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Newly installed furnace does not provide enough heat

Posted by wyzhao (My Page) on
Thu, Jan 2, 14 at 1:55

I recently had a contractor install a 3 ton Bryrant 925T (two stage variable speed 95 AFUE ) furnace to replace my original 5 ton carrier 80% efficient furnace for my first floor which is almost 1900 sqft (I have another 5 ton system for my 2nd floor which is more than 1900 sqft.). I double checked with the contractor about the size and the contractor said my old system was oversized which I believe so.

However, the new system does not provide enough air flow. I can only feel air flow within 1 or 2 feet from the vents (I have 10 vents on the first floor). It takes more than one hour to heat the 1st floor. I think I have at least 20% leak in the 1st floor ducts. I cannot do anything about the ducts because they are enclosed between floors.

My contractor told me that the high efficient system takes longer to heat the house, but it seems too long for me. Also the air flow is so weak that heat only accumulate around the vents.

Is what I described normal for a 2 stage variable speed high efficient system or I need a system with bigger size?

Thank you in advance.


Follow-Up Postings:

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RE: Newly installed furnace does not provide enough heat

Location please...

You fail to mention the size of your new furnace. Three ton refers to blower size rating, not BTU output. I will assume it's the 60 K size. Please confirm with complete model number of new furnace.

The 925T furnace is two stage heat with high eff blower but not variable speed. What thermostat was installed? It should be a true two stage model that controls the staging not through a timer on control board that leaves you on high stage whether needed or not. Too many dealers take a shortcut on this issue that cheats both this nice furnace as well as homeowner's comfort and pocketbook.

At this point you have provided a nice anecdotal story with few facts.

Airflow on new furnace can be adjusted within a small range. Dealer should be asked to come out and set it on highest setting to see if that makes a difference.

You should know you don't get the blast of air from the high eff condensing furnaces with high eff blowers that you do from the older non condensing less efficient furnaces with conventional PSC blower motors. As different as nite and day.

The ductwork is a big problem as far as heat loss. I don't believe a larger size would make a big difference. I think the real issue is you making the adjustment to the high eff furnace and its operation.

IMO


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RE: Newly installed furnace does not provide enough heat

Thank you for the feedback.

The exact model number is 925TA60100E21. My location is in the tri-valley area (a suburb of the bay area).

I asked for a variable speed furnace. Is there big difference between variable speed and efficient blower?

The dealer is upgrading me to a 4 ton system today.


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RE: Newly installed furnace does not provide enough heat

That is an oversized furnace for your location with relatively moderate winter climate. FYI, that's a 100 KBTU high eff furnace 95+% efficiency with a 5 ton rated blower. What the heck is your dealer even thinking? What thermostat was installed-important?

You need a load calculation before any exchange is made. And you should be just as interested in BTU output as to blower rating size. What are you doing if anything about AC?

The major negative you lose with the high eff ECM blower motor over high eff var speed blower is not as good dehumidification in AC mode.

And again and I can not emphasize this enough, you need a load calculation performed for heating before any exchange is made. A major mistake if you don't heed this advice.

IMO

This post was edited by tigerdunes on Thu, Jan 2, 14 at 13:52


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RE: Newly installed furnace does not provide enough heat

If he's talking about the SF Bay area, dehumidification isn't an issue.

He hasn't mentioned the warm up temperature rise, but I can add anecdotally that my house takes more than an hour for (say) an 8 degree setback recovery. I find that very acceptable, faster warm-ups require more and hotter air flow that I find harsh and uncomfortable. To each his/her own.


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RE: Newly installed furnace does not provide enough heat

The contractor said that they calculated according to manual J and resulted in a 60K Btu system. However, as I mentioned in the 1st post, I feel it is not big enough. Mainly I think the blower is not powerful enough so the airflow does not reach far enough for my house.

If my ducts have lots of resistance (caused by turns or twists), does it matter for the Btu or blower size?

Please respond quickly if possible.

I think I am ignorant on the issue and I need your opinion. Thank you.


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RE: Newly installed furnace does not provide enough heat

Same thing just happened to us. Our previous furnace was oversized for the house but we bought it and installed ourselves because it was a great deal. Now we have a dealer installed right sized furnace and one upstairs bedroom is colder than we would like. We were so used to the old furnace. The new one is less noticeable.

According to my DH who installed all the ductwork himself there is nothing we can do other than add a secondary heat source to the bedroom. Perhaps he should have installed another vent in the large bedroom. Its not too bad just on some cold nights its a few degrees cooler than we would like. We have a thermometers in different rooms to monitor the temps so we know its a few degree cooler than downstairs.

We are thinking of adding a gas fireplace to the bedroom which we had already planned for before the new furnace.

Hope you can figure it out.


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RE: Newly installed furnace does not provide enough heat

You are totally mistaken and off track.

What if anything are you doing about AC?

What about the thermostat-third time I have asked?

The ductwork is what it is unless you plan on reworking, tearing it out or making modifications. If you have major leaks as you believe, a larger size will just lose more BTUs.

If you are getting good room temperature consistency in all areas of the house, then you are doing fine.

If you are using a large setback at the thermostat, it will take longer to recover with a high eff furnace with a high eff blower. I do not believe in large setbacks unless one plans to be away from their home for an extended period of time.

I would rely on a good load calculation documented in writing for heating with only an average ductwork system for correct sizing.

IMO


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RE: Newly installed furnace does not provide enough heat

If your old furnace was a 120K BTU and 80% efficiency ( I doubt it was that high), then the net output was 96K BTU. Your new furnace is 100K BTU at 95% which translates to a 95K BTU output. The new furnace is about the same size as the old one.

Why did the contractor install a 100K furnace if the load calculation was 60K?

Have you verified the furnace is going into the second (high) stage?

I am going to take a wild guess that you have a inexpensive thermostat which cannot control the two stages and the timer on the board has not been configured properly to go the the second stage.

Don't spend any more money until the contractor explains to you in terms you understand what the problem is and how he is going to resolve it.


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RE: Newly installed furnace does not provide enough heat

The contractor has installed the 100K BTU furnace for me.

The new thermostat is a Emerson, type # 1F80-0261 20-30VAC.

I did not feel the difference between stages. I asked the contractor and he told me that the control logic is in the furnace and any thermostat can work.

This new one furnace has similar airflow as the old one. The contractor told me oversizing won't matter because the first stage is only 40K BTU. Also the blower will adjust the speed according to the stage and static resistance. I also have an intake of size 15" x 30" (open chassis) and the contractor told me it is fine for 100KBTU.

I am suspecting that the case might be as mike_home said. On the other hand, this contractor is an authorized dealer of Bryant and is also in the business for 20 years. I don't think he would make an novice mistake.


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RE: Newly installed furnace does not provide enough heat

"any thermostat will do". Not necessarily true for a 2-stage unit.


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RE: Newly installed furnace does not provide enough heat

Big mistake, so sad.

1F80-0261 Emerson Blue 2" Single Stage Thermostat

oversized furnace, possibly undersized return if that's the only return, and wrong thermostat...

a great example of a dealer looking out for himself not the homeowner...and what's worse is the homeowner allowing it...

IMO

This post was edited by tigerdunes on Fri, Jan 3, 14 at 7:42


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RE: Newly installed furnace does not provide enough heat

" this contractor is an authorized dealer of Bryant and is also in the business for 20 years. I don't think he would make an novice mistake"

Are you sure he is Bryant Factory Authorized Dealer (FAD)? Is he listed on the Bryant web site as a FAD? If yes, then he must provide a 100% satisfaction guarantee. If he cannot make the fixes to your satisfaction he is obligated to remove the equipment and return your money during the first year.

Maybe the business is 20 years old, but this guy is either clueless or just doesn't care what he sells to his customers. I can't believe he has sold you a furnace which is more than twice the size it needs to be and then compounds the problem by installing an inappropriate cheap thermostat with an undersized return. I would bet there are additional installation problems which you don't even know about.


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RE: Newly installed furnace does not provide enough heat

You live in a very moderate climate and that is a really BIG furnace for your sized place. Was the duct work pressure tested as required by CA code? You think you have at least 20% leakage. It could well be more and I think is the root of the problem. The contractors, and your, solution is to throw more equipment at it. CA requires duct repair to reach a 6% maximum duct leakage number at the time of equipment replacement. There are some new internal ductwork spray systems out that are designed to repair a system like yours. I have no experience with them and so cannot comment on how well they work, but the analogy I will use for your system is that you have angina. A good heart that cannot deliver the blood due to arterial blockages. BTW, the duct testing is supposed to be done by a third party so no shenanigans take place. Google "DOE duct leakage"


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RE: Newly installed furnace does not provide enough heat

Thank you all for the feedback and information.

The contractor has tried best to fix my ducts but because they are enclosed, they still have at least 20% leak.

I have a high ceiling and a big living room / family room. The vents are only on the inner side of the rooms so if the airflow is weak, it cannot reach the further corners of the rooms.

When the contractor calculated load, they did not test the resistance of the ducts but I think the duct resistance will affect the strength of the airflow.

I am partly to be blamed because I insisted that the airflow is too weak (probably I have not got used to it). That is the reason I asked for a bigger blower. However, I am not sure whether the weak airflow is due to the single stage thermostat. I don't know with 60K Btu furnace (correct size), I will get enough air flow to .

The contractor is nice in that they swap the furnaces without charging me. Also they have done other jobs well. But I was surprised that the furnace was changed so quickly as I previously asked for 2 weeks' evaluation time. Also I was surprised that the new furnace is 100K Btu, not expected 80K .

Because the furnace is 2 stage, the 1st stage is only 40K Btu, is it correct size for my place? That is the argument of the contractor.


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RE: Newly installed furnace does not provide enough heat

Simple question: for 2 stage furnace, is oversizing still a problem?


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RE: Newly installed furnace does not provide enough heat

Dear Wyzhao: Please read Tigerdunes' posts. The Emerson 1F80-0261 is a SINGLE STAGE THERMOSTAT and is not compatible with your TWO STAGE FURNACE. While contractors frequently do this and set it up to run on second stage only (seems to be a California thing), this is not how the system should be set up. It sounds like the contractor, nice or otherwise, doesn't know what he is doing. Tell him to install a 2 stage thermostat and to wire it according to the installation instructions (not the seat of his pants).


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RE: Newly installed furnace does not provide enough heat

Sometimes 20 years experience really means 1 months experience 240 times.


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RE: Newly installed furnace does not provide enough heat

"I did not feel the difference between stages."

If you can't tell the difference between the two stages then you still have a problem. Either the furnace never changes stages, or your duct work is so bad that a majority of the air is lost before it reaches the registers.

The Bryant 925 100K BTU furnace puts out 63,000 BTU in the low stage, and 97,000 BTU in the high stage. That is a 50% difference in air flow. You should at least hear this when you stand next to the furnace. If you can't call Mr. Bryant with his 20 years of experience back ASAP.

The furnace is sized for the high stage. The low stage is used either to maintain the set point once it is reached and on mild temperature days.

I find it strange this contractor has no problem swapping out your furnace but does not want to install a true 2-stage thermostat.


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