2700sf? What is foundation size? 900?

Based on info provided and If I understand correctly, you have a 2700 sq ft home that includes a finished basement living area? Basement area is below grade? What is est living area on main floor, second floor, and basement?

If above is correct, no I don't believe you are undersized. I think something else is causing your issue. First off, you should verify that high stage on furnace is operational. May involve a service call from installing dealer.

IMO

Cavell: the basement/foundation is probably ~700 sq feet. Basement/foundation wall is 1/2 below grade

Tigerdunes:

That is correct. ~1000 sq feet of living space each on the 1st floor and 2nd floor (bedrooms)

The installing dealer/serviceman took a look at the furnace earlier today; verified it was working properly. He cleaned pressure switch hoses and flame sensor to be sure. Tested system operation and seemed to be working properly. 2nd stage fired up immediately when the spread between the desired temp and air temp was >5 F

We only have this problem when the outside temperature drops significantly.

Thanks for your responses and Happy NY.

If problem continues at lower temps, you need a different tech. Thermostat should be checked for correct wiring. You should not be having this problem.

I will assume ductwork has been checked for any major leakage.

Document in writing all conditions in and out if this occurs again. Outside temp,Inside temp, thermostat setting, time of day. Does furnace run continuously when inside temp starts to drop?

IMO

Thermostat was checked and is wired accurately.

Duct work doesn't have any major leakage, but every technician has said our ducts are undersized/should have been bigger.

The furnace was running constantly, and thermostat never reached desired temperature when this malfunction was happening.

Thanks for the advice.

need another tech....

I would contact installing dealer.

Your situation not acceptable.

IMO

This post was edited by tigerdunes on Thu, Jan 1, 15 at 12:19

The new furnace should easily heat the house even with the outside temperature is below 15 degrees.

Everything you have said so far leads me to believe the furnace is only operating in the low stage. Can you hear the difference in the blower speed when you go from low to high stage? If it does go to the high stage, do you feel a difference in temperature at the vent? Perhaps the blower speed is changing but the gas valve is still stuck on the low stage.

I am a new member,but a fascinated reader for a # of years.I have a question for the more knowledgeable members of this forum:
125 000 BTU @ 78%=97 500 BTU,
80 000 BTU @ 96%=76 800 BTU.
If only the furnace was changed and now it seems to be insufficient,does the reduction of 20 700 BTU play in as part of the problem?Or is it only theoretical math?
Hope someone is able to help DanChiTown !!!

Furnace has been holding temperature steady all day. However, significantly warmer outside today vs when we encountered the problem.

Yes, second stage is noticeably working...confirmed by technician yesterday as well.

Big test will be in a few days when we get hit with another cold spell here in Chicago....

Thanks for the replies.

Confirmed by technician?

Yea, right.

Is this tech from installing company?

If he can not find the problem and says everything checks out, then what is his explanation for the falling inside temperature during cold snaps?

IMO

This post was edited by tigerdunes on Fri, Jan 2, 15 at 7:56

125 000 BTU @ 78%=97 500 BTU
80 000 BTU @ 96%=76 800 BTU

These calculations are correct. The input BTUs are never exactly the stated nominal values, but they are close enough.

The OP stated the living space is 2000 sq. feet with a 700 sq. foot basement. If that is true, then the original furnace was over sized. An 80K BTU furnace should be able to heat the home to 72 degrees down to a temperature of 10 degrees. If it can't then there may be a serious insulation or supply problem.

Did you verify the model number of the furnace? It may not be an 80K BTU furnace.

Tigerdunes:
It was a tech from the installing company. Upon arrival, he too believed the furnace was not kicking into 2nd stage.

He cleaned the pressure switch hoses and flame sensor. Then showed me the flames kicking into 2nd stage when the hood was off the furnace and we had the thermostat calling for >5 F vs inside temperature. (I am clearly a novice, and could be something else he should've explained to me). He thinks the sensor was the issue but didn't find anything 'wrong.'

Mike_Home:
I did verify the model number and serial number of furnace to be 80k BTU's. Unless the installers slapped a homemade sticker on the furnace, then I could have been "taken" here.

Very skeptical on everything right now...

Originally didn't even want a 2 stage furnace b/c it sounded like more parts and issues that could go wrong...didn't really care if it was 1-3 degrees colder/warmer in parts of my house...

You are getting nowhere with your installing dealer. I suppose you just plan on living with this situation? Get a 2nd opinion from another Carrier dealer. Obviously the question of competence with your installer comes to mind.

IMO

Is the installer a Bryant Factory Authorized Dealer? If he is, then there is an obligation to fix the problem or take the furnace out and refund your money.

tigerdunes:
roger that

mike_home:
yes, largest in Illinois. They will exchange the furnace for a new one if not satisfied.

furnace is working well for last 48 hours...just heard the furnace kick into high stage when my wife jacked the temp +3F ...still worth a second opinion.

You need to do a heat-loss calculation; if necessary get others to help you.
http://www.loadcalc.net/
If you apply yourself or get help from others, the Calc should NOT be difficult.

Chicago County winter design with calc shows 2ðF; I'd use at least zero. See what you get...

You can use the snipping tool & upload the calc numbers for us to review. Do it...

Here is a link that might be useful: Whole House heat-loss & Heat-Gain calc

I see nothing wrong with OP performing his own load calc. According to climate data, the low end of average winter lows for Chicago is around 20 degrees. Normally one sizes furnaces for the average. However, anyone familiar with this location knows that there can be much lower blasts of cold air. If OP intends to run the heating load calc, I would use 10 degrees as the design temp for winter low, a compromise to the extremes which I think is wrong to use.

IMO

The winter design temperature listed in the Energy Star Outdoor Design Condition Manual for Chicago County is 2 degrees F. But the average low in January is stated as 18F and a record low of -25F. The OP has already seen temperatures below 15F and we are barely into the winter season. The Chicago area has wide variations of temperatures. It would be best to do the calculations for a few temperatures and analyze the results.

X2 with Mike.

It would be interesting though to learn how low 76 KBTUs takes you. Assuming the 80 K furnace was actually installed, I still believe the problem is dealer nstall related.

TD

I'll get that load calc done soon.

I did have 5 estimates back in October; although no load calculation done every option included an 80k BTU high 95+ efficient furnace. Still worth seeing the "real results"

Had yet another technician out this morning. Saw the problem happening. He found the PVC pipe pulling air into the furnace from outside had froze over. Popped an additional air supply hole from inside the machine. Said the furnace was not receiving enough air and was short cycling (for lack of a better term).

Furnace has been running smoothly since. Though took about 5 hrs to heat the house 13 degrees...was 1F outside last night with a windchill of -18F. Currently 3F outside my house right now (noon ish)...

Thank you to all for the posts.

Inside air? Reusing waste air for combustion? That's a no no. And will only cause you serious and expensive trouble down the road. Please clarify. Installing dealer should be called back to correct any issue regarding fresh air required for combustion.

Thermostat is now maintaining temp setting at 3 deg outside temp?

IMO

Tigerdunes:

I attached a picture to better explain the situation.

The intake PVC pipe is still in place and not detached. The screen inside of it keeps freezing over when downwind from the exhaust PVC pipe next to it. (top picture attached). It looks like the screen holes are too small, therefore collecting ice easier and/ or it needs to be angled down further (bottom left picture).

The technician took a round already stamped piece of metal off of the side of the furnace. (bottom right picture) He said this will take air from the furnace room and keep the furnace running if/when the pipe freezes over again.

Yes, thermostat is working with outside temp at 3F and holding inside temperature at the moment; but has taken 5+ hours to regain 13F inside.

Thanks again.

The screens are not needed and should be removed. I don't have screens on my PVC pipes and have never had a problem with ice forming.

How far are the PVC pipes from the ground? You want to be above a bad snow fall so they will not be blocked.

You are using air from inside the house. This may be a problem if there is not enough oxygen in the house to sustain complete combustion. I don't have a high opinion of this installer based on what has transpired so far.

Mike_Home:
I am removing the screen now. Was thinking about adding a small piece of PVC to aim the pipe towards the ground. Create more of an angle, thus creating less opportunity for frost to form.

PVC pipes are approximately 4.5 feet above the ground

Shall I have the installer come back, reseal the hole in the furnace after the screens and additional PVC piece is added? Furnace room has about 250 sq feet in there.

Trust me, if I could go back in time I would never use this company. One of the biggest Bryant dealers in the country...yeah well...want to blast their name here in this blog and tell everyone to stay away...

I don't like what this 2nd dealer/tech did on the combustion air. It may solve your issue on the BTU output but may cause premature corrosion and failure on heat exchanger down the road.

I would not accept this solution.

I think the wire mesh is inconsequential. Usually to prevent small animals.

Your original installing dealer needs to be called out and straighten out this issue of venting and fresh air required for good combustion.

IMO

The intake pipe should point downward. The exhaust pipe should point horizontally and away from the house. The distance between the two opening must be at least 12 inches.

The installed mesh openings are too small in my opinion. I could see how snow and ice could build up and cut down the air flow.

After our near record breaking week of cold here, I am going to have the installing dealer extend the intake to point further down and put the cap/piece of metal back on the furnace to prevent corrosion or longer term issues.

The two openings are >12 inches apart.

I removed the wire in the meantime, it kept catching blowing snow as well.

Although running near constantly (which I believe these high efficiency furnaces should be in this type of cold) furnace has been holding a comfortable 70F for near 36 hrs...thanks again for the help.

I live in the Chicago area and just had a new HE furnace installed. I have 2600 sq above ground and had a 100k btu installed. No problems. I was concerned about animals with the vents, but our installer told us they should not be a problem. He did not recommend adding any mesh.