Author Topic: A Carrier TP6 80k BTU furnace's fan  (Read 784 times)

Offline Sergroum

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A Carrier TP6 80k BTU furnace's fan
« on: February 06, 2017, 01:37:25 AM »
Heya.

So a client of mine had this furnace installed recently. In reality he could've more then easily made do with a 60k BTU, but ... he went for an 80,000.

The furnace works fine, but he finds it to be too noisy. Whistling sound on the return and so on. Delta T is pretty low, so if I managed to somehow lower the CFM, it would do alright. But ... how would I be able to lower that CFM, does anyone have any idea? It's a variable speed motor, controlled by dip switches. And the only options that I can see available is comfort/effeciency (default comfort) and low heat rise (default off).  So the blower is already at the lowest speed fan setting, if I understand correctly.  I'm tempted to put this furnace in a perpetual 1st stage. But the problem wont go away during air conditioning. 2 ton AC for ... 1400 CFM.   

If I understand correctly, the TP6 60k BTU furnace would have a 1200 max cfm blower. While an 80k, would have 1600 max cfm.   Is it possible to put a blower from a 60 into 80?  Obviously, the best solution is to change the furnace. The company that installed it clearly oversized it. But they oversized it due to severe insistence of the client himself. Oooph.

Offline walker

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Re: A Carrier TP6 80k BTU furnace's fan
« Reply #1 on: February 06, 2017, 07:18:12 PM »
why would you have 1400CFM for  2 Ton A/C, you'd only need 800CFM

Offline walker

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Re: A Carrier TP6 80k BTU furnace's fan
« Reply #2 on: February 06, 2017, 07:43:20 PM »
I would being doing a total static pressure test on the system.  Sounds to me like the return is undersized.

Offline walker

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Re: A Carrier TP6 80k BTU furnace's fan
« Reply #3 on: February 06, 2017, 07:49:54 PM »
Haven't run in to a TP6 lately, but If I remember correctly the TP5 you can just switch the blower taps on that ECM motor to whatever speed you need based on your ESP, there should be a chart in the installation manual showing the taps and expected CFM based on your ESP

Offline Sergroum

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Re: A Carrier TP6 80k BTU furnace's fan
« Reply #4 on: February 06, 2017, 10:49:11 PM »
When you say blower taps. Do you mean on the board, or somewhere in the module of the blower fan? If it's on the board, then no. on TP6, there are no taps like that. That's the main problem.


The matter is not that I need 1400 cfm on 2 ton. I dont need to. I'd love to lower it. I just ... cant seem to find a way to do it. There are no low/mid/mid-high/high/etc taps on the board. The control is in dip switches, but I fail to find a way to raise, or lower the cfm of the blower, besides the simple stuff. Such as switching between 350/400 setting, or turning high temp rise off/on, or setting comfort/efficiency setting on.

Unless I'm missing something horribly obvious.

Offline walker

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Re: A Carrier TP6 80k BTU furnace's fan
« Reply #5 on: February 06, 2017, 11:26:11 PM »
Other than setting the heat low heat rise to off and to comfort, you can't adjust the heating air flow. You can absolutely set the cooling air flow though.

Is the furnace noisy with the blower door off?  What kind of filter is being used? Are any return air ducts being restricted?

Offline Sergroum

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Re: A Carrier TP6 80k BTU furnace's fan
« Reply #6 on: February 07, 2017, 02:50:42 PM »
The client is hearing a whistling noise from return grills upstairs.  That house could've adequately had a 60k BTU, but the Client insisted on 80.  It wasnt our company who installed it, but he had a disagreement with them and called us? Something of that nature.

Yeah. Apologies. Definitely a way to select CFM for AC. It's the heating that's got me stumped. No obvious restrictions for the return grills. And I guess yes, I imagine adding an extra return downstairs could alleviate the issue. I was just stumped by the whole lack of a way to control CFM for the heating part.

Offline Admin

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Re: A Carrier TP6 80k BTU furnace's fan
« Reply #7 on: February 07, 2017, 04:18:39 PM »
Try Walker's suggestion first.  Make sure dip switch SW1-4 is ON to decrease low heat airflow by approximately 7 percent and high heat by approximately 10 percent for maximum comfort.  Make sure dip switch SW1-3 is OFF.  See the attached chart below.

Are you using a single stage thermostat and letting the furnace board control the staging?  I believe the low fire runs at 50,000 BTU's and the high fire runs at 78,000 BTU's.  You could try locking the furnace into low fire.

Turn SW1-2 ON at the furnace control to lock the furnace into low fire.  The furnace will think you have a 2 stage thermostat, and will expect a signal on W2 to energize high fire.  Just wire the thermostat W to W1 on the furnace and the furnace will run at 50,000 BTU's using lower heating fan speeds.

Try installing a more restrictive pleated filter to reduce return air noise.  Verify the temperature rise.  Or try changing the angle on the louvres on the metal cold air return grill.  If you pitch some of the louvres up, and allow more air to enter, you should be able to reduce the noise.  Otherwise look at adding return air.  Usually the basement is the easiest place to do that.

Offline Sergroum

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Re: A Carrier TP6 80k BTU furnace's fan
« Reply #8 on: February 08, 2017, 01:49:57 PM »
It's set to default. So Comfort setting and low heat rise is turned off.  Which is what 1-3, 1-4 dip switches control.  Adjusting the grill louvres is an interesting idea. Current grill does not allow it, but I can change it and see how it'll go. The noise definitely dissapears when I take the grill off entirely.  If I can put on with adjustable louvres and change the angle, I think this will be the best solution.

If that wont work, it's either a return air in the basement, or locking it to first stage.  I'll just have to confirm that the AC will have 800 cfm on first stage. Which I think it's going to.

Offline Porcupinepuffer

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Re: A Carrier TP6 80k BTU furnace's fan
« Reply #9 on: February 08, 2017, 03:29:06 PM »
If there is no return in the basement, he should have one installed.