Turning vanes are very important & help reduce static pressure drop. They should be used everywhere needed, irrespective of added initial costs.

It is important to have an even velocity of air through the filter. Filter racks when used at at air returns (not your case) should be oversized to achieve 350-fpm or less velocity through the filter.

What size filter is it & what tonnage is your air conditioner?

Discuss the issue with your HVAC Contractor/Tech. - udarrell

Here is a link that might be useful: Air Side of Air Conditioning - Checking Static Pressure

I wouldnÂt worry about the turning vanes too much on a residential application. As the bottom loads up it will spread out. All studies show the A/A filters improve in efficiency with some dust on them versus new.

Being a A/A 2200 on a upflow furnace, I doubt they were able to cut the blower compartment opening mush more than 15" high because of the heat exchanger deck. This contributes to the problem. The model 2200 is very square unit versus the 2400 which is rectangular, meaning less height and more depth which may have worked better.

Thanks for your quick responses, guys. Some additional information.

First of all, I just pulled the filter out and took a really good look at it. I may have been misled, as to the bottom portion being dirtier. It seems to be about uniform across the entire face, but there are some very large particles along the bottom, which gave the impression of the being dirtier.

The carrier, which holds the filter medium, is 20 x 25. The medium is 72 square feet. The upstream side of the carrier is open fully to the return drop; the downstream side is in fact cut to 16 x 25, the 4" is 'blocked' off the top side of the housing. The return drop was upsized from 22 x 8 to 25 x 12. The old drop was square.

I would suspect that any turbulence caused by the smaller downstream outlet would have mimimum impact, due to the short distance from there to the blower.

The a/c is a 4 ton, 2 stage (replacing a 4 ton SS); the furnace is a Rheem mod 90,000 BTU (replacing a SS Rheem 125,000 BTU). Both were 20 years old and much noisier in heating and cooling.

While I didn't get static reading on the old system, I did get readings on the new. Running a/c in 2nd stage, reading was .58. My maximum CFM in heating will be 1200 (will rarely see that), so I calculate that heating static will be about .4 (maybe less).

I originally proposed the model 2400 to my contractor. He felt that the 2200 would work better with the wider drop.

Thanks, guys.

V

There are multiple problems here:
1. IMC para. 605.3 requires even distribution of air across the filter; there's a Code violation.
2. The initial pressure drop goes from 0.17" to 0.25" because he blocked off the 4"; that's four to five times the "PD" of a conventional filter (you're operating the filter at 576 FPM on high cool).
3. The "blockoff" is probably a violation of the Aprilaire Installation Instructions, which would be another Code violation.

You need a real duct fitting at the filter inlet (that would be one with a "throat" between the vertical duct and the top of the filter) which has a low "Equivalent Length" (A vaned elbow or a true radius elbow - that's one with radii at throat and heel), and a 6" long transition fitting between the filter and the furnace.

You didn't report the SP at the return, if it's over -0.42" you'll probably have blower problems; those things are expen$ive, too.

FERD

Where are you coming up with code violations on a standard and typical residential cold air boot return drop?

Also remember there is space between the pleated filter and the housing before entering the blower housing opening.

Quoting ASHRAE on a simple residential install as a code violation that has no enforcement in that arena is a bit overboard, in my opinion

Ferd, welcome to the board!

Zl:

There is no space between this filter and this furnace, as I understood it (it's mounted on the side on the furnace), AND the installer has blanked off 4" of the filter, because the furnace opening is shorter than the filter opening. I have 24 years' experience measuring where excessive pressure losses occur in duct systems (I decided to focus on that early on, because no one in our area had a clue), and here we see a prime example; you may think me "overboard", but you can take my analysis to the bank. And Thank You!

The space would be in the pleats, and you work with the filter size manufactured.

Everybody wanted shorter furnaces to fit a-coils in short basements so, we got them at the sacrifice of capable openings into the blower compartment.

Certainly if this restriction had been on the downstream side of the blower such as on a commercial unit without an appropriate transition and plenum, there would be a problem.

If you wish to argue the point, ask the furnace manufacturers, why they ship a 14-1/2" x 25" horsehair filter and rack for a 120,000, 4-ton drive with a furnace. The ESP may be high, but the blower will work.

Again in the north, short radius return air drops are common and nicknamed "Buffalo Boots". Commonly they are 20", 24", 26" deep by 8" , 10" or 12" wide.

No code violatitions can be made, just a customer with a potential noisy and loaded motor.

Well, the horsehair is a lesser filter (that's just to keep the "chunks" off the coil, it does nothing for Air Quality), with a correspondingly lower PD; the better the filter, the higher the pressure drop and the higher the potential for problems.

All I did was buy an Alnor velometer kit and start measuring duct pressures to determine why systems weren't delivering rated airflow. People were saying "It's just a return", and I guess they still do today; point being I've found the return is where most of the problems occur, hence the case in point. That installer "strangled" this blower.

"Buffalo" is an ACCA 5I (see Manual D, page A3-14), equivalent length 45 feet; I doubt the "designer" knew anything about Manual D, so I would prefer to see a less restrictive 5J (15 feet) or a 5K (10 feet). The pressure drop improvement goes to the supply side, and then you can balance airflows to increase airflow to the farthest outlets.

See Figure 4 on the Aprilaire Installation Manual for the required transitions. It's nice to be here.

By the way, Figure 4 shows how to install the filter in a "Buffalo Boot". You should check it out. I learned something today.

Hey guys, I appreciate your feedback.

Coincidentally, yesterday, I removed the bottom panel (blower housing) to check the settings on my dip switches and looked at the downstream side of the filter.

While the (metal) filter housing is mounted flush with the furnace wall, the carrier (plastic housing), sits back from the edge of the metal housing, and the filter sits back from the carrier edge. I could 'see' the entire downstream face of the filter.

I estimate (by memory)a gap of 2 - 3 inches; maybe more. There is also the possibility of removal of about 2+ inches of sheet metal (upper, long edge of filter housing) from the furnace.

I will discuss options with my contractor.

Thanks.

V

Great V

Always best to open metal up as most as possible, as long as you donÂt affect the integrity of the blower/heat exchanger shelf.

As far as the gap, between the filter, media and cabinet, the air will make it. No different than having a 16 x 25 filter grill in a wall with a 16" collar and return duct.

When in doubt, read the Instructions; you may find they dictate maximum dimensions for the return opening. You can go bigger than that (it's physically possible), but you might want to check with the factory Service Department before doing so; it's possible there's a reason the dimensions are spelled out (Carrier 350MAV @ 23-1/4 x 14-1/2 regardless of cabinet size or capacity is one that comes to mind).

Sure the air will make it, no one said it wouldn't. I'm only concerned with PD and how it affects airflow.

Thanks Ferd, you have a good point there. I've poured through the manual a few times and don't recall seeing any such statement, but the dimensions (cutout) seem to be the same (height-wise).

Also, looking at the illustrations, there isn't that much room until you're in the blower compartmentl I think I'll leave well enough, alone.

V

http://www.aprilairecontractor.com/products/category/air_cleaners#33

Click on the first Manual. Check out Fig. 4.