what kind of filter are you using? sounds like restrictive filter and undersized duct issues.

 

It's a Lennox version with a 20x20x5" filter.

 

Post full model number of the furnace. Sounds like an over sized furnace. Or under sized duct work.

 

Trying to find it. Would it be under the cover?

 

My home is 2600 sqft with ducting in the crawlspace and also in the attic. I've checked, nothing seems collapsed or restricted. Contractor came out yesterday, he checked and couldn't find any restrictions. He ordered a new sensor and left it running with the filter out. It runs fine like that.

 

He should have checked heat rise in second stage, along with static pressure of your duct system while it was running in second stage.

 

Model# EL296DF070XV48B-04

I know the contractor said he slightly upsized the blower from the previous unit. The previous unit didn't seem to blow very hard at all.

 

I will have to ask if those are things he checked. What is 'heat rise'? Also, if it turns out to be slightly oversized, wouldn't it just be a matter of turning down the max blower CFM in the settings? It's currently set at 1275 which is the default.

 

Heat rise. the difference in temp between the entering air and the leaving air at the furnace.

Slow the blower too much and the temp rise becomes too high, and locks out on limit. So you have no heat.

 

OK, I watched some youtube vids on those two tests. Makes sense. Anyone know why the fancy pants iComfort thermostat wouldn't show me the E311 code on it without having to remove the panel on the furnace and check it there?

 

Still having issues. I am not getting results with the contractor who I paid over $ to install this system. They sent out their 'best' tech, who did seem at least intelligent, and he said maybe it's the sensor. I'm not sure what the sensor is sensing that is throwing this alarm, whether it be the burners overheating or the air volume is too low. Would anyone know the answer to that question? Today their less than stellar tech showed up, replaced the sensor and said everything was great. I get home, the air filter is still laying there next to the furnace, of course it's still working great you idiot. I talked to the owner of the company a couple days ago and he said that if the sensor didn't fix it then there was a problem with my ductwork and sounded like I was SOL. My question is, isn't the contractor responsible for sizing the equipment properly and setting it up to work? Why would I just be SOL because my ductwork is undersized? I have 3 returns to the stinking furnace, hard to believe it's not getting enough air. I am almost regretting buying a Lennox product already and being held hostage by my contractor and Lennox who won't answer any of my questions over the phone. There's barely any posts at all online when I google this issue, it's like I'm the only one that owns this furnace. I asked my contractor to do a heat rise test and a static pressure. He agreed to the heat rise though he hasn't done it but refused to do the static test for free as it was 'very extensive'. I'm really getting irritated. What should my next move be?

 

Over heating and low air flow go hand in hand. Checking total external static pressure (TESP) takes 2 minutes or less. If it runs fine with no filter I'd guess you're lacking enough duct for the furnace blower motor to ramp up with a filter in place.

 

How does the furnace figure out it's not getting enough flow? The filter is a 20x20x4". The return trunk then has an 8x16" rectangular duct and a 12" round leaving it. The rectangular goes to two floor returns and the 12" round goes to a ceiling return on the second floor.

 

A static test would take less then 10 minutes(including drilling the holes for a first time test).

Your 8X16 is good for much over 800CFM, without going to a high static.

 

Confused by your statement. I have an 8x16 AND a 12" round coming off the trunk for the return. So you're saying the 8x16 is good for 800CFM but what about the 12" with it? Again, the furnace is trying to push 1275 CFM. And actually the AC is set to 1600CFM.

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Can someone tell me HOW the furnace knows it's not getting enough CFM? How does it detect this?

 

The furnace merely responds according to the physics of the situation. If it gets too hot, sensors can detect that to shut it down.

Does that answer your question?

 

Not really, I'm asking for specifics. I don't think it's detecting overheating since when I turn the blower up over 1275 it kicks it down to stage 1 even faster. That would tell me that it must be checking CFM or static pressure somehow.

 

Don’t blame Lennox for a poor contractor.
Also stop messing with something you know little about. Contact Lennox and get another contractor.

 

It's my furnace, I bought it. I paid $ for it. I can do what I please with it. If I was scared to mess with things I know little about I wouldn't know how to do anything. Because I'm not afraid to learn I've done all my own automotive repairs on numerous vehicles, transmissions, engine swaps, rebuilt an engine in a Ferrari 355 just to name a few. I work in automation, dealt with 100+ industrial robots all networked together via dozens of PLC controllers to weld truck cabs for Toyota. An iComfort thermostat with a furnace is not beyond my capability of comprehension. I didn't blame Lennox for a poor contractor, I think it's ridiculous they won't answer my questions for a product I own. I understand they want to talk to someone who is supposedly licensed and capable, but so far the only capable person looking at my furnace has been myself. For having 3 weeks of experience I don't think I'm doing half bad. Calling another contractor would mean more $$$ out of my pocket for something that should be working for the $$$ I already paid.

If you're going to give responses like that, I don't know why you're on this forum.

 

Sounds to me like you've found your problem if leaving the large pleated filter out will enable system to operate. You need to increase the return air flow by simply adding another large return, or switch to a less restrictive air filter. Either way you simply need less restriction therefore more air flow. :cheers:

 

Post pics of the way the duct is attached to the furnace, and the way the smaller duct is attached to your 16X20 drop.

 

?

 

Only pic I had on hand. It shows how they taped the filter box to the top of the furnace and the trunk attached to that. I wouldn't say it looks exactly professional. Would you? The box reaches up to the ceiling where it ends. The 12" round goes through the ceiling and into the attic. The 8x16 comes off between the box and the wall and goes down along the wall to the crawlspace.

 

View attachment 469461

Only pic I had on hand. It shows how they taped the filter box to the top of the furnace and the trunk attached to that. I wouldn't say it looks exactly professional. Would you? The box reaches up to the ceiling where it ends. The 12" round goes through the ceiling and into the attic. The 8x16 comes off between the box and the wall and goes down along the wall to the crawlspace.

Blocking off a 1/3 of your filter is your problem, along with those 3m filters.

 

That looks horrendous.


The future isn't what it use to be.

 

Be nice to see the attachment of the other ducts to that plenum.

But you got a return problem. Supply may be just as bad.

 

You can't see the connections from the outside really, covered in insulation and hidden in the ceiling. Taking the cover off the air filter I shot a pic up from the inside and you can see the connections. I ran the AC tonight, it runs up to 1600CFM which is right for a 4 ton unit (x400CFM per ton) It actually stays running at 1600 but it does flash an E312 which is not enough CFM for cooling mode. Even with the filter door off and wide open it still gets that error, may mean that it's now having problems with the supply side or possibly the mechanism for sensing flow is just overly sensitive? I wish I really understood how it determines these errors. My contractor insists that a total external static pressure test wouldn't tell him anything. He's supposed to come Friday morning. I'll post up the pics I took tomorrow morning.

 

If a TESP doesn't tell him anything. Then he doesn't understand static pressure, or duct work.

A simple supply check and a return check will tell which or if both ducts are under sized. He can do it in cooling mode when the blower is trying to move 1600 CFM. Your TESP is probably well over 1.2" in cooling mode, and still not moving 1600CFM.

The blower motor and control board are communicating with each other. And the motor is unable to reach the torque value it has to to move the higher CFMs. Its not overly sensitive, your duct work is under sized/incorrect for the equipment size you have.

 

Pics

 

First pic is looking up inside the return from the filter box. Second pic, can't really see much but the box goes to the ceiling, the 12" round goes through the sheetrock and the 8x16 goes to the right and back down the wall to the floor. Third picture, sorry about the rotation, just overall pic of installation.