Your HVAC Isn't Moving Air Like it Used to Move Air?

[Jim Koepke]

My home heating unit is having problems at the moment. Like the heat pump thread, either a professional can be called in at a ridiculous rate or it can be DIY. Well at least turning off the breakers and then checking everything with a meter will keep me from electrocuting myself. Just to make sure, the meter was checked to make sure it was working. One of my rules as a troubleshooter is to make sure my test equipment isn't going to become part of the problem.

Many years ago my job was as a field service tech for blue print machines and other types of large copiers.

The larger units used large mercury vapor lamps to expose the photo sensitive sheets. These required a lot of air to cool the lamps. These units used centrifugal fans, aka squirrel cage fans. Over time they lose efficiency due to dust sticking to the inside surface of the air moving veins. It is a tedious job, but someone has to do it.

The instructor during my training class said if you ever do this to your own unit in your home HVAC, don't tell any neighbors because they will want you to do it for them for free. If they ask why it is working better tell them you tightened a loose belt or something unless you like doing the dirty work for free.

Here is a close up of how it looks during the work in progress:

492430

The four on the right have been brushed for the first round of cleaning with an old toothbrush. Note the one near the center has a clip attached at the top. This is to balance the wheel, do not remove this clip. Take care when cleaning around it.

After the first go over with a brush a cotton swab soaked in alcohol will be used to remove any dust or oils that may be missed by brushing.

If you ever clean one of these, you will likely be amazed by the difference in air flow between before and after cleaning.

jtk

[Bill George]

Besides cleaning the fins of your squirrel cage blower. consider your choice of air filter. Air lot of older units can not use the really good paper pleated filters because they restrict air flow too much. The cheap fiber glass filters allow a lot of dirt to pass. In addition if you have a air conditioning coil after that dirty blower then it might be packed also. Look for the MERV rating on the filters you buy, the higher that rating the better it filters.

Those of us with varying speed ECM fan motors like I have can use the pleated 4 inch filter and it removes a LOT more dirt. The control system senses that restriction and increases the motor speed as needed.

[Tom M King]

It's not a good sign that it was able to get that dirty to start with. Even the old ones in our rental houses, that operated most of their life before we even owned them for years, still look clean. I was surprised that they are.

[Brian Tymchak]

Besides cleaning the fins of your squirrel cage blower. consider your choice of air filter. Air lot of older units can not use the really good paper pleated filters because they restrict air flow too much. The cheap fiber glass filters allow a lot of dirt to pass. In addition if you have a air conditioning coil after that dirty blower then it might be packed also. Look for the MERV rating on the filters you buy, the higher that rating the better it filters.


Learned that lesson. For many years I ran MERV 11s in my HVAC system. Then I decided that MERV 13s must be better so I bought those and installed one. Immediately started having the burners cut out due to high temp. Went back to 11s. However over the last year, those also started causing high temp errors. Moved down to MERV 8s. Worked for a bit, but then started having high temp errors again with the filter in. Worked without the filter. The 3rd service tech finally offered a probable diagnosis of the blower slowly failing, along with an undersized duct on the return air side. Also found that the cut out for the return air in the base of the furnace was only about 2/3 s the size it needed to be. Since the system was 24 years old, we ended up replacing the furnace.

So now I have a pile of MERV 8, 11, 13 filters that don't fit the new system.

I now wonder if there was a buildup of dust in the coils. I didn't get an opportunity to inspect them when they were pulled out.

[Stan Calow]

Thanks for this thread Jim. I never thought of this as something easily checked and corrected.

[Bill George]

Learned that lesson. For many years I ran MERV 11s in my HVAC system. Then I decided that MERV 13s must be better so I bought those and installed one. Immediately started having the burners cut out due to high temp. Went back to 11s. However over the last year, those also started causing high temp errors. Moved down to MERV 8s. Worked for a bit, but then started having high temp errors again with the filter in. Worked without the filter. The 3rd service tech finally offered a probable diagnosis of the blower slowly failing, along with an undersized duct on the return air side. Also found that the cut out for the return air in the base of the furnace was only about 2/3 s the size it needed to be. Since the system was 24 years old, we ended up replacing the furnace.

So now I have a pile of MERV 8, 11, 13 filters that don't fit the new system.

I now wonder if there was a buildup of dust in the coils. I didn't get an opportunity to inspect them when they were pulled out.

If it worked fine with the 11s and then not. I can tell you right now undersized Returns were Not the issue!! My guess without being there was your AC coil needed removed and cleaned. When I found dirty blower wheel vanes, 95% of the time the AC coil was also full of dirt. Those cheap 49 cent fiber glass filters are the worst thing you can use. We generally used DA or pleated filters, most units can use a MERV 7 or 8 without issues. Take that fiber glass filter out and use a salt shaker to see if salt passes, if so dirt can also pass.

FYI motor amp draw with a squirrel cage blower depends on How Much Air it moves. Restricted air flow equals Less amp draw. Less air flow, furnace trips the high limit or in AC the coil freezes over.

[Jack Frederick]

Your experience is widely shared Jim. Minisplit users are shocked at the performance increase after cleaning the evaporator wheels too. I suspect My company represented Purlolator filters in the hvac side of things for almost 50 yrs.the old fiberglass filters didn’t start filtering until they were dirty. The terms Efficiency and Effectiveness were used to describe filters. If there was ever a case of “figures don’t lie, but liars figure” it was in the old filter business. MERV ratings are great because they actually gave a test that had some meaning. As Brian found out the learning curve was steep and many system, due to design and construction could not utilize the higher ratings.

[Edward Weber]

I would suggest to anyone with a forced air system to change your filter/s at regular intervals.
I change mine every month. It’s a small price to pay for keeping your ducts, fan, and coils clean.

[Brian Tymchak]

...Those cheap 49 cent fiber glass filters are the worst thing you can use. We generally used DA or pleated filters, most units can use a MERV 7 or 8 without issues.

For the 18 years I lived here with that furnace, I always used pleated filters, 20x25x4, either Trion Air Bear or Honeywell brands. And I agree that the undersized return didn't cause the issue as the furnace worked for many years with it. It's probably a good bet that dirt/dust build up is the ultimate cause of the high temp errors. I wish I had been able to take a look at the coils, but they went up and out of the house and onto a truck in one motion. With the age of the unit (24 years), it felt like the right time to just change it all out. I don't regret doing it, but maybe I'll do a better job of watching for dust build up with the new system.

[Bill George]

For the 18 years I lived here with that furnace, I always used pleated filters, 20x25x4, either Trion Air Bear or Honeywell brands. And I agree that the undersized return didn't cause the issue as the furnace worked for many years with it. It's probably a good bet that dirt/dust build up is the ultimate cause of the high temp errors. I wish I had been able to take a look at the coils, but they went up and out of the house and onto a truck in one motion. With the age of the unit (24 years), it felt like the right time to just change it all out. I don't regret doing it, but maybe I'll do a better job of watching for dust build up with the new system.

If you were using pleated filters the entire time then the ductwork was not the cause unless see below. Over a period of years the A/C coil could of got restricted. Generally speaking the people who do the ductwork undersize the Returns. Why? Because that's what Joe always did?? If you think about it, the same air that leaves the supply ducts, has to return at the same CFM to the unit. I not only saw it on the job, but when I taught ACCA Manual D ductwork design I saw the reason.

So I wonder if these Techs actually checked the discharge air temperature? Its possible the high limit was defective, BUT I have seen Return ducts collapsed if they were flex or undersized, saw a couple times when the Returns were in the poured concrete floor that had collapsed.
The beauty of the varying speed ECM motor it can overcome crappy duct design and other screwups as its looking for a certain amperage draw= design CFM.
Its not how often you charge filters, its the grade you use!! I change my 4 inch MERV 11 once or twice a year.

[Edward Weber]

Its not how often you charge filters, its the grade you use!! I change my 4 inch MERV 11 once or twice a year.

I think it's both
Not everyone (including myself) uses a 4" thick filter, all systems are configured differently.
The most common size filters by far are the 3/4" or 1" style. I use a MERV 13, and it gets changed monthly.

There are many people that don't think about preventative maintenance like a technician. Out of sight, out of mind, until something goes wrong.
Changing a filter, even a less than premium one, at a regular interval, whether it be monthly, quarterly or whenever, goes a long way toward system longevity.

[Bill George]

I think it's both
Not everyone (including myself) uses a 4" thick filter, all systems are configured differently.
The most common size filters by far are the 3/4" or 1" style. I use a MERV 13, and it gets changed monthly.

There are many people that don't think about preventative maintenance like a technician. Out of sight, out of mind, until something goes wrong.
Changing a filter, even a less than premium one, at a regular interval, whether it be monthly, quarterly or whenever, goes a long way toward system longevity.

In a framed filter 1 inch 2 inch and 4 inch size are the only ones I ever saw in 35 years of commercial HVAC/R service. Unless your building is packed with dirt, your doing industrial manufacturing or your taking in a lot of dirty outside air a 1 inch MERV filter should not need changed every 30 days!! A 4 inch pleated filter has 4x the surface area than a 1 inch, less pressure drop, I am surprised your HVAC people did not suggest one when they installed your new unit?

[Edward Weber]

I was talking about my home, Just as the OP was

[Edward Weber]

Then you need to have a talk with your cleaning service!! FYI when a pleated filter has a thin layer of dust on it, its actually more efficient at removing air borne particles.

What are you talking about, are you looking for an argument?
You're right.
The point I was making was that it doesn't matter what quality your filter is, it still needs to be changed at the appropriate time.
You are asserting, "Its not how often you charge filters, its the grade you use!!" this is just bad advice.
Use a good filter sure, I agree., But telling people to get a good one, and you don't need to worry about how often you change it, seriously

Ignore

[Bill George]

For the 18 years I lived here with that furnace, I always used pleated filters, 20x25x4, either Trion Air Bear or Honeywell brands. And I agree that the undersized return didn't cause the issue as the furnace worked for many years with it. It's probably a good bet that dirt/dust build up is the ultimate cause of the high temp errors. I wish I had been able to take a look at the coils, but they went up and out of the house and onto a truck in one motion. With the age of the unit (24 years), it felt like the right time to just change it all out. I don't regret doing it, but maybe I'll do a better job of watching for dust build up with the new system.

Well you upgraded and if you keep using the pleated filters, check and replace when needed it will stay clean plus your going to pay for the upgrade with your savings in gas. My (Trane) has been in since 2007 and I have the lowest heating bills in the area. Also my Honeywell WiFi thermostat lets me adjust and check temperatures while I am gone on vacation or otherwise. It also has a Circulate mode for the fan that cycles the ECM blower motor on low speed from time to time to help keep the temperature the same on both floor levels. I have also left the Fan on in Continuous mode in the summer. I hope I was able to help.

[Bruce Wrenn]

As a part of annual servicing, I remove fan assembly. Blow any dirt out of motor, and wash the blower wheel. Oil the bearings, and reinstall. Original furnace ( a Carrier) lasted 38 years, with the original blower still in it. New Goodmans have ECM motors with ball bearings. As for sizing duct work, the Trane Ductulator is the holy bible. Very few techs have ever seen one. It's just grab a box of flex, and you are a duct work expert. For filters, I prefer the electrostatic ones. Take them out once a month and wash them.

[Jason Roehl]

I strongly suspect that the worst blowers are where lots of aerosols are present—where people use air fresheners, or burn candles or incense, or whatever else. Those tiny droplets can sail right through a filter, but will stick nicely to a blower wheel vane, and then attract dirt, eventually throwing the wheel out of balance.

Probably the best thing that can be done at installation is to oversize the filter housing. This will slow the return air down a great deal, allowing anything in the airstream to more readily settle on the filter.

Next week, I’ll begin the annual changeout of over 230 filters at work…5 air handlers and 200ish fan-coil units…

[Bill George]

Yes my students had a Ductulater ( https://www.amazon.com/Air-Duct-Calculator-Ductulator-Sleeve/dp/B01CYPW0OC/ref=asc_df_B01CYPW0OC?tag=bngsmtphsnus-20&linkCode=df0&hvadid=80608063550918&hvnetw=s&hvqmt=e&hvbmt=be&hvdev=c&hvlocint=&hvlocphy=&hvtargid=pla-4584207589887323&psc=1) from Trane I also taught the ACCA Manual J heat loss/heat gain load calculation required now in a lot of localities. Plus the ACCA Manual D ductwork design, both the paper versions of both and then the Wrightsoft computer programs. We also had a seminar on filter types when to use and when to change. Our students were and are pretty much in demand, most had jobs before graduation.

[Jack Frederick]

Bill, We are downsizing, moving in a couple months. Curious what your view on my proposed change in the hvac side of the new older house. It currently has a 95% furnace and an old R-22 massive condensing unit, so max of 10 seer. I generally don’t like central ducted system as I have found the duct work so poorly done. Couple that with my representing Fujitsu from ‘98-‘11, adding it to the old house and converting our current home to mini-splits. I will likely 86 the whole system, build my solar system as I have done here, zeroing my electric bill and go with a Fujitsu multi. Now however, Fujitsu has a variable speed air handler that can replace the central furnace utilizing the 2, 3 or 4 ton modulating condensing unit and a zone control system for the current ducting. The rub is the existing ductwork. Typical residential ductwork from the ‘80’s, and later, leaks like a sieve and is about impossible to access to repair, and let’s face it is an odious job. I always advise testing for duct leakage before investing in new hvac equipment. If the ducting is shot or so poorly done, abandon it and go with the minis. Again, I did it here and created two closets and storage under the stairs by eliminating the ducting. We have been very happy with the performance and reliability. Funny that the ductulator pops up in discussion now. While packing up some papers I found mine. It is ragged, but still works;)

[Jim Koepke]

It's not a good sign that it was able to get that dirty to start with. Even the old ones in our rental houses, that operated most of their life before we even owned them for years, still look clean. I was surprised that they are.

It has been ~30 years in service and this is likely the first time it has been cleaned. It is actually a pretty light coating of dust compared to others in my experience. Also the filter set up on this system isn't exactly state of the art. It is a heat only system. The Pacific North West wasn't supposed to need air conditioning. Some air can get into the system without passing through the filter. It is not a top notch system, but it works for us.


Learned that lesson. For many years I ran MERV 11s in my HVAC system. Then I decided that MERV 13s must be better so I bought those and installed one. Immediately started having the burners cut out due to high temp. Went back to 11s. However over the last year, those also started causing high temp errors. Moved down to MERV 8s. Worked for a bit, but then started having high temp errors again with the filter in. Worked without the filter. The 3rd service tech finally offered a probable diagnosis of the blower slowly failing, along with an undersized duct on the return air side. …

This is the kind of thing that would have me checking the blower wheel and other areas for being loaded with dust. With less air movement things can get hotter, causing other failure modes.


Thanks for this thread Jim. I never thought of this as something easily checked and corrected.

You are very welcome Stan. That is my reason for posting on this. Hopefully people knowing about this task that an HVAC tech is unwilling to do might save folks some money. In my estimation there would be a charge of at least an hour or two for pulling, cleaning and reassembly. It is a dirty job that few techs are all warm and fuzzy about undertaking. Mine gets placed on my shop bench with my shop vac right in there with the brush. Back in my field service days there was no shop vac available.


I strongly suspect that the worst blowers are where lots of aerosols are present—where people use air fresheners, or burn candles or incense, or whatever else. Those tiny droplets can sail right through a filter, but will stick nicely to a blower wheel vane, and then attract dirt, eventually throwing the wheel out of balance.
…

My wife loves burning fragrant candles. It is doubtful she can be convinced to stop. The other problem might be the access to the furnace is in the washroom where we keep the cat litter box.


FYI when a pleated filter has a thin layer of dust on it, its actually more efficient at removing air borne particles.

The original posting of this seems to have gone missing. Not sure if this was a test of my knowledge when a trainer suggested it or if they thought it was a positive thing.

Yes, a filter with a thin layer of dust is likely to remove more airborne particles while reducing airflow at the same time.

jtk

[Bill George]

Yes a pleated filter with a thin layer of dust is more effective, and before my words get twisted again... thin is the Key word. IF you can still see through the filter its just doing its job. Restriction, sure it adds to the pressure drop but most are using that ECM blower so not an issue. Pleated filters will not pass dirt as the fiber glass when plugged. Filters should be checked and replaced as needed, some with a cleaner house or building will stay clean longer others may need changed monthly or even more often. You also might consider having the ducts professionally cleaned.

The biggest issue with older ductwork is the sizing, most is not done right. Leaking ducts? If you have ductwork in a Un conditioned attic or crawl space and its leaking get it sealed and using something like hard cast it can be done but its so time consuming. If the duct is in the conditioned space, not a big deal. Depending on where you live, zoned heating and cooling using Mini-splits is the way to go, But the indoor coils and blower wheels plug with dirt so fast so be sure to allow for room to clean them and the costs IF you can not do yourself. Better filters? Sure but I have not found ones that will work with the minis.

Zoned with a hi efficiency gas furnace, sure with the varying speed ECM blower and Carrier was selling a wonderful zoning system that involved a little mini computer controlling the whole works.

[Jim Koepke]

Yes a pleated filter with a thin layer of dust is more effective, and before my words get twisted again... thin is the Key word. IF you can still see through the filter its just doing its job. Restriction, sure it adds to the pressure drop but most are using that ECM blower so not an issue.

Not trying to twist any words Bill. One concept to consider is the law of diminishing returns.

My retirement must have been before the widespread use of ECM blowers. All but one of the blowers I have worked on were used on large blue printing machines. All the squirrel cage fans worked on by me have had non-ECM blowers.

jtk

[Bill George]

Not trying to twist any words Bill. One concept to consider is the law of diminishing returns.

My retirement must have been before the widespread use of ECM blowers. All but one of the blowers I have worked on were used on large blue printing machines. All the squirrel cage fans worked on by me have had non-ECM blowers.

jtk

Jim my Free advice comes from experience in the field, when servicing for example Liebert computer room units that was their criteria for replacing the filters. Pleated filters are so effective at cleaning the air, you could if you wanted replace them daily.... its your money. Remember the amperage draw depends on the amount of air measured in CFM moved. ECM motors use ball bearings and are very efficient in the use of energy, I think you would be hard pressed today to buy a non-ECM equipped unit.

[Jim Koepke]

My experience also comes from working in a different field. My reason for posting was to inform others of one problem that can occur with centrifugal fans.

The heating system currently open for work is at least 30 years old. My employment working on blueprint machines and engineering copiers was also about 30 years ago. The fan motors were on when the machines were on. Some of the bigger machines had timers to keep the fans running after it was shut down to have the fans cool the lamps.

The air flow on a blueprint machine also serves to create an air knife for separating the original from the print during the process. When the fan blades became dirty there would usually be problems where the original/print separation took place.

jtk

[Bill George]

Jim I am going to guess you had a lot of corrosion in those units from the ammonia? I've been in some blueprint shops but never needed to work on their AC, but I have worked in a lot of industrial plants on their units, worst was Firestone tire plant with all that lamp black!

[Jim Koepke]

No, the ammonia never got to the fans in my experience. The machines were designed to blown it out through the exhaust.

Earlier in my career one job was running an older blueprint machine that was not vented. One of the worst jobs of my life.

jtk

[Jim Koepke]

Finished up work on the heater yesterday. Good thing to be familiar with reading electrical schematics and being skeptical enough to check my work. No mistakes, but it feels better when turning on the power knowing it isn't going to turn into a smoke and spark test.

Like so many instruction manuals for installing a retrofit kit, this one had a few discrepancies. Most likely parts have changed over the years and the instruction file wasn't updated. Hopefully the breaker replacement kit will serve better than the previous fuse system.

The way the fan is made has the motor mounted inside one half of the centrifugal fan wheel. This made it difficult to clean with my old toothbrush. This was my solution:

492940

The cup brush came from my kit of Dremel tools. The other piece is an aluminum fence tie that was smashed on one end to pick dust out of the corners.

The air flow is slightly improved. One of the floor vents has a piece of paper taped to the wall above it. It rises a couple of inches higher than it did before.

The important part is SWMBO is happy. She sometimes seems almost impressed with my being able to fix something around the house without burning the place down.

jtk

[Bill George]

What I used for cleaning curved vanes was either a 1/4 or 3/8 inch round wire brush for cleaning tube and fittings before soldering. I forgot if you had a AC A coil after the blower but sometimes with a good mirror and flashlight you can inspect the air entering side of it for dirt.

[Jim Koepke]

No AC coil, just a heater element. It was checked for dirt. There was very little to be brushed off of the insulators and metal support structure.

jtk