fan speed options

[steiny]

This isn't DIY, I'm trying to find a pro that can do this but my questions so far to locals seem to point to this not being possible unless we replace the furnance. So I figured i would ping this forum for thoughts.

We just had a central ac unit replaced and are happy with the install / pricing / workmanship. Part of the install happened to be the need to adjust the fan speed setting for the new ac unit. (old an new units are different tonnages)

The existing furnance is a trane xl 90 100k btu, it has a 4 speed blower fan.

So now the blower fan is adjusted for the heating (slot 4 high speed) and adjusted for the ac (slot 3 med high speed). All works as exspected.

But...
In our home we have the blower fan run 24/7 in order to maintain a more level temperature (2 story with basement). With the new settings on the blower fan the fan noise is much louder (as exspected since it is set higher).

Honeywell Chronotherm IV Plus is the tstat

My question:
With the above setup is it possible to have the fan step down to one of the other 2 lower speeds (like slot 1 or 2)when the fan is on but there is no call for heat or cooling? If not with the above setup would it be possible to swap out something cheaper then a furnance and get the intended result?

[BamaCool]

It can be done if your contractor is good at creating circuits.

[mchild]

If you have noise that is unacceptable then you probably have sizing problems somewhere in your duct system. The problem isn't the fan speed, it is the duct work/sizing. Your system may not be moving the air that it needs because of these issues.

Before you spend the money having someone set it up to run in a lower speed you should have the duct work fully evaluated and corrected. Undersized duct work can shorten the life of the equipment. The noise is just the symptom not the issue.

[steiny]

thanks Bamacool for the quick reply

So it sounds like I need to talk to my installer and find out if they are able to 'create a circuit' for a new fan speed. And if they are not able to I should call someone who is familar with that request.

Thanks again for the info, I'll start calling

[dash]

If you have noise that is unacceptable then you probably have sizing problems somewhere in your duct system. The problem isn't the fan speed, it is the duct work/sizing. Your system may not be moving the air that it needs because of these issues.

Before you spend the money having someone set it up to run in a lower speed you should have the duct work fully evaluated and corrected. Undersized duct work can shorten the life of the equipment. The noise is just the symptom not the issue.

stieny,

Based on times posted,I think you misssed this one.

might want to consider the advise.

Speeds between old and new unit mean very litlle,it's all based on the fan data chart of the new one,as to what speed is needed.

did you go larger or smaller with the new one?Model numbers for both would help.

[flange]

I am guessing your new unit is larger than the old one? At any rate it shouldbe pretty easy for a competant mechanic to add relay logic to make the switch occur for you. It may even be able to be done on the board without relay logic. If your guy cannot do it I would be shocked, unless of course he did this project "on the side" in which case I completely get it.

[steiny]

To the question of old vs. new blower:
The installer was able to locate a new motor with the same specifications as the previous one. Motor size / hp, the rpm's at the various speeds were not 'exact' but within a very small difference. From memory the differences were sub 5%. I don't have the part numbers on hand but I do recall the installer showing me the two fans side by side and calling out how near 'exact' they were.

To the question of how it was installed:
Definately not on the side. We went through a reputable dealer and their crew was all on the clock. Absolutely not a side job, this isn't something I wanted to save a buck on.


I believe my issue is that we (wife and I) have gotten very used to having a blower fan with which is completely silent and now that we have some noise we would like it removed if possible. While the installer was present he put the fan on the lowest setting and it worked as intended 'silent'. The issue being that the furnance doesn't appear to support that configuration.

I'll need to find a local crew that has the ability to add this feature. Much appreciated on the advice.

[beenthere]

Is it the same size furnac BTU wise as the old furnace?

[mchild]

To the question of old vs. new blower:
The installer was able to locate a new motor with the same specifications as the previous one. Motor size / hp, the rpm's at the various speeds were not 'exact' but within a very small difference. From memory the differences were sub 5%. I don't have the part numbers on hand but I do recall the installer showing me the two fans side by side and calling out how near 'exact' they were.

To the question of how it was installed:
Definately not on the side. We went through a reputable dealer and their crew was all on the clock. Absolutely not a side job, this isn't something I wanted to save a buck on.


I believe my issue is that we (wife and I) have gotten very used to having a blower fan with which is completely silent and now that we have some noise we would like it removed if possible. While the installer was present he put the fan on the lowest setting and it worked as intended 'silent'. The issue being that the furnance doesn't appear to support that configuration.

I'll need to find a local crew that has the ability to add this feature. Much appreciated on the advice.

While the blowers may have seemed very similar they may be more different than meets the eye with regard to the air being moved.

If you could provide the model number of furnace, the air flow for each speed could be checked. It may be that the heat speed on tap 4 is too high. Most units com from the factory set to high and the installer leaves it there.

The noise is most likely from the unit trying to push too much air through too small a space. With four speed taps you may be able to resolve your issue with custom engineering. Measuring your temp rise would be something to have your contractor do and will help tell you if you can drop the fan speed.

[steiny]

furnance model is TUC1008960A0


furnance hasn't changed but a new ac unit was installed, the new ac is larger and required an adjustment of the fan speeds to support the added tonnage

[mchild]

furnance model is TUC1008960A0


furnance hasn't changed but a new ac unit was installed, the new ac is larger and required an adjustment of the fan speeds to support the added tonnage

What is the a/c size?

[DanW13]

So you have a 4 speed tap settings for your furnace, one tap for heating and one for cooling, and you say you have replaced the existing OD unit with a larger one thus leaving you with undersized duct work that will not support the full amount of air needed for the new OD unit without creating noise from your registers. I think you maybe able to leave your tap speed for cooling on high and put a bypass in the duct work to allow the extra forced air to return into your return drop to reduce the excess static/back pressure. I think if you do not have the proper CFM's for the larger AC your likely to cause the ID coil to freeze up creating more prolems for you I had a 20 yr old Tempstar that was set-up as your furnace is with the tapped speeds and I recall being able to set the speeds for heating on med, cooling on med high, and fan on low in continuous run without any problems, and so I am wondering why your not able to do the same

[steiny]

a/c is 4 ton

I'm looking for exactly as DanW13 stated. Use 1 tap for heat, 1 tap for ac and 1 tap for fan.

[steiny]

oh, and currently when the fan is on continous it runs at the same speed as the ac.

[DanW13]

If you have the Tech that is currently working for you look at the wiring diagram it should show him the tapps speeds that are available, there should be one wire tap for cooling, one for heating, and one tap for fan on speed.

[steiny]

awesome!
I'll get the info to him and hopefully he can get it setup in that manner.



All the info is much appreciated.
As a homeowner that just when through the process of getting quotes / landing on a system / having the install and now working through a few glitches the entire process is rather stressful and getting 'informed' info is rather difficult. 'Informed' not implying that I've been working with people who I believe to be lacking knowledge but rather everyone seems to be very knowledgeable within their very specific brand or technology.


Being able to dig around within this forum and look for info has been invaluable towards getting me to a point where I felt comfortable spending this amount of money on a product i'll likely be using for many many years to come.

Thanks again

[mchild]

The model number does not match the XL90. Model TUC is an XB90.

The spec's for that model number has low CFM of 1,441 and high of 2,165 at .5 external static pressure. If you installer put the heat on the high speed tap then you need to get them back out to make sure it is right. They need to measure temp rise.

For the new A/C it is not right either. Depending on 350 or 400 CFM per ton it should be set differently. It is currently set for about 2,000 CFM (assuming .5 ESP). Get them back and have them also check the total ESP to make sure you are moving enough air. It is all in the Trane Product Data sheets. They need to read it.

[beenthere]

He said heat is on high, and A/C is on medium high.

[steiny]

mchild,
thanks very much for the info, when they come back out to find the fan tap i'll ask them about the cfm for the heat and cooling

[mchild]

He said heat is on high, and A/C is on medium high.

Heat on high = 2,165 when it could be on the low tap and still have reasonable temp rise of 58*. A/C on med high is 1,956 - for a 4 ton unit. Both probably would do well on the first tap (low) 1,441. Should check SC and SH on the A/C to make sure they are correct if the CFM is dropped.