Help with Oversized Modulating Furnace

[AGreen0]

Hi HVAC-Talk community,

I have to admit that I am very new to this area and through some recent research have realized how little I understood about your area of expertise but I'm hoping to harness your knowledge to help me provide some suggestions with my contractor who is struggling to solve my heating issues. Here is the situation:

Four years ago I had a York YP9C080B12MP12C modulating furnace installed in my attic to cover the 2 bedrooms up there and the 4 small bedrooms on my second floor (and a TM9M060B12MP12 installed in my basement to cover basement and first floor) as part of a changeover from a broken steam system to forced air. The installer did all the duct work and installed a Source1 (non-communicating) wifi thermostats.

From day 1 we could never get the heat right on the top 2 floors. It's always been the "blows hot and then gets cold" story you hear about forced hot air, but my house was built in 1917 and has very poor insulation (we tried to have blown-in insulation added through the whole house as well as a variety of other energy saving efforts as part of a home energy audit) so I just thought it was the downside of forced air.

When we had our first kid and started sleeping with her bedroom door closed, I noticed that her room got dangerously hot very quickly but the temperature at the thermostat was very delayed in reaching the desired temp. The thermostat is on the hallway landing and there is a return in the ceiling above it but no heat feeds in that area so figured that was the problem.

Recently we had a second kid and now when we close his bedroom door, the problem is made even worse so I tried to get in touch with my previous contractor, but he has gone out of business and the installer is MIA as well. I decided to call another HVAC specialist that a friend recommended and he has been working with me for the past few months but we've not made much progress.

The new HVAC specialist took measurements and said:
- The unit is oversized for the space. (My house is about 2200 sq ft including the basement I think)
- The ductwork is insufficient and the stat was measured an external static pressure of 4.044 (manufacturer recommends .5)
- My thermostat was not capable of maximizing the effectiveness of my furnace

With that in mind, he added additional returns/ductwork to the bedrooms and installed a York communicating thermostat, but the problem has not improved and maybe has gotten worse. The thermostat is showing that the furnace operates at 35% for a while which feels quite comfortable but eventually (after a few cycles usually), it starts to ramp and eventually goes up to 100% which raises the temp in the bedrooms from 67 to 82+ in about 5 minutes, which is really scary with an infant in the bedroom.

Based on a lot of the posts I've read, I recognize that I'm missing a lot of the technical details that you often ask for, but I'm wondering if it's possible to provide any additional suggestions of what we might be able to do to help improve the situation. I saw somewhere that maybe the gas valve wasn't set up correctly or there could be an issue there, but are there any other ideas that I could pass along to my contractor to help?

Appreciate any guidance and happy to provide any additional detail that would be useful.

Thank you!

[CEAS-AC-TECH]

Sounds like you could benifit from some jumper ducts in each room leading to the hall. Also dampers in the duct to balance the system. These will help a bit. Heres a vid of what im speaking of.

https://youtu.be/AyKUUx09iCk

Sent from my LG-G710 using Tapatalk

[kdean1]

Individual rooms overheating when the doors are closed indicates air is not circulating through them. The duct system needs to be revised and balanced.
And it may be that the furnace is too big.
Did the contractor perform a load calculation? Any method other than Manual J is an approximation. Too often a short cut based on floor area is used, with poor results.

The static pressure you report (4.04") cannot be right.

[Juan Madera]

Return air in the bedrooms as well as a supply? Or one return air for each system.

If returns in the rooms, closing the door is unbalancing a improperly designed dust system that is creating a lesser pressure zone in that room.

If one central return, It is hard to imagine the room getting hot with limited circulation (door closed)...

And yes, sounds oversized for the task. A/C on these as well?

[mgenius33]

Does your thermostat have the option of remote sensors to help average the temperature of several different rooms?

Holy cow! You have a total of 140Mbtuh input heat for a 2200 sqft. home??? The 80Mbtuh should handle the whole house no problem.

If your home is that unstable, it would be best to air seal and insulate better instead of throwing larger equipment at it.

[AGreen0]

Individual rooms overheating when the doors are closed indicates air is not circulating through them. The duct system needs to be revised and balanced.
And it may be that the furnace is too big.
Did the contractor perform a load calculation? Any method other than Manual J is an approximation. Too often a short cut based on floor area is used, with poor results.

The static pressure you report (4.04") cannot be right.

I have a feeling that the original contractor did not do a load calculation...they were a subcontractor of a larger renovation project and seemed pretty down-and-dirty.

I'm obviously out of my depth, but the new contractor I'm working with said this:
"Tested the system the pressure on the system is astronomical. To help give you some reference the manufacture wants an external static pressure to be 0.5. The external pressure I measured was 4.044! That is with me opening all the vents."

[AGreen0]

We initially had just the one return in the hall where the thermostat is, but my new contractor added return ducts in 2 out of the 3 bedrooms (the kids' rooms) to help. There are a number of returns on the first floor and it's generally pretty comfortable (a bit drafty but I think that's the house more than the HVAC).

That said, those rooms were getting really hot before we added the returns, so I don't think the limited circulation was preventing the furnace from cranking too much heat into the rooms.

Yes, we have two A/Cs as well and the A/C has been pretty good from what I can tell.

[mgenius33]

I have a feeling that the original contractor did not do a load calculation...they were a subcontractor of a larger renovation project and seemed pretty down-and-dirty.

I'm obviously out of my depth, but the new contractor I'm working with said this:
"Tested the system the pressure on the system is astronomical. To help give you some reference the manufacture wants an external static pressure to be 0.5. The external pressure I measured was 4.044! That is with me opening all the vents."

I don't think the blower motor is capable of that kind of pressure. The variable speed blower motor would likely reach it's rpm limiter well before 2.0" wc.

[AGreen0]

Does your thermostat have the option of remote sensors to help average the temperature of several different rooms?

Holy cow! You have a total of 140Mbtuh input heat for a 2200 sqft. home??? The 80Mbtuh should handle the whole house no problem.

If your home is that unstable, it would be best to air seal and insulate better instead of throwing larger equipment at it.

Great question about the remote sensors. I asked a similar question of our contractor and he's looking into it. Either remote sensors or the ability to move the thermostat into my bedroom...or to add a heat supply in the hallway so at least the thermostat experiences similar heating to the bedrooms.

In general, I feel like there should be some way to tell the furnace "never go to 100%" but I can't seem to figure out how to do that (contractor says not possible).

Funny you should mention it: I actually hired a company (I think I'm not supposed to out them, right? They're out of business now anyway...) to do a home energy audit and then they recommended blown-in insulation throughout the house and some other air seal work. We did it all and then when we did some work recently and opened up the walls, there was maybe 1 foot of insulation in the wall cavity. I had heard stories of people getting fleeced in this way but I trusted this company based on a lot of reviews on Angie's List and they totally scammed me. Now I have holes/cracked shingles all over my house and there's still no insulation.

[mgenius33]

Great question about the remote sensors. I asked a similar question of our contractor and he's looking into it. Either remote sensors or the ability to move the thermostat into my bedroom...or to add a heat supply in the hallway so at least the thermostat experiences similar heating to the bedrooms.

In general, I feel like there should be some way to tell the furnace "never go to 100%" but I can't seem to figure out how to do that (contractor says not possible).

I'm not familiar with your thermostat, but most will have adjustments for more or less aggressive recovery.

[AGreen0]

I'm not familiar with your thermostat, but most will have adjustments for more or less aggressive recovery.

Any idea how that might be labeled if I poked around in the settings? Is it usually called "recovery" or something else? I did see something about firing rate "100%" when I went into the installer settings but was too nervous to mess with it so left it at that setting.

[mgenius33]

Any idea how that might be labeled if I poked around in the settings? Is it usually called "recovery" or something else? I did see something about firing rate "100%" when I went into the installer settings but was too nervous to mess with it so left it at that setting.

I would have to see the manual. There's so many different thermostats out there today, and some manufacturers have firmware updates as well.

[mgenius33]

.

[pacnw]

Any idea how that might be labeled if I poked around in the settings? Is it usually called "recovery" or something else? I did see something about firing rate "100%" when I went into the installer settings but was too nervous to mess with it so left it at that setting.

Did you give model of thermostat?

Another option may be to use a different stat, with remote sensor capability, that can limit the ability of the furnace.
I am not familiar with York so this may not be possible.

You really do need a system evaluation, plan and then make decisions.

That attic furnace is probably the right size for the ENTIRE house!! Proper load and duct calculations will determine this.

[AGreen0]

I would have to see the manual. There's so many different thermostats out there today, and some manufacturers have firmware updates as well.

Here is a link to the manual but I can't see anything about recovery or how I might be able to adjust this: http://www.upgnet.com/PdfFileRedirec...UUM-A-0114.PDF

If I put the fan in "manual" and set it to 35%, does that mean the furnace will limit itself to 35% output?

Last night I tried closing the registers almost all the way shut in the kids' rooms and closing their doors as if they were sleeping and the furnace ramped to 100% and the rooms still got too hot, so struck out there.

It also seems like my thermostat (https://www.york.com/for-your-home/t...cating-control) might not be compatible with remote temperature sensors. Any way to know for sure?

Thanks again for everyone's help...this has already been really helpful and I appreciate the way this community tries to assist in so many different ways.

[pacnw]

Here is a link to the manual but I can't see anything about recovery or how I might be able to adjust this: http://www.upgnet.com/PdfFileRedirec...UUM-A-0114.PDF

If I put the fan in "manual" and set it to 35%, does that mean the furnace will limit itself to 35% output?

Fan refers to the blower only, usually as I am unfamiliar with York specifically. This would NOT limit the firing rate.

[mgenius33]

This thermostat offers 3 stage, stage-up differential temperature settings , and stage up timer. The timer is likely set on. It can be turned off.
You can also “inhibit” the upstaging via a timer as well. This timer will not allow upstaging by the stage up differential.
This thermostat can also allow for down staging. On/off, and a stage down inhibit timer.

You may need to have your installer go through these settings with you, and set them to your preference.