# how to increase a furnace fan speed



## aumanpj (Jul 15, 2009)

I have an Ultra 2 gas fired high efficiency furnace with AC. I want to increase the fan speed. I have been reading online and am not sure what I must do. Attached is a photo of my fan limit control. Is this what I use to increase the fan speed? If so, how should I change it?

I read this: http://www.doityourself.com/stry/adjusting-furnace-fan-speed but I do not see any jumpers they refer to. 

Basically, I am a new home owner having lived in my new home since April of last year. I was quite impressed by the air flow of our new home and how quickly the home could change temperature. Last August we had a new control panel put in and I think the technician may have changed the settings. The unit just isn't blowing like I remember it.

I'd appreciate any input you could provide. Thank you.


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## beenthere (Oct 11, 2008)

The fan limit doesn't control fan speed. There should be another relay. probably in the blower compartment. With the blower motor wires connected to it.

Look in there, and post a pic of it if you can.


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## aumanpj (Jul 15, 2009)

Is this the blower compartment?


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## aumanpj (Jul 15, 2009)

Here are some other shots of the furnace.


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## beenthere (Oct 11, 2008)

Yes. that was the blower compartment.

But. Your furnace is older then I thought. So the control for the fan speed, is in the burner compartment.

On the right hand side. The 4X4 box with the transformer and relay(known as a fan relay center) is where the blower's wires are connected for the cooling and heating speed.

Black is high, blue med, and red is low. One of them should be connected to the relays normally closed contacts so the fan limit can run the blower in heating speed. And another connected tot eh normally open contact of the relay for cooling speed. Its possible that the tech connected med(blowers blue wire) for cooling. if so, connect the black wire instead.


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## aumanpj (Jul 15, 2009)

I think this photo depicts the wire setup on the box near the transformer you are pointing me to. Is that right? How do the wires look? Can you see the adjustment needed?


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## aumanpj (Jul 15, 2009)

here are the only other 4x4 boxes that I see; although, I doubt they are where you're pointing me to. I do not see near them the transformer. Isn't the transformer the copper wire covered device?


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## beenthere (Oct 11, 2008)

The first pic with the wires, is the box I'm talking about. But the line voltage wires that need to be checked/changed. Are in the box.
Need to turn the power off and open it up.


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## aumanpj (Jul 15, 2009)

here is the back of the face plate.


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## aumanpj (Jul 15, 2009)

Here are two photos of the inside of the box. I don't see any jumpers. Hmmm... now what?


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## beenthere (Oct 11, 2008)

Follow the wires from the blower motor. What colors are connected where?

Looks loke the black(high speed) is wired nutted off.


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## aumanpj (Jul 15, 2009)

the red wire is capped off.

the blue one goes into a nut with two black wires - one of which goes into the switch on the other side of the furnace wall, the other goes into a plug labelled coil 1 at the back of the transformer.

the black one goes into a nut with another block one that enters into coil 4 at the back of the same transformer.

the white one goes directly into the switch


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## beenthere (Oct 11, 2008)

Did the blower move more or less air in heating mode last winter?

You may have traced them back wrong. The black, red and blue should not all be connected. Only 2 of them.


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## aumanpj (Jul 15, 2009)

This was our first winter in the house and so I have no basis by which to say how the heat compared.

See image for detail of wires. The only other wires in the mix are black and orange. They, however, travel to the blower door. They operate the door trip which turns the fan off when opened.


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## beenthere (Oct 11, 2008)

Ok. With the power on. Carefully turn the dial of the fan limit unit the blower comes on. Listen to it.

Then let the dial go, so the blower shuts off. Then have someone turn the fan switch on the thermostat to on. Listen to the blower. Which seemed to blower more? if by the dial. Switch the blue and black wires. If by the fan switch on the thermostat. Then the tech may have used a lower horse power motor.


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## aumanpj (Jul 15, 2009)

I put it all back together so that I could turn on the power to do as you say, and now it won't work. I get a low buzzing noise, some clicks and strange slinking noises. ugh... what have I done? I should have left this thing alone. Any idea what's going wrong?


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## aumanpj (Jul 15, 2009)

the vibration, slinking and clicking must be coming from the AC. I turned the AC circuit breaker off and now all I get is a buzzing from the furnace.

Any input from anyone would be greatly appreciated here.


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## aumanpj (Jul 15, 2009)

look at the first photo in post 10. see the red wire with a prong on the end of it... it's just loosely laying about. might it have slipped out of the back of the transformer without my knowing it and now that's what's causing my problem?


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## beenthere (Oct 11, 2008)

Yes. It is probably one of the wires that needs to be in the relay.
Should be able to look at the relay and see which slot it came out of.

The pic in post 9 is too dark for me to tell.


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## tobybul (Jul 3, 2012)

I realize this is an older thread but I have a related question. I have a Bryant HE furnace circa 1997 with a 3 ton ac. I would like to increase my fan speed also. I know that the fan is already tapped to the highest speed. Ideally, I need about a 20% increase in cfm to have better air flow in the 2 farthest rooms. My thought is to replace the fan motor with a slightly higher rpm.

I don't think it will adversely affect the discharge air temps of the unit in both heating and cooling.

Have you done anything close to this? Thanks


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## beenthere (Oct 11, 2008)

Before getting a higher RPM and higher HP motor. Remove the blower panel, hold the safety switch in, and have someone see if the air low increases to those rooms.


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## tobybul (Jul 3, 2012)

beenthere said:


> Before getting a higher RPM and higher HP motor. Remove the blower panel, hold the safety switch in, and have someone see if the air low increases to those rooms.


Not having opened the blower panel before, are you saying there is some sort of "safety switch" inside it? Does holding it down bypass fan speed controls?


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## beenthere (Oct 11, 2008)

Holding it down only bypasses it. Its just a switch that is there to help prevent someone from getting shocked/electrocuted by touching a wire in the blower compartment.


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## tobybul (Jul 3, 2012)

beenthere said:


> Holding it down only bypasses it. Its just a switch that is there to help prevent someone from getting shocked/electrocuted by touching a wire in the blower compartment.


ok, so am confused now. What am I trying to do then by holding it down?


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## Evstarr (Nov 15, 2011)

I think the goal is to see if you get more air with the door open since you'll be bypassing the filter and returns while it's open.
You have to hold the switch with your finger because the door won't be there to hold it closed.
If the switch isn't closed the blower won't work.


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## beenthere (Oct 11, 2008)

Its a way to see if you have enough return air. With the panel off and the switch held in. The blower is pulling in as much air as it can. If the air flow to those 2 rooms increases, then your short on return. And adding a return may be all you need to do. If the air flow doesn't increase, then your supply duct is too small. And putting in a higher speed, higher HP motor will make your duct system loud, and give you more air flow to all supplies, not just those 2 rooms.


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## tobybul (Jul 3, 2012)

Oh Ok. I guess I was not following that. Now that I understand I will say that the issue is not the return. In any system, there will always be an issue with return duct - and supply duct - static pressure. I agree that there maybe some cfm gained by removing the cause of return static but it won't be significant for what I am trying to attain.

When the system was installed in 97, I set up my return filtering with 2 16x25's so its a V shape. Plus I use pleated filters. This slows down the velocity of the air at the filters allowing for less static pressure and better filtering.

As to increased air flow to all registers, they can be balanced with the dampers. And yes, noise may become a factor but I don't think it will be noticeable with a 20% increase.


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## beenthere (Oct 11, 2008)

The V shape increases return static. Have you ever actually measured your static pressure?


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## tobybul (Jul 3, 2012)

beenthere said:


> The V shape increases return static. Have you ever actually measured your static pressure?


Not if the filter compartment is larger. Plus, more filter surface area reduces static pressure.


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## beenthere (Oct 11, 2008)

tobybul said:


> Not if the filter compartment is larger. Plus, more filter surface area reduces static pressure.


I take that to mean you have never measured the static.


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## tobybul (Jul 3, 2012)

beenthere said:


> I take that to mean you have never measured the static.


No I have not. But its fair to say that I have much less static thru these filter system than if it was just the standard flat filter perpendicular to the air flow. Plus, I've designed plenty of commercial systems to know.


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## beenthere (Oct 11, 2008)

V shape filter set ups are very turbulent. You should know that.

Commercial usually has a T&B done, and the pulley is sized/adjusted to get the required air flow. Seldom are they low static duct systems.


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## tobybul (Jul 3, 2012)

beenthere said:


> V shape filter set ups are very turbulent. You should know that.
> 
> Commercial usually has a T&B done, and the pulley is sized/adjusted to get the required air flow. Seldom are they low static duct systems.


I have to disagree. The velocity thru a filter with more surface area is slower than if it were flat thus reducing static or "turbulence". Of course commercial systems are designed with higher static pressures for obvious reasons. They push more cfm because they serve more square footage. Residential systems are proportionally smaller thus can be simulated accordingly.


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## beenthere (Oct 11, 2008)

There are videos showing the increased turbulence of the V shape filter set up.

If, IF, your current blower is moving 1200, and its a 1/3 HP motor spinning at 1075 RPM. Then you would need a motor RPM of 1290 to move 1440CFM(the 20% you said you want). And the new motor would need to be a 1/2HP with a service factor of 1.15. If your current motor is a 1/2 HP, then the new 1290 RPM one would need to be a 1 HP motor.


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## Doc Holliday (Mar 12, 2011)

tobybul said:


> I have to disagree. The velocity thru a filter with more surface area is slower than if it were flat thus reducing static or "turbulence". Of course commercial systems are designed with higher static pressures for obvious reasons. They push more cfm because they serve more square footage. Residential systems are proportionally smaller thus can be simulated accordingly.


Always amusing to see a newb argue with BT.  

Batter up!!! :thumbup:


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## tobybul (Jul 3, 2012)

Read your fan curves. Static pressure is not a bad thing. You just need to overcome it.


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## beenthere (Oct 11, 2008)

When you have to increase RPM and HP above normal, which increases operating cost, then the static is too much. Which is a bad thing.


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## tobybul (Jul 3, 2012)

beenthere said:


> When you have to increase RPM and HP above normal, which increases operating cost, then the static is too much. Which is a bad thing.


Am aware that there may be a need to jump from 1/2 hp to 3/4 hp motor resulting in to an increase in utility cost. But I am willing to accept that if it will improve my heating an cooling. A small price to pay for the convenience.

Better than what the mechanical contractor was proposing (take measurements $600, change to variable speed motor $1000) when in the end I know what results will be. It'll be a while before I recoup the cost. Motors are cheap and I can do it myself. This is not a commercial system with 40 hp-100 hp motors where I'm spending $10000-$20000 a year in utility cost.


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## Doc Holliday (Mar 12, 2011)

Young Skywalker < YODA


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## kilosos2 (Oct 14, 2010)

Toby

Why don't you just adjust your supply runs? Isn't that better to do and most likely cheaper? You just need some material from the supply shop... I mean why mess with your system if nothing is broken. You may end up with a bigger headache. I would change my ducts if I can access them.


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## Doc Holliday (Mar 12, 2011)

It's indefinite that his system will mess up, what BT just said. Higher static pressure will REDUCE efficiency as it extracts less heat due to air flow restriction equaling warmer and more humid supply air, eventual catastrophic floodback, dead compressor. 

Good luck OP.


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## tobybul (Jul 3, 2012)

Thanks all for your concern. I know I can make it work by increasing the cfm. Think of it this way: If this were a belt driven blower with adjustable pulleys, I would not even have this discussion. Unfortunately, its a direct drive. Finding a higher rpm motor to make it work will be my biggest challenge. The unit may be limited to just that size motor but I can't imagine that to be the case. I just need to get the specs of the existing motor so I know what to upgrade it to.

As to the ductwork, my system is properly ducted. It just needs a bit more airflow. This is not rocket science for me. Nothing catastrophic will happen. This is merely a modification on the motor. I expect that the worse that will happen is a higher supply air temp in cooling mode and a lower supply air temp in heating mode. Also, there is a slight possibility of air noise due to the increase air flow. But as long as I stay within the velocity range of the duct and the coil, it should be good. Consult your ASHRAE manuals and fan curves.

And the system will be easy to balance after.


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## Doc Holliday (Mar 12, 2011)

tobybul said:


> Thanks all for your concern. I know I can make it work by increasing the cfm....
> 
> _*As to the ductwork, my system is properly ducted. It just needs a bit more airflow.*_ _*This is not rocket science for me*_.



:thumbup:

Good luck, bud.


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## beenthere (Oct 11, 2008)

tobybul said:


> Thanks all for your concern. I know I can make it work by increasing the cfm. Think of it this way: If this were a belt driven blower with adjustable pulleys, I would not even have this discussion. Unfortunately, its a direct drive. Finding a higher rpm motor to make it work will be my biggest challenge. The unit may be limited to just that size motor but I can't imagine that to be the case. I just need to get the specs of the existing motor so I know what to upgrade it to.
> 
> As to the ductwork, my system is properly ducted. It just needs a bit more airflow. This is not rocket science for me. Nothing catastrophic will happen. This is merely a modification on the motor. I expect that the worse that will happen is a higher supply air temp in cooling mode and a lower supply air temp in heating mode. Also, there is a slight possibility of air noise due to the increase air flow. But as long as I stay within the velocity range of the duct and the coil, it should be good. Consult your ASHRAE manuals and fan curves.
> 
> And the system will be easy to balance after.


If your system was properly ducted. The those 2 rooms wouldn't need more air.

The motor you want will be a special order. And if your current motor is 1/2HP, you'll need a 1 HP, not a 3/4HP.

This is what you want


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