Hello,

We recently moved into this home. The system has 4 zones, gas force air with central air that is original to the home so 20 years.

I have a few questions maybe someone can assist with.

1. I was walking checking the returns to see if i could feel they were drawing air in. I couldn't tell by feeling. Is this normal and if so, is there another way to confirm they are working? What triggered this was we turned the fireplace on on the main level and the upstairs was hot so was hoping it was pulling that back into the system and recirculating.
2. I noticed when looking at the furnace where the returns come into the system it is like a cardboard type material that seems to form the box for the return. is that normal? There were some 1/8" gaps between it so not sure if that is making it less efficient.
3. It seems that if i turn the fan on in one zone the fan comes full on at the furnace. It seems if that is the case i should just as well have it working on all zones?
4. If the above is accurate, is there a way to control all zones from a single location?

Thanks for the help.

 

1. Normal to not feel return flow. Use a piece of 8 1/2 x 11 paper to check.
2. Need to call someone it to fix the gaps. It is common to see cheap installations.
3. Recommend having multi-stage system so fan can run at lower speed when not all zones calling. May be setup wrong.
4. Not with normal thermostats. Some higher end ones will let you.

 

If the system was installed as a heating system and then upgraded to A/C....... the second floor return(s) will be low and will not draw the hot air from the ceiling.

You can hold a candle in front of a return to see if it's drawing air in.

It sounds like your system probably uses air bypass to maintain flow vs variable speed blower. Converting to static pressure controlled variable speed could be very costly.

 

A proper return duct/grille combo should operate around 500 FPM grille face velocity, should be sensed by holding your hand close to the grille.

If you'd like to get into it, please advise:
1. Nearest large city.
2. Size of home.
3. Make & M/N of furnace, coil and AC.
4. Images of furnace and attached ductwork, especially the "cardboard".
5. Make of Zone control system (There's usually a separate "Zone Control Panel" mounted near the furnace).

There should be a "Bypass Damper" to maintain constant airflow through the furnace/coil when not all zones call, and a Discharge Sensor is usually required. Hopefully, the images will show whether those devices are provided.

This'll be a good one!

 

Thanks for the reply. Here are some pictures maybe that will help and give some clarity as maybe it isn't a big deal either and all is well. It is different than my previous newer home.

1. Fargo, ND
2. 5500 sq feet. (2nd level, main level and basement)
3. Furnace Trane 90 XE, A/C is an Amana ANX130481AC
4. Below
5. Last image

Let me know if you need further clarity or pictures of anything and hoping i got the images you need below.

I really want to learn more about the system and be sure it is running optimally as I understand the importance. I knew my old house pretty well but no next to nothing about this.

------------------------------------------------

In the image below starting left to right. I see these 2 pipes and they go from the return to ducting. Guessing this is in the event hat all dampers are closed in the system but somehow the fan is on perhaps that it doesn't strain the system?

The light, I haven't tried pulling this cardboard looking stuff away from it but strange the light is within the return isn't it?

Furthest to the right. This looks to be a vent directly to outside and dumping cold air into the room. This seems strange to me. Is this right?


Here are some examples of the seems that seem a bit large to me that maybe need taping? Also, another example and view of the cardboard stuff i mention.


Picture of the system as a whole


Maybe a better shot of the main returns and vent lines


I believe the below is the zone control system?

 

I added an arrow in your third picture illustrating the bypass damper in your system.
That lever will move as the static pressure changes in the ductwork.

Not strange...... wrong. I'd definitely look into that.

Looks like a lot of sloppy connections. Do you feel air coming out of them ?
Any air filters in the system ? None seen in the pictures.

 

"Sloppy" is too generous, I'm sorry I asked!.

Is the "Cardboard" "Thermopan"? If so, it's permitted for RETURN ducts only. All of the return ducts in the room containing the furnace must be sealed airtight, to prevent circulating combustion products to the living space - Even with "Sealed Combustion" or "Direct Vent" (Call it what you will) as we see here. That includes the 1/8" gaps you identified. The open duct is for the combustion air supply, assuming the "XE" is permitted for "single pipe" installation. Many 90+ furnaces are "two pipe" only, with the air intake connected to the furnace.

The furnace model number would help, but with a 4 ton ("...48...") AC, it's gotta be 100 MBH or more. Fargo, ND: Cool design 88FDB/70FWB - 13F and 18 grains of moisture. Heat Design -17F as in BRRR! Definitely a heating climate. Design airflow should be 1,600 to 1,800 CFM in your dry climate, and I see nothing to indicate your airflow could be anywhere near that (Return "drop" to furnace should be at least 30x12 or equivalent at Manual D 700 FPM max, for example). With your climate, the cooling should be no more than 3 tons, so one more case of gross oversizing of cooling accompanied by substandard airflow.

Trol-A-Temp appears to have been bought by Honeywell in 1999. In any event, a barometric bypass damper such as shown in your image 3 should have the damper arm sloping about 45 degrees to the right when closed, rotating CCW to about horizontal in the full open position and should move freely when you push on the counterweight. IE: It's improperly adjusted as shown. It appears to be 6" to 8" in size, undersized even with two equally sized zones. You need a 10" or 12" damper for your 4 zone, 4 ton system.

I'm guessing the filter is at the furnace return connection, with a too short transition at the cabinet. Filter area should be 700-800 sq. in. so it's probably undersized. And the Code-required means to assure uniform airflow across the filter are not provided.

You might want to (have someone?) check inside the return duct upstream of the filter for signs of moisture accumulation and/or mold growth: The humidifier bypass duct terminates in turbulent airflow, so there may be condensation when/if the humidifier operates.

Did I mention the Manual D required balancing dampers do not appear to be provided at the supply branches?

The furnace M/N would be nice to have, access it by removing the louvered front panel, I think. And you might want to look inside the blower compartment (solid front panel) to see if there're any contaminants on the clean air side of the filter. Filter size and type would also be good to know.

FYI: Trane may require returns at both sides of the furnace.

Like I said - "A good one"! To learn from, that is.

As always, none of these comments are to reflect on the many knowledgeable, highly trained HVAC contractors and techs out there, may their tribe increase!

 

Hi, is this return sealed?



Geo🇺🇸

 

Thanks again for the help here and suggestion. Trane Furnace Model: TUC100C960B7

Is the cardboard thermopan: Yes I believe it is.

EDIT: Sorry I didn't see Geochruchis post. That is where the Filter is and it is pressure fit and being sucked into place by the furnace it feels. I don't feel air moving from it but difficult to tell. I think i should try the candle trick maybe. I have tried the paper check but it didn't do much so either i am doing it wrong or there is just not enough air movement that it does anything.

Few follow up questions

1. To check on the light do you guys think I pull that cardboard(thermopan) down? If so I am guessing I run the risk then of disassembling the main return venting that is in place?
2. In the first image the two pipes to the left. If I am understanding you ferd42 the pipe with the damper should be much larger.(10-12”) Could these be subsidizing that do you think?
3. A two pipe furnace with a pipe coming in for fresh air and an exhaust if this furnace can do that is it of value to have that installed vs pulling air from the home like it is current?

I am wondering what you guys would suggest here to get this right and have it function well and last another 20 years?

With the suggestions do you think I will see savings that justify the fixes? The system is 20 years old now. Not sure how long these things go for and what will happen if it needs replacing. I want to be sure I am spending the money on the right things vs saying live with it until it dies (if it dies) and then fix it for example. If there are some quick wins I can do myself great but hvac is a bit new for me diy wise. I am also not opposed to hiring someone if out of my realm.

 

Good News: The furnace venting is "One Pipe", so the open inlet is the right thing to do. And the duct's probably big enough, considering it's permissible to draw some air from the space containing the furnace.

TUC100C960B7: One more case of an undertrained designer specifying too much cooling (4 tons vs. 3 or less) and a furnace with a larger cooling airflow capability (5 tons) than required for the oversized cooling. The furnace requires at least 1,320 CFM (93,000 BTU output at 65F max. temp. rise), and it's shipped set for HI cooling and ML heating airflows (Black and yellow leads). A knowledgeable startup tech should have reduced the cooling speed to ML, but I'd be very surprised to learn that happened. Nor would I be surprised to learn the system isn't delivering that much air now, and the furnace is "cycling on high limit". That the filter's "being sucked into place by the furnace" is a clue.

The light is the least of concerns here: Your first priority is to increase the return air capacity. If possible, add a large round return duct to the LH side of the furnace, to include filter, and terminate it at a new grille in another room close to the furnace. I've often used floor grilles, they work quite well, the trick being to provide a "receptacle" to catch dirt. Think metal box in the floor with the grille in it - here's the trick - with the return duct connected to the side of the box. The grille can be removable for cleaning the box, or you could provide a duct access door in another side of the box. I cleaned the ones in my Rehoboth home every 3 or 4 months, no prob. 14x14 grille and 10" or 12" duct, do include a balancing damper, because there may be some air noise. 16x25 air filter w/ 12" deep plenum. Do this BEFORE you start sealing return ducts, because sealing the ducts will increase resistance to flow, thereby reducing flow.

If the additional return is impractical, you'll have to deal with the mess on the RH side. Let us know. FYI: Trane only requires one side to have a return, but connecting to the unused side is my first choice for a quick fix that works.

As always, none of these comments are to reflect on the many knowledgeable, highly trained HVAC contractors and techs out there, may their tribe increase!


Please clarify "Could these be subsidizing that do you think?", I'm not sure what you mean.

 

Thanks for the reply.

To be sure I am understanding. Do you think that the returns are stifling the system?

Below is an image is my understanding of what you are saying. Am I understanding correctly? This would be an additional return that is 12” with a larger grill. I would place this in the living room since so close. In addition, during the winter months it could draw in heat generated by the fireplace. Am I on the right track with your thought?

Hoping you can help clear up the idea for me.

If better and my understanding correct, there is also an open room on the far left of the picture too.

 

"stifling" - FOR SURE: The "drop" (vertical duct) is too small. its fittings restrictive, and the 20" high filter transition to the 14" high furnace opening is too short. Then there's the mess at the ceiling.

Your diagram shows what I called "RH" (right hand) side of furnace. Do not connect a duct to that side without an extensive rework of what's there. I'd hoped there was sufficient space at what I called the "LH" (left hand) side of the furnace for the new duct. Please tell us about that.

Furnace blowers have two inlets, one of which is partially blocked by the blower motor. The installation I'm currently looking at has the motor on the right. If yours is the same, connecting the new duct to the LH side will help with that restriction too.

Please clarify "Could these be subsidizing that do you think?", I'm not sure what you mean.

 

ok I think I am starting to follow a bit more. To be sure I am on the same page let me try and explain my understanding. It sounds like the potential exists to install the return ducting on both sides of the furnace and you were suggesting adding additional ducting to the LH side. This would be adding a filter and a vent to pull additional air in from the basement hopefully increasing the flow from other vents around the home. You were suggesting the LH side as the RH side would require a lot of additional rework that you were trying to avoid. Am i getting close?

Also, if this helps, the humidifier system has never been used the previous owner said. We also do not intend to use it at this time.

Below is about the best picture I can get of the area and the systems. The LH side is the water heater and main water line. The RH is the softener but could be moved as it isn’t fixed to the ground I believe. I can try and get a wider view of the ceiling too or even do a panorama if that would help. The wall that these items sit against is the living room. The far left wall is to more of a play room area.

Please clarify "Could these be subsidizing that do you think?", I'm not sure what you mean.

What I meant by this was that I noticed there were 2 ducts going from the return ducting the side where the air was conditioned which seems like it would be a circle to me. I wasn’t sure if this was a technique used to aid the return for example when not enough put in or where to small. I don’t understand why those are there is what I was meaning.

 

My suggestion won't work without moving the water heater. That's probably a good thing, because we'll fix that mess at the RH side instead. Please give me some measurements:
1. Size of return drop (vertical duct).
2. Distance between drop and supply plenum on top of cooling coil (this number will be the same as the length of the bypass duct).

Also, please tell us what size and type of filter's installed (or enclose an image of it). I'll develop a sketch showing how to fix it and where to connect the new 12".

Once that's corrected, do remove the humidifier, as that type robs conditioned air from the living space.

As for the two supply ducts you mentioned, it looks like they go through the return duct and continue out the other side, please verify.

 

Looking at your latest image, I realized the bypass connects to the (field-provided) cooling coil enclosure. This is a case of "The more you look, the more you see", in inspection-ese. We'll fix that as part of the humidifier portion of the work.

You might want to check out Honeywell's CPRD bypass damper, to replace the barometric type that's there now.

 

The barometric bypass you are referring you would replace the portion in the images marked bypass with the Honeywell's CPRD bypass damper is that right? What does this do and would you say it is sized correctly?

As for the two supply ducts you mentioned, it looks like they go through the return duct and continue out the other side, please verify.

No they do not look to go through. I can take a close up picture if you like too?

Below are some measurements of the return ducting. Some are not spot on but I would say all are within at least a quarter inch. Is this what you needed?

 

Here's the first priority: A new 20x25 return plenum w/ 20x25 media air cleaner (similar Honeywell F100 MERV11). Although I've shown the new 12" on the side, it can be connected anywhere on the new plenum. IE: DO NOT connect the new duct to the existing vertical duct.

With the 2x4 trusses, you'll only be able to install a 12" wide floor grille (Don't cut the truss chords!), so use a 14x14 wall grille for the 12" duct if there's a wall, or use a 24x12 floor grille, connected through two 10" ducts. Whatever you decide, the new grille must be exposed to the main living space and not be separated from the main area by a door.

 

You'll need to solidly support the new plenum from the floor so there's no stress on the furnace cabinet. Scrap the existing filter, etc.

 

I don't think you would be giving guidance if not something a diyer couldn't do. I have only really installed an air exchanger years ago.

The new plenum (is that what it is called. The replacement metal box that will attach to the vertical piece and where the filter is housed) is that something I would build or can i buy this piece at a home center? I think the 20x25 piece is the MAC. Not sure what a MAC is but it looks like a replacement for the air filter that is in the current configuration? Is this what it is? (20x25 MAC?)

Last, the circle you have in the bottom right. Is that a return vent into the living area behind the furnace?

Really appreciate the suggestions. I am curious doing this piece, do you think I will be able to start noticing the returns working better after this? (i understand this is part 1)

Below is the estimated dimensions of that new return plenum(i will call it that for now unless it is something else and I am corrected)

 

You'll at least need to find a local sheet metal shop to fabricate the new plenum. Give the guy the MAC, the sketch and the dimensions of the furnace opening, and he should be able to take it from there. While you're at it, make sure the furnace opening is full size - it's field cut to indentations on the side of the cabinet and I've seen jobs where the installer cut the opening smaller than the indentations. And if you're not comfortable with that, find an HVAC contractor to do the whole job (He'll probably want to sell you a UV light, and who knows what else, good luck).

Like I said, the new return duct ("Vent" is a word that describes fuel burning, making plumbing drains work, etc.) can be connected anywhere to the plenum, but try keep a few inches away from the MAC. In fact, connecting it to the end of the plenum would be best, if possible, after seeing the 30.5". On dimensions, you haven't listed the most important, the width of the "drop": We know it's 25+" in the side not shown, so we need the side that is shown. FYI: 16" is the required dimension, it'll be interesting to see the actual (10"???). AND we might want to address that now.

You will see an improvement at the grilles when it's all done, probably see some after Phase I.

 

What is the best way to find the true furnace opening dimensions and what its potential could be if made smaller?

You are correct it looks to be 10"

The mac. What is a mac and for this furnace which would you recommend?

 

MAC = Media Air Cleaner

Ferd42 listed Honeywell F100 MERV11 or something similar.

https://www.supplyhouse.com/Honeywel...-x-25-2000-cfm

Interesting thread to read.....

 

Thanks for the link and pointing that out. I am doing a lot of cramming with the help I am getting to try and be sure I can be somewhat part of the conversation.

What does the MAC do different then the filter I have in the system today?

ferd42 it seems as well that the vertical width is 10" as you suspected. It sounded like if this might be the case we might need to visit something here too?

 

Furnace opening: Remove the blower door (bottom panel), look for the indentations and compare with existing opening. Measure existing opening and check that it's a true rectangle. You could also check the product data and possibly the Installation Instructions. A smaller opening than manufacturer specs will restrict flow.

I don't know anything about your existing filter aside from its size, so I can't answer. The F100 is a manufactured product I routinely spec, and it does not permit air to bypass the filter (as do a lot of contractor jury rigs). The longer transition will expose the entire filter surface, not just some portion of the filter as is now the case.

Yep, replace the 10x25 drop with 16x25 now. (HVAC Insiders: Existing is sized at 0.10" instead of recommended 600 FPM).

 

I checked the Trane specs. Return opening should be 14-7/8" x 23-3/4".

 

Thanks again for the response. It is going to be a week likely before I can locate someone to build this. I also have a hvac guy coming to look at it and waiting his call to give me a quote. I will respond back as soon as I have some additional details.

I will check the measurements. In the mean time below is a picture for reference. Looks like it consumes the full space.

 

Looks like the blower motor is on the right side. And you have a pleated filter, depending on thickness and MERV could have much more resistance to flow than the F100. You must have some air bypassing the filter, because there's no "safing" at the bottom (can't see top or sides too well) to prevent that.

 

And you might want to remove the blue tape from the blower door switch. Forgive me if you put it there, but it's not the kind of thing a knowledgeable tech would do.

 

Nope I didn't put that tape there. I will get rid of it. What is "safing"? What info do you need to see if the filter is being bypassed?

 

Safing is a piece of metal along the top, sides and bottom that the filter seats against to prevent air flowing around (bypassing) the filter, is usually installed on both sides of the filter. Not to worry about that now if you're going with the MAC.

I've been thinking about the last phase - Correcting the Thermopan, which should be coordinated with installing the new ducts we've been discussing.

Joist bays are limited to 400 CFM, or one ton of AC capacity. Whoever installed your system tried to squeeze four times that through there, and the fix will be relatively easy. I think it's there because there are one or two stud spaces in the wall above being used for return air from the living space. Two would be perfect for the joist bay, since stud spaces are limited to 200 CFM each.

What you'll need to do is remove the Thermopan and check for air handling stud spaces above. If there are stud spaces used for air, check that they're fully cut out at the floor penetration and remove any subfloor or plate (horizontal 2x4 at the base of the wall) blocking the full width of the stud space. FYI: I've seen jobs where there were return grilles in walls, but the floor openings had not been cut (Sad but true), and you'll want to check for grilles above (that includes the 2nd floor) if there are no holes in the floor. Removing the Thermopan will also reveal whether supply ducts pass through the Thermopan; if so, they'll have to be rerouted.

Putting it back together, move all the smaller return ducts from the Thermopan onto the horizontal metal duct beneath the Thermopan - or better yet, onto the new drop. And you'll need to check the other ends of the smaller ducts for stud spaces, etc.

When it's all back together, buy some UL181 duct sealant and have a ball sealing all those gaps.

Do not seal anything now, since that'll further restrict airflow! Wait until your furnace can "breathe better".

 

Thanks for the reply.

Let me see if i am following. Are you suggesting to remove some of the thermopan to see if there is a hole to the upstairs possibly 2 floors that might be used as a return cavity right?

I have not yet found anyone to do the metal work yet. Should i wait to do this until I have someone found to do that? It is getting cold here and we are using the heat daily now sadly.

 

Right.

Yes, this needs to be coordinated with the first phase, so you'll have to wait.

In the interim, you might want to check the air temperature rise ("ATR") across the furnace when it's heating. Drill two holes, one above the cooling coil and one just before the filter (there may be holes now, check it out - perhaps the black rectangle?) and measure air temps inside the ducts. ATR is the difference between the two. If you're able to do that, tell us your readings.

 

Checked your specs: Furnace output is 93 MBH and permitted ATR is 35F to 65F. It'll be interesting to see the actual ATR. AND that'll also tell us the approxroximate heating airflow, another interesting number. AND we'll then be able to estimate cooling airflow, ditto.

 

Rethinking this, just drill holes around where the red dots are shown, forget the black. You'll need a thermometer that goes from 160F to 140F or so, digital types are best.

 

That should be "60F to..."

 

I had a guy come over for 2 reasons yesterday this issue being the main one to see if he could build out the box for the return. Second was to service the furnace i have today. I tried explaining what I could on what you mention and he said the limit is with the opening from the furnace to the return. Even if made bigger it will not pull any more air is what he thought. He was suggesting to put a whole new furnace in or lifting the one we have to put a return box on the bottom as well. This furnace runs without issue now so I don't want to spend the money on that until I am replacing parts. He thought the same but didn't have any other suggestions on the return which made me wonder a bit. He also did a few other things as part of the service.

1. He plugged (with a towel for now) the humidifier unit since it hasn't been used nor do i know how to work it nor do i think i need it current. This is to see if it aids in the return
2. He pulled the cold air return pipe down so he could create a trap to limit the amount of air coming into that room. This did seem to help a bit. His other suggestion was to place a damper controlled by the furnace on this pipe to start/stop the air as needed but suggested to see how this works.
3. The damper weight he moved to the bottom as even off it never looked like that damper moved. He didn't think this would do much but might aid in returns. This next part didn't make much sense to me unless he was just talking through things to determine the problem. He said to close that off as he noticed when he pulled the tungsten ignitor that it looked like it might be getting to hot and could be from the damper recirculating that hot air. But if this damper doesn't open not sure how that is happening.

I will keep looking for someone to build out this box but I have a feeling this is going to be tuff out here. I might churn through hvac guys before I get one that will just do it. I live 30 min outside of Fargo so to pull them over here I am paying even for quotes. I will keep looking.

I will go get a digital thermometer to get you some readings in those holes too. I still need to do that.

Any thoughts on the above?

 

The furnace manufacturer is OK with a single side return for 4 tons, so raising the unit to install a plenum base - a good but costly idea - is not necessary.

There are some contractors and techs out there who don't understand airflow - may they see the error of their ways and learn. Troubleshooting airflow problems - something those guys don't understand - is identical to troubleshooting refrigerant circuits - something they have to understand to be permitted to handle refrigerants: Measure pressures (albeit hugely lower pressures and using different instruments): If he understood airflow, he would have used a manometer to measure "Head Pressure" at the coil outlet and "Suction Pressure" at the filter inlet. I'm guessing he did neither. Furthermore, he could have measured pressure along the return duct and drop to troubleshoot restrictions.

Forgive me for "Over Complicating" my previous instructions about the "Drop". Just construct a 36" long 20x25 box, attach it to the MAC/Transition, support it from the floor, insulate it to R6 and connect two pieces of 14" R6 flex duct from the top to the existing metal duct above, no need for the "Drop" to be rectangular metal. You'll still need to get into the Thermopan, etc.

The motorized damper on the combustion air inlet is permitted and a good idea. Just make sure there's an "End Switch" or other fail-safe mechanism on the damper so the furnace won't fire unless the damper's open. There are several combustion equipment manufacturers who offer the product.

As always, these comments are not to reflect on the many knowledgeable contractors and techs out there, may their tribe increase.

 

Nope he didn't measure anything in there you are correct.

To verify what you are saying. In the image with you drawing was that the size of the plenum 20x25x36? I am a little confused where you mean to connect up the 2 14" insulated pipes? Also, if i have these 2 14" pipes would i leave the 10" vertical drop in place? Hoping you can clarify a bit here.

 

Yes the new plenum will be 20"x25" to match the MAC and 36" long to accommodate the THREE ducts (the new return and the two flexible ducts). It'll be a lot easier for the shop to fabricate, too.

Lose the existing 10" drop, and replace it with the two 14" flexible ducts. Won't be real pretty, but it'll work fine.
https://www.amazon.com/Master-Flow-I...4131169&sr=8-2

You'll have to patch the opening where the 10" wide drop connects to the existing horizontal duct that runs below the joists.

 

Quick update on this. i am having a hard time finding someone to do this work. the two i have been able to have over both wanted to sell me a new furnace. The furnace and all works without issue so am not yet interested in that large expense until really needed.

I have had a few other minor things happening and I think i just found out what that might have been caused from. this is a 4 zone system like i have mentioned and I think one of the main zones that comes in the morning damper motor was broken and not opening and possibly tripping the heat sensor within the system to not turn on the furnace or causing it to cycle off.

Anyway. I will update as soon as I find someone. Another thought, i have never done this work myself is that possible here?