that doubles as an air cleaner in the woodshop.
It is a Lennox Pulse Furnace (sealed combustion) equipped with a three-stage air filter system.

The primary filters are cheap 20x20 fiberglass filters placed back to back with a slightly tighter 3M Allergen filters. There are two sets of these so the total intake area is 20x40. (the first filters are slid back slightly so you can see the second set)

From there the air goes through a Spacegard (Aprilaire) Model 2200 pleated media filter. There is barely a trace of dirt on the Spacegard.

In order to monitor how much static pressure my furnace is working against and the condition of the filters, I installed a Dwyer Magnehelic gauge (eBay, $10) on the wall that reads 0-2" H2O. The gauge is connected to the fan intake section of the furnace with a 1/4" polyethlyene tube.

Here are the static pressures as measured with the furnace running:

No filters: 0" H2O
Spacegaurd only: 0.20" H2O
20x20 filters only: 0.10" H2O
All filters combined: 0.30" H2O
Filter intake blocked: 1.25" H2O (zero flow)

The system is moving about 1200 cfm and it is distributed through a duct running the length of the shop. Thus far, it seems to be doing a much more effective job than my Delta air cleaner. It is more powerful and easier to service.

Thanks for looking.

Rob

Keith Spaniel
03-01-2008, 11:21 PM
Looks good, Do you know How many microns the 3m filters are?
keith

Rob Will
03-01-2008, 11:52 PM
Looks good, Do you know How many microns the 3m filters are?
keith

Hi Keith,
I'm not 100% sure but 3M's website says up to 58% efficiency on particles 0.3-1 micron. To be conservative, let's say it will get 1/2 of the 1 micron particles every time they pass through. (?)

The Spacegard claims about the same performance with new filters (46% @ 1 micron), and somewhat better when the filters are partly used (75% @ 1 micron).

Rob

Eric Haycraft
03-02-2008, 12:16 AM
If you really want to go all out on filters, check out iaqsource.com. That's where I buy my furnace filters now. From them I was able to get a merv 15 filter for my house. That is just below a hepa.. instead of 99.97 percent of .3 microns, it is like 99% of .3 microns. merv 16 is essentially hepa. They also have charcoal filters that will fit my delta ceiling air filter.

Thomas Canfield
03-02-2008, 12:30 AM
Rob,
a hange
I had planned on using my heat/AC air handler as a filter similar to yours with extra box and filters, but found that the low suction did not really get the airborne dust out of the air. I later installed a box fan with 20x20 filter taped to the fan (WOOD Magazine suggestion) hanging above head height and that has worked much better. I put hanger on the bottom of the fan case the second time to hang it so that the controls were accessible. Might give you some additional dust removal.

Jeffrey Makiel
03-02-2008, 9:36 AM
Home heating blowers usually have forward curved wheels designed to give lots of air flow at very low pressure. Therefore, any additional pressure on the system, the flow significantly reduces. A modern variable speed fan monitored by the fan control center within the furnace provides some compensation, but it has its limits.

I would recommend that you check the leaving air temp with the old filter arrangement versus the new. If there is a significant rise in temp, I'd be concerned.

Also, if your unit also does air conditioning (has an "A" coil), check the temperature differential between the intake air and leaving air and consult a professional. Too much drop will cause short cycling of the outside condenser unit, and inside dehumidification will suffer.

-Jeff :)

Rob Will
03-02-2008, 1:20 PM
Home heating blowers usually have forward curved wheels designed to give lots of air flow at very low pressure. Therefore, any additional pressure on the system, the flow significantly reduces. A modern variable speed fan monitored by the fan control center within the furnace provides some compensation, but it has its limits.

I would recommend that you check the leaving air temp with the old filter arrangement versus the new. If there is a significant rise in temp, I'd be concerned.

Also, if your unit also does air conditioning (has an "A" coil), check the temperature differential between the intake air and leaving air and consult a professional. Too much drop will cause short cycling of the outside condenser unit, and inside dehumidification will suffer.

-Jeff :)

I agree and that's why I installed the Dwyer gauge on the wall. If the filters start to become restrictive, I should know about it. Right now I am seeing about .35" H2O, when it gets to 0.5" (or less), I'll change the filters. Just a thought.

Rob

Jeffrey Makiel
03-02-2008, 5:21 PM
Most home systems have an allowance for only about 0.10" w.g. drop with nominal flow from the get go. That means that the system is set up for simple low restriction filters available for about $3.00 each which are meant to keep the coil and heat exchanger clean, not one's house. Folks generally add more filters (electrostatic) or higher efficiency after the fact to try to improve indoor air quality too.

0.3" to 0.5" overall increase seems high. However, every home system is a little different, and I'm certainly no expert.

Good luck on your strive for a healthier shop. :)

-Jeff :)

Rob Will
03-02-2008, 10:04 PM
From what I am reading, it seems that many residential furnace fans are set up for 0.5" w.g.

One website that I looked at suggested that the filters should not be more than about 20% of this pressure drop..........Ooops, that only allows me to have 0.1" w.g. resistance across the filters (as Jeffrey also pointed out).

Right now, I am simply measuring pressure drop from atmospheric pressure across the filters.

Should I be measuring the total pressure differential across both sides of the fan?:confused: The Dwyer gauge has ports for this.

I can do whatever it takes to make this work.
Any suggestions?

Thanks,

Rob