Is my Ac air handler filter the right size

jonboy

Hey all, I replaced my old 3.5T ac 25 yr old unit with new. Approx. 2200 sg. ft. home/ 2 levels with open area in the middle. Everything was working fine, just needed electric back up heat to my wood stove and looking for efficiency. The old was replaced with same size, no changes to duct, no work in the attic...just a new compressor and air handler. No tests or measurements, the company just went off the old size since it was working. Issues....I have 2 return vents that will not hold a Kleenex up to register when running, a few of the others will that are closer to the unit. Also, when the temp outside is 85 it will not keep up with 72 on the thermostat. Runs all day non stop. Again...nothing else was changed, and it was working before. They did tell me they had to put a smaller (hgt wise) unit in do to space. This unit only has a 20x16 filter. The old was at least 22x22 if not a 24x24. Is the smaller filter area not sucking enough? Starving? They did do a temp check and had 49 at the unit and 53 at a register 30 ft away. If i run with the filter out will I be able to tell anything? Do I need a 4 ton unit? Thanks for any help you all can give.

Jamie Hall

At the risk of a stupid question -- what is the capacity of the new unit, in tons?

mikeapolis

Have you tried running the system (carefully) without the blower door? It's really a shame they didn't take the time to run a Manual J. Are you using a cheap filter or something like a 3M Filtrete?

jonboy

Jamie it was a 3.5 ton system, and they replaced with the same size. Trane.
mikeapolis, I will try running with the door off tonight and see what that looks like. I believe they did have a pleated 3m filter in it. I only looked once.
I do have an outdoor wood burner, and they had to put in a heat bank for that. It's been running right now with it out. They thought it might be pulling down the degrees, but that wasn't a problem either. My concern is as soon as I put that back in, which will probably be next week, won't that restrict airflow even more? You all are the experts, but my thought is...the old and new use half horse motors. The old was sucking through a garden hose (per say) with the 24x24...using the same motor, the new is sucking through a straw 20x16. If it was balanced before with a 24x24...how can it be balanced now with a smaller opening? Thanks for responding. The company is working with me, even up to the point of replacement. this has been going on since July. I asked for a pressure test, to see if I was pulling as much as pushing, and I saw them both look at each other, like they didn't want to or didn't have the equipment. By the way , I haven't given them any money yet.

mikeapolis

Those 3M filters really cause a lot of airflow restriction. Having the blower door off then back on during a static pressure test will definitely show what's going on.

ChrisJ

If it's a Trane it might be a positive pressure air handler, so not sure what the blower door being off will do on such a unit.

I'd ask the installer to install an AirBear Supreme 2000 or similar and pay for the upgrade. It's a 20"x25"x5" filter. Use the Merv 8 filter not the 11 or 13.

How is the rest of the ductwork sized?

Zman

Deeper filters have more surface area and therefore much less resistance than shallower.
I keep hearing folks talk up Merv 13 filters to help with Corona. The reality is, unless your fan is sized large enough you will significantly reduce your air flow rates which may be more important. If running a Merv 13, you need to change filters much more often.

ChrisJ

Zman said:

Deeper filters have more surface area and therefore much less resistance than shallower.
I keep hearing folks talk up Merv 13 filters to help with Corona. The reality is, unless your fan is sized large enough you will significantly reduce your air flow rates which may be more important. If running a Merv 13, you need to change filters much more often.

I'm using a 20x25x5 Merv 8 Airbear on my 3 ton system that I intentionally oversized the ductwork on and it's tough to keep the total static at 0.5". Sometimes I get 5 months from a filter, sometimes only 4.

I can't see a MERV 13 working in any residential system honestly unless it's really grossly oversized, like a 20x25x5 on a 2 ton system.

Honestly, it seems like pleated 1" filters have no business existing in residential period.

jonboy

ChrisJ, I will speak to them about it. It is a Trane Tam4A0A36S31EDB model. As far as the duct, it is original to the house. 25 yr old. The only thing i can tell you is there is a bulkhead around the supply line where it pulls air back for the return. If that makes any since? So there's not a dedicated return duct pipe per say. I'm just frustrated because everything worked fine for the last 25 yrs, and now they switched out 2 items (compressor and airhandler) and not working correctly. Uhg! Should have left well enough alone.

jonboy

zman, thanks for the info. I'm not so much worried about covid as I am tested weekly. I see it daily and would rather have covid(which I have had) and my AC running correctly. Probably because I know about covid and not much about AC.lol

Matt_67

A Trane TAM4A0A36 is a 3-ton unit. The 3-1/2 comes with a 20 x 20 x 1 filter slot.

jonboy

Matt_67 I will have to look into that. Thanks for the info. How do you know by the numbers how many ton?

Jamie Hall

On Covid -- folks, it's a virus, not a bacterium. You are NOT going to filter it out without going to a full bore HEPA system, and even then it's doubtful.

ChrisJ

Matt_67 said:

A Trane TAM4A0A36 is a 3-ton unit. The 3-1/2 comes with a 20 x 20 x 1 filter slot.

And, the plot thickens.
What model is the outdoor unit @jonboy ?

Typically a *36 is a 3 ton.

jonboy

ChrisJ, this is bothering me now! Stay tuned as I will have to wait a few hrs to get home. I do appreciate you all helping me out!

jonboy

OK...rest of the story. I checked both unit and they are 3 ton. That's not enough for a 2200sg ft home with cathedral ceilings and sky lights correct? I know it had a 3.5 ton unit before . Let me ask you this...would a 3.5 ton unit have less than a 20x20 filter. The old unit had a odd size filter, like 22 1/4x 22 1/4. Help me get there!!!!

ChrisJ

jonboy said:

OK...rest of the story. I checked both unit and they are 3 ton. That's not enough for a 2200sg ft home with cathedral ceilings and sky lights correct? I know it had a 3.5 ton unit before . Let me ask you this...would a 3.5 ton unit have less than a 20x20 filter. The old unit had a odd size filter, like 22 1/4x 22 1/4. Help me get there!!!!

My system is a 3 ton 2 stage (runs around 2 tons in low) and I have the filter I recommended in the above comment, a 20x25x5" Merv 8. I highly urge you to get one put in.

As far as 3 ton vs the size of the building that all depends on the building's construction, where you live and what you like.

I have 3 ton in a 1600sqft house and I max it out every summer, but I like it 72 during the day and 68 at night and my house leaks like a sieve and has very little insulation. If the 3 ton keeps you comfortable, then it's ultimately better because it's cheaper to run, cheaper to replace and should keep humidity slightly lower on cooler days

If the system doesn't keep up and things end up too warm for you, no, it's not enough.

jonboy

ChrisJ, I'm going to call the company today. I'm sure he is going to say "he thought the old one was a 3 ton". Does any 3.5 ton unit use a 20x16 filter or would it need to be bigger? Reason is, I have no paperwork to prove it was a 3.5 ton. I only know the size of filter, and it worked fine with a bigger filter. They have already disposed of old unit. Just my knowing it was, is all I have right now. Other than it's not working correctly with what they have.

motoguy128

What’s your location? Sorry if I missed it. 85F, sunny, humid may be close to design conditions if you in a northern climate. So running all day to maintain 72F may be spot on. Longer a system runs, the more efficient it is.

EdTheHeaterMan

A two-stage unit will run all the time. That is what it is supposed to do. With the single-stage unit when the thermostat is satisfied the compressor goes off. With a 2 stage unit when the thermostat is satisfied (for the second stage) the compressor drops to the first stage (not Off). If the low stage is enough to meet the load, Then it will go off... but mostly it will not and just continue to run on Low until the indoor temp increases to the point where the Second stage comes back on. During the warmer months, if your 2 stage system actually goes off. It is Too Big.

That said, Were you comfortable all summer? Yes... correct size, if not, then 3 Ton may not be large enough and you will need to go to 4 Ton. (Unfortunately, They don't make half-ton sizes in 2-stage.)

Edit: the smaller air filter may also contribute. First I would use a larger surface air filter indicated above by others. (pay for the upgrade but size for 4 ton AirBear suggested above) Have the installer put in writing (by email or letter) that they agree to install a 4 ton 2 stage next year if the larger filter does not solve the problem. (that is why you should get the larger capacity air filter now) I would also let them know that you are willing to pay for the larger size. (As if the system was installed that way in the first place. The difference only not for the extra labor)

3 ton TAM4A0A36 is 17+" wide
4 ton TAM4A0A48 is 23+" wide

That may be an issue. the location opening may need to be increased.

jonboy

Great, thanks all. I will get with the company and see what they say about the bigger filter with the same unit. To be continued!

GW

Too small, 2.22 sq ft of filter for 1200 cfm- 545 feet per minute. 300FPM is good, but sometimes the math is hard to achieve without redoing the whole thing (more money)

try to be mindful how you communicate all this. Some homeowners can pull this off well, other homeowners are prickly and that’s when the fun starts 

GW

After more contemplation, Trion Air Bear rates their filters in the 500s, but these are larger pleated filters. A little 1” filter- not super good 

jonboy

Thanks GW. I'm good with the company. In fact they do alot of work for me at my job, and I have the say so on who does the work. Not going to use that, but it just seems like they are dragging their feet and I don't have any patient.lol He did say he might have to call in his air guy.lolllll I think if it was me, i would have already done that. I'm sure they are crazy busy, but you have to take care of customer,(finish the job). I will keep you all up to date on what I find out.

jonboy

OK, I'm back with the final episode..lol Looks like they are going to switch it out to a 4 ton unit in a couple weeks. They said that they usually don't put in 5 inch filters,(air bear) maybe 2 inch, but most of the time 1. I'm guessing the 4 ton trane is probably going to come close to a 20x25 filter. Am I close? I did pull the filter out of the 3 ton and I could get the return air that wasn't pulling anything to suck smoke back through the grill, which it wasn't before with the filter in. So I'm thinking bigger filter, bigger unit...should be back to what it was before the caos

ChrisJ

jonboy said:

OK, I'm back with the final episode..lol Looks like they are going to switch it out to a 4 ton unit in a couple weeks. They said that they usually don't put in 5 inch filters,(air bear) maybe 2 inch, but most of the time 1. I'm guessing the 4 ton trane is probably going to come close to a 20x25 filter. Am I close? I did pull the filter out of the 3 ton and I could get the return air that wasn't pulling anything to suck smoke back through the grill, which it wasn't before with the filter in. So I'm thinking bigger filter, bigger unit...should be back to what it was before the caos

Sigh.........
The 5" filters restrict the system much less and go longer in between changes. I would insist on it.

That being said, can your ductwork handle 4 tons?

jonboy

Not for sure on the duct, I do know the old unit was a 3.5 ton. Would there be a big difference in duct from 3.5-4ton? Because it handled the 3.5 for 25 years.

ChrisJ

jonboy said:

Not for sure on the duct, I do know the old unit was a 3.5 ton. Would there be a big difference in duct from 3.5-4ton? Because it handled the 3.5 for 25 years.

Several things.

Most if not all new residential air handlers want to see very little static pressure. Just because one from 25 years ago tolerated it doesn't mean a new one will.

If the ductwork was already undersized, going 1/2 a ton bigger isn't going to help anyone.

pecmsg

If that system is operational have a TESP (Total External Static Pressure) test performed. This will tell you exactly what your duct system can handle.
Most systems were seeing are oversized on undersized ducts. Going from 3 1/2 to 4-Tons compounds the problems. Excessive noise being one. If the new system has a ECM blower it will kill that motor and there not cheap!

jonboy

The company told me they don't make these units in half ton, so they had to go to a 4 ton unit. He stated that with the variable speed motor, the duct work shouldn't be a problem and the unit should be quieter than the 3 ton in there now. They will have to rework the bottom of the unit to fit it in because it is a taller unit. that's where I am right now.

pecmsg

Still have the duct work checked. You might be able to go down to 3-Tons!

GW

Seems odd- we routinely downsize ac systems. Kinda wonder is the system you have now was set up correctly 

EdTheHeaterMan

pecmsg said:

Still have the duct work checked. You might be able to go down to 3-Tons!

He already has a new 3 ton, the company is increasing to get back to 3.5 ton that was working before they installed the new 3-ton that is problematic

The problem is the variable speed model does not come in 3.5 ton... only 3 ton or 4 ton.

pecmsg

EdTheHeaterMan said:

pecmsg said:

Still have the duct work checked. You might be able to go down to 3-Tons!

He already has a new 3 ton, the company is increasing to get back to 3.5 ton that was working before they installed the new 3-ton that is problematic

The problem is the variable speed model does not come in 3.5 ton... only 3 ton or 4 ton.

Sorry
I missed that part

jonboy

ok guys/girls...they installed a 4 ton Trane with variable speed. 24x24x1 filter. They had to install the hydo- heating coil for wood burner pre-filter do to space...so sucking air across the coils instead of blowing across up top. Electric back up heat to turn on if water temp goes below 120. They still only used a 1 inch filter. If I can't get that changed, is there a 1 inch filter that works better than others? I had a washable one before, and to be honest, I kept it for 20 years.

EdTheHeaterMan

You will need to find a way to put a filter before the HW coil. any dirt in the air will be able to build-up on that coil and eventually block ait flow. A pleated 1" filter should be rated no greater than MERV 11. They are usually a lower price. 3M Filtrete premium filters have more pleats but may also be more restrictive.

That is my opinion

Another issue with all that heated air from the HW coil will make the motor operate at a higher temperature. That can't be good for the motor. This guy designing your system has some serious inexperience issues. You may need to teach him the hard way by getting the wood stove cranked up to 180° or 200° and run that motor to the limit until it burns up!

Or let him read this comment from a

45 Years experience HVAC contractor,
Oil Heat / Hydronics and Duct system
Serviced and Installed since 1978
Cleaned oil heaters since 1974

I already made that mistake in the 1980s

ChrisJ

EdTheHeaterMan said:

You will need to find a way to put a filter before the HW coil. any dirt in the air will be able to build-up on that coil and eventually block ait flow. A pleated 1" filter should be rated no greater than MERV 11. They are usually a lower price. 3M Filtrete premium filters have more pleats but may also be more restrictive. That is my opinion Another issue with all that heated air from the HW coil will make the motor operate at a higher temperature. That can't be good for the motor. This guy designing your system has some serious inexperience issues. You may need to teach him the hard way by getting the wood stove cranked up to 180° or 200° and run that motor to the limit until it burns up! Or let him read this comment from a 45 Years experience HVAC contractor, Oil Heat / Hydronics and Duct system Serviced and Installed since 1978 Cleaned oil heaters since 1974 I already made that mistake in the 1980s

And here's my beef..

The 20x25x5" merv 8 airbear is rated for a 0.23" pressure drop on a new filter at 1600 cfm.

A 1" filter of similar dimensions will be too restrictive even at a merv 8, forget about higher to achieve a total drop of no more than 0.5" across the air handler.


Here's pressure drops across 1" pleated filters.  I come up with 580 fpm @ 1600 on a 20x20 so that's your entire allowed pressure drop of 0.5 across a 1" pleated 20x20 merv 8.  Nothing left for duct work or the filter getting dirty.