Where does my problem lie? Static pressure readings inside

[signal15]

In an effort to try to pin down where my problem is before I have someone come and redo ductwork, replace parts, or clean; I'm trying to figure out where my problem lies. Not a single HVAC guy I've ever had out to look at the system over the past 4 years has EVER had anything to test static pressure. Not only that, but they all contradicted each other. So, my plan is to track down the problem, and then tell an HVAC guy what needs to be fixed. I'm sick of paying for service calls and making no progress.

When it's over 82 or 83 outside, my AC cannot keep up when I have my indoor temp set to 74. Usually it gets to between 77 an 79, but that's it. It's a Trane XR90 with a 3 ton AC unit. House is 5 years old, 6" walls, thermal camera shows no heat leakage during the winter, even when it's -20F. Living area is approximately 3500 sq ft.

Some of the ductwork was 85 foot runs of that flexible corrugated stuff. I had it all ripped out and replaced with 7" steel pipe. I also had an air return added in an area of the house that I was told needed another one. It did make an improvement in that area of the house, but the AC still cannot keep up.

I noticed that if I take my filter out, it feels like I have triple the airflow. I haven't left it run that way though, for obvious reasons. So my first thought was that the air filter is too restrictive. My differential pressure sensor came today. I have 0.15" of pressure loss across the filter. That doesn't seem unreasonable from what I've read. Static pressure between the blower compartment and right before the AC coil is 0.77", which seems high to me. And pressure loss across the AC coil is 0.39". I'm not sure if the numbers for the AC coil are good or not. I turned off the AC, but left the fan on to see if maybe it was frosting up. Now it's at 0.34" across the coil. There is no access panel to view the coil, and I'm not doing any cutting/ductwork to get at it (someone else can do it).

The cross section of the air return running into the air handler is 252.5 sq in, and the cross section of the supply side is 358 sq in. One of the HVAC guys told me I should have triple the air return area as the supply area. That seems a bit excessive, and I don't trust the fully trust the guys that I've had out. The only guy I trusted stopped doing residential. :(

According to the table in the manual for the furnace, at 0.77" with the fan currently on High, it is pushing around 1200cfm. Another HVAC guy told me you need 400cfm per ton of cooling, which is where it's at now.

Does anyone have any suggestions? Are there any temp readings I should take to better diagnose the issue?

[btuhack]

So, my plan is to track down the problem, and then tell an HVAC guy what needs to be fixed.
You're doomed.

If I had a nickel for every time a customer thought they had a grasp of the situation...

Find a good guy, stick to telling him the symptoms, and let HIM figure out the rest...without looking over his shoulder or asking him "so what do you think" every couple of minutes.

[ComfortablyNumb]

Since this isn't a DIY site, nobody here is going to tell you anything more than you have quite obviously have a problem. It's unfortunate to hear you've not been able to find a professional - Where are you located? I'm sure someone here can point you in the right direction to contact a reputable company in your area.

[ComfortablyNumb]

You're doomed.

If I had a nickel for every time a customer thought they had a grasp of the situation...

Find a good guy, stick to telling him the symptoms, and let HIM figure out the rest...without looking over his shoulder or asking him "so what do you think" every couple of minutes.
Couldn't have said it better. And the thing that really makes it unfortunate is that now that you've had multiple hacks out at your place, that your trust in HVAC technicians has diminished, and it gives us all a bad name who actually want to help you and do the job right. We are out there, I promise.

[signal15]

I'm in the Minneapolis/St. Paul area.

My experience with HVAC guys at this house and my last house have all been disasters except for one company that doesn't do residential anymore.

If you've got recommendations for someone awesome, I'm certainly willing to listen. I'm an engineer, and I can certainly spend the time to suck in information and troubleshoot myself. But to be honest, I really don't want to. I bought the differential pressure gauge because it was half the price of paying for someone to come park in my driveway. I just want someone who knows exactly what he's talking about to come and tell me what's wrong, and fix the problem(s). But, I also want someone that can tell me why it's a problem, other than just saying that some duct looks too small, or something else based on nothing.

[hcong]

In an effort to try to pin down where my problem is before I have someone come and redo ductwork, replace parts, or clean; I'm trying to figure out where my problem lies. Not a single HVAC guy I've ever had out to look at the system over the past 4 years has EVER had anything to test static pressure. Not only that, but they all contradicted each other. So, my plan is to track down the problem, and then tell an HVAC guy what needs to be fixed. I'm sick of paying for service calls and making no progress.

Without seeing your system, I wouldn't be able to tell you much. I would still recommend you find a professional in your area but I'll point out some things that look like it should be checked.


When it's over 82 or 83 outside, my AC cannot keep up when I have my indoor temp set to 74. Usually it gets to between 77 an 79, but that's it. It's a Trane XR90 with a 3 ton AC unit. House is 5 years old, 6" walls, thermal camera shows no heat leakage during the winter, even when it's -20F. Living area is approximately 3500 sq ft.

3 ton AC unit for a 3,500 sq. ft. house seems small, but your house is pretty new. Did the AC use to work for the house before all these problems occurred or has it always been unable to hold 74 F?


Some of the ductwork was 85 foot runs of that flexible corrugated stuff. I had it all ripped out and replaced with 7" steel pipe. I also had an air return added in an area of the house that I was told needed another one. It did make an improvement in that area of the house, but the AC still cannot keep up.

7" steel pipe? I haven't really used steel ducts before but I know that a 3 ton system ideally pushes 1200 cfm and that will require a 16" duct. 7" is closer to 150 cfm.


I noticed that if I take my filter out, it feels like I have triple the airflow. I haven't left it run that way though, for obvious reasons. So my first thought was that the air filter is too restrictive. My differential pressure sensor came today. I have 0.15" of pressure loss across the filter. That doesn't seem unreasonable from what I've read. Static pressure between the blower compartment and right before the AC coil is 0.77", which seems high to me. And pressure loss across the AC coil is 0.39". I'm not sure if the numbers for the AC coil are good or not. I turned off the AC, but left the fan on to see if maybe it was frosting up. Now it's at 0.34" across the coil. There is no access panel to view the coil, and I'm not doing any cutting/ductwork to get at it (someone else can do it).

Yep, keep the filter in to protect the coils. Did you upgrade your filters or change your filters before?


The cross section of the air return running into the air handler is 252.5 sq in, and the cross section of the supply side is 358 sq in. One of the HVAC guys told me I should have triple the air return area as the supply area. That seems a bit excessive, and I don't trust the fully trust the guys that I've had out. The only guy I trusted stopped doing residential. :(

Ducts seem fine for a 3 ton.


According to the table in the manual for the furnace, at 0.77" with the fan currently on High, it is pushing around 1200cfm. Another HVAC guy told me you need 400cfm per ton of cooling, which is where it's at now.

The guy is right, 400 cfm/ton is a good number to use. Your blower measurement and the manual both came out as 0.77"... that is good. Have the AC guy check your air flow at the registers.


Does anyone have any suggestions? Are there any temp readings I should take to better diagnose the issue?

Yes, what temperature is coming out of your supply registers?

Now I am a designer, so I wouldn't be able to tell you what to check for on your equipment, but looking at your system as a whole you might want to have someone do a manual J calculation just to verify the size of the AC. But before you do that, make sure your AC and furnace are working properly.

[BaldLoonie]

As my cousin in KY is finding, hard to find a GOOD contractor.

Static in the supply is lousy. We are finding some evaps are really restrictive. .39 over the coil sounds like a Rheem N coil at 3 ton :( The difference after it sits a while sounds like water on the coil. Then your supply ducts sound rather restrictive too. It should be under .1"

You say .77 in the supply, you have to add the return to get TESP for checking a blower chart.

[second opinion]

0.77 between the blower and before A coil is quite high. Above the blower housing and bellow the coil is the secondary heat exchanger that could be dirty.

[signal15]

3 ton AC unit for a 3,500 sq. ft. house seems small, but your house is pretty new. Did the AC use to work for the house before all these problems occurred or has it always been unable to hold 74 F?

Yes, it worked last year. And I had my summer temp set to 72.




7" steel pipe? I haven't really used steel ducts before but I know that a 3 ton system ideally pushes 1200 cfm and that will require a 16" duct. 7" is closer to 150 cfm.

Sorry, I should elaborate on this. I have large rectangular trunk lines, and the ductwork to the vents running off of that was that flexible insulated stuff. I replaced with 7" round steel/tin ducting, it it has been foamed over because it's in the ceiling of a garage (bedroom above). Another air return was added to that bedroom. The bedroom/master bath has 6 total supplies (4x12) but only had two 6x16 or so returns. HVAC guys doing the ductwork said I needed at least one more return.




Yep, keep the filter in to protect the coils. Did you upgrade your filters or change your filters before?

It had a Honeywell 20x25x4 in it when I moved in. I couldn't find them locally, so I switched to the Filtrete. Then about 3 years ago, I switched to commercial MERV 11's and now MERV 8's. The filter type hasn't changed since I started having this problem.



Yes, what temperature is coming out of your supply registers?


I will test this tonight. One thing I have noticed though is that the vents closest to the furnace blow a LOT more air than vents farther from the furnace. A couple of the bedrooms and one of the bathrooms get colder than the rest of the house. I'm pretty sure the system is NOT balanced at all. In fact, I know it isn't as the damper for one whole section of the house was completely closed when I moved in. The house was brand new, but it was a bank foreclosure on the builder. So it's likely that the original HVAC contractor never finished up their work. In fact, it looks like it's possible that they came in and installed ductwork correctly, but then the bank brought in someone else to finish it up quick and dirty with some flex pipe. Like I said, I've removed and replaced the long runs of flex with tin. But there are still a few shorter runs in there (15 feet or so).

When I asked a couple of the HVAC guys that were out about balancing, they all said that you just feel how much air is coming out of the vents and adjust the dampers to reduce if it's too much. I'm pretty sure that's not the way to do it properly.

Could my AC unit be low on refrigerant? I did notice last night that it seems to be making more noise than usual. I don't think I could hear it in the garage before, but now I can.

When I moved in, there was a 3 ton coil already in the furnace, but no outside unit. The coil is NOT a Trane coil, I can't remember the name/model, but I took a photo of it and have it somewhere. After an $8k and a $12k quote from two different Trane dealers to install just the outside unit, I ended up going with a Coleman unit for $xxxx installed ($xxxx for the unit, $xxx for labor and charging). I know it's not the greatest AC unit in the world, but it worked fine for 3-4 years. I would have gone Trane, but <edited out ripoff price> seems like price gouging to me, and <edited out ripoff price(From Your Opinion>? That's insane. From what I read, a Trane unit should have cost me between <edited> installed depending on the model I went with.

[second opinion]

Yes, it worked last year. And I had my summer temp set to 72.





Sorry, I should elaborate on this. I have large rectangular trunk lines, and the ductwork to the vents running off of that was that flexible insulated stuff. I replaced with 7" round steel/tin ducting, it it has been foamed over because it's in the ceiling of a garage (bedroom above). Another air return was added to that bedroom. The bedroom/master bath has 6 total supplies (4x12) but only had two 6x16 or so returns. HVAC guys doing the ductwork said I needed at least one more return.





It had a Honeywell 20x25x4 in it when I moved in. I couldn't find them locally, so I switched to the Filtrete. Then about 3 years ago, I switched to commercial MERV 11's and now MERV 8's. The filter type hasn't changed since I started having this problem.




I will test this tonight. One thing I have noticed though is that the vents closest to the furnace blow a LOT more air than vents farther from the furnace. A couple of the bedrooms and one of the bathrooms get colder than the rest of the house. I'm pretty sure the system is NOT balanced at all. In fact, I know it isn't as the damper for one whole section of the house was completely closed when I moved in. The house was brand new, but it was a bank foreclosure on the builder. So it's likely that the original HVAC contractor never finished up their work. In fact, it looks like it's possible that they came in and installed ductwork correctly, but then the bank brought in someone else to finish it up quick and dirty with some flex pipe. Like I said, I've removed and replaced the long runs of flex with tin. But there are still a few shorter runs in there (15 feet or so).

When I asked a couple of the HVAC guys that were out about balancing, they all said that you just feel how much air is coming out of the vents and adjust the dampers to reduce if it's too much. I'm pretty sure that's not the way to do it properly.

Could my AC unit be low on refrigerant? I did notice last night that it seems to be making more noise than usual. I don't think I could hear it in the garage before, but now I can.

When I moved in, there was a 3 ton coil already in the furnace, but no outside unit. The coil is NOT a Trane coil, I can't remember the name/model, but I took a photo of it and have it somewhere. After an $8k and a $12k quote from two different Trane dealers to install just the outside unit, I ended up going with a Coleman unit for $xxxx installed ($xxxx for the unit, $xxx for labor and charging). I know it's not the greatest AC unit in the world, but it worked fine for 3-4 years. I would have gone Trane, but $xxxx seems like price gouging to me, and $xxk? That's insane. From what I read, a Trane unit should have cost me between $xk and $xxxx installed depending on the model I went with.

If your unit was cooling and the only change was flex to metal, it should be better.

your pressure drop across the secondary heat exchanger is excessive.

Have the unit serviced and have them document pressures, temperatures, with superheat, sub-cooling and airflow cfm.

And edit your pricing from your post, it is against the rules.

Try the dealer locator and post your geographical area for us.


Don't post pricing and DON"T quote posts with pricing!!!

[signal15]

Try the dealer locator and post your geographical area for us.

I'm in the Minneapolis/St. Paul area. I'm reluctant to ever call another Trane dealer. The pricing I got from the two I mentioned above was way out of line, and a 3rd one told me over the phone, with no info and without even looking at the system that to install central air, I would need to install a Trane zoning system as well, which would be several thousand dollars more.

It's too bad, I think Trane makes good stuff. But the Trane people I've dealt with here were all telling me I needed to spend *ridiculous* amounts of money to get AC installed.

There are 6 Trane dealers within 20 miles of me. I don't remember which ones I spoke with, and a 4th one is the company that installed the unit. They won't help me at all because they didn't get paid when the bank foreclosed on the builder. They finally got paid via a lien, but they were complete a-holes to me when I gave them my address. It wasn't me that screwed them.

[signal15]

I should point out that every one of these guys thinks a Manual J, Manual D, etc are a waste of time and you can calculate everything based on rule of thumb.

The only reason I'm sitting here taking my own measurements and trying to do this stuff is because I haven't found any contractors that want to do it for me. I just want this stuff to work. I know there are problems, and I can make some guesses as to what they are. But ultimately, I don't want to play armchair HVAC guy.

I just called another company today to ask if I could get someone out to have the unit serviced and have them document pressures, temperatures, with superheat, sub-cooling and airflow cfm. (as "second opinion" recommended above). And they were instantly very unexcited, and told me they didn't have the time for all of that.

Am I the only one having problems finding HVAC guys that don't just slap something in based on a rule of thumb?

[genduct]

According to the table in the manual for the furnace, at 0.77" with the fan currently on High, it is pushing around 1200cfm. Another HVAC guy told me you need 400cfm per ton of cooling, which is where it's at now.


True BUT NOT TRUE. You have your max pressure with NO FLOW so the "table info" is misleading. You need to know what amp draw to expect when that many pounds of air is being "shoveled" through the duct.
You have a manometer, what are the real readings?

Are you really seeing a .4 pressure drop over the coil? That sounds high
What is the supply and return pressures on the house side of the coil and filter AKA availiable external static

I understand why you wanted to take your own readings and the typical Tech's lack of understanding of what make the air "squirt" out the little holes.

My contact info9tele #)n profile If you would like to speak

Best, Mike

[comfortdoc]

You need to start at the beginning before anything will make sense. What type of engineering do you do? It is a newer home, see if there are plans available from the building department and verify everything you can see matches the plans. Did the problems start before the ducts were changed or after? What else was done at that time?

Do you know any mechanical engineers that will design the system based on the house.

[signal15]

True BUT NOT TRUE. You have your max pressure with NO FLOW so the "table info" is misleading. You need to know what amp draw to expect when that many pounds of air is being "shoveled" through the duct.
You have a manometer, what are the real readings?

Are you really seeing a .4 pressure drop over the coil? That sounds high
What is the supply and return pressures on the house side of the coil and filter AKA availiable external static

I understand why you wanted to take your own readings and the typical Tech's lack of understanding of what make the air "squirt" out the little holes.

My contact info9tele #)n profile If you would like to speak

Best, Mike

I was going to put them in from memory, but I don't remember all of the values off the top of my head. I will retake the readings tonight at each point and post them.

So the "available external static" is the difference between a point right before the filter (dirty side) and after the A-coil?

[tipsrfine]

As long as nothing has changed to the home or the system between when it kept set temp and now that it is not, I would suspect loss of charge or problem with metering device. If it happened from one to summer to the next, I would tend not to suspect a dirty evap or secondary heat exchanger, but it nevertheless could be that.

[signal15]

Ok, measurements...

Temp at a vent closest to furnace: 60.3F
Temp at a vent on the far south of the house: 65.5F
Temp at a vent in the bedroom over garage: 64.3F
Temp right after AC coil: 58.8F
Temp of return air: 77.5F

Pressure before filter (dirty side): -0.24
Pressure in blower compartment: -0.37
Pressure before A-coil: 0.41"
Pressure after A-coil: Fluctuates from 0.07" to 0.15"

Looks like the pressure drop across the coil is less than it was yesterday. I'm getting roughly a 19 degree drop over the coil, is this normal? Can these numbers justify me having someone out to cut an access hole and look at the heat exchanger and coil to see if they are clogged up with something?

Again, I know the system is not even remotely close to balanced. The vent closest the furnace whistles and blows a ton of air, and the vents farther away have a very weak airflow. I don't have anything to measure air speed, but, can I use the manometer to take pressure readings at the vents? Would that be useful at all?

[tipsrfine]

Send me an e-mail. I have something I can send you; probably too DIY to post here.

[signal15]

That's a great idea. I think my local power company will recommend people also.

Sent from my Galaxy Nexus using Tapatalk 2

[signal15]

I found a local guy that was recommended by NCI. After speaking with him on the phone, I feel really comfortable that he'll be able to help me out. He is coming out Tuesday.

Thanks for everyone's help.

Sent from my Galaxy Nexus using Tapatalk 2

[catmanacman]

With a mere 18 degree temp split leeds me to beleive you are moving clse to enough air take out the filter and install a blue cheepo and see if helps

[signal15]

Thanks to NCI, I found a guy 5 mins from me that is NCI and NATE certified. He confirmed my readings. It's an ADC coil, and the pressure drop should be 0.19". The blower is filled with crap, so the coil probably is also. Looks like the builder ran without a filter during construction.

He is coming out next week to clean it, and then balance the system. He's also running the calcs to make sure the ducting is sufficient.

Nice to have someone out that isn't flying by the seat of their pants.

Sent from my Galaxy Nexus using Tapatalk 2

[udarrell]

Thanks to NCI, I found a guy 5 mins from me that is NCI and NATE certified. He confirmed my readings. It's an ADC coil, and the pressure drop should be 0.19". The blower is filled with crap, so the coil probably is also. Looks like the builder ran without a filter during construction.

He is coming out next week to clean it, and then balance the system. He's also running the calcs to make sure the ducting is sufficient.

Nice to have someone out that isn't flying by the seat of their pants.

Sent from my Galaxy Nexus using Tapatalk 2
Well finally, that is real good news; everyone you call ought to be close to his level of knowledge & competence.

I hope he has an anemometer with him to check the airflow CFM from the Supply-Air diffusers. The airflow system needs to be properly balanced.

Since airflow increased tremendously when you removed the filter; was that with the blower door open too?

Hopefully he will check for adequate filter area sizing & everything concerning the Return-Air system. Performing a manual D on the duct system might be helpful.

The blower & blower wheel blades will have to be thoroughly cleaned; don't move or knock-off the wheel's balancing weights...

[signal15]

I can't remember if the increased airflow was with the filter door in or out. I see where you are coming from though. It is likely I don't have sufficient return flow. I only have 2 returns for the kitchen, dining room, great room and hallway, which is a pretty large area volume wise.

Sent from my Galaxy Nexus using Tapatalk 2

[udarrell]

I can't remember if the increased airflow was with the filter door in or out. I see where you are coming from though. It is likely I don't have sufficient return flow. I only have 2 returns for the kitchen, dining room, great room and hallway, which is a pretty large area volume wise. Sent from my Galaxy Nexus using Tapatalk 2

For many years the blower door has to be closed so it depresses a switch allowing power to the motor, therefore, it was probably with just the filter removed.

It might considerably improve airflow if you would have large filter grilles installed in the conditioned areas & not use any in the furnace. It is impossible to have too much filter area...the more the better.

[beenthere]

PCHVAC, this is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise here. Please apply to the AOPC today, thank you.

You can find the rules for posting and qualifications here (http://hvac-talk.com/vbb/showthread.php?t=957002).

Your post has been deleted.
Further infractions may result in loss of posting privileges.

[grasshopper]

I'm in the Minneapolis/St. Paul area.

My experience with HVAC guys at this house and my last house have all been disasters except for one company that doesn't do residential anymore.

If you've got recommendations for someone awesome, I'm certainly willing to listen. I'm an engineer, and I can certainly spend the time to suck in information and troubleshoot myself. But to be honest, I really don't want to. I bought the differential pressure gauge because it was half the price of paying for someone to come park in my driveway. I just want someone who knows exactly what he's talking about to come and tell me what's wrong, and fix the problem(s). But, I also want someone that can tell me why it's a problem, other than just saying that some duct looks too small, or something else based on nothing.

Im not in the cities much anymore.... closer to St. Cloud now. But contact me and we can talk, if you need help still.