Quieting the Suburban furnace model NT-16SE, same as the NT-20SE - Fiberglass RV


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Old 10-22-2011, 08:55 PM   #1
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Name: David
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Quieting the Suburban furnace model NT-16SE, same as the NT-20SE

Well I got started on this today so I'll begin with some introductory info. My goal with reworking this furnace is 3 fold. I want to quiet the furnace so that I can sleep without interruption, increase the electrical efficiency so it doesn't produce such a hit on the battery, and lastly eliminate the liability of a costly fan moter replacement.

In the process of disassembly I realized that the procedure would be helpful to anyone who may have to simply replace their existing blower motor. Some might want to bookmark that procedure.

I've got lots of pictures and I'll try to explain the work in detail as I go. I have taken the furnace apart to assess the possibility of the upgrades. So far it looks very promising! I did not want to alter the saftey interlocks, or the operating logic and it appears that can be easily avoided. The existing blower assembly does not have high temp requirements, so that relieves another possible concern. The existing fans and motor take up a lot of space in the housing so there is plenty of room for retrofit parts.

So here we go. I have pics to process and then I'll start posting what I have thus far. Questions welcome

David
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Old 10-22-2011, 09:22 PM   #2
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I have heard of people trying to install sound baffles around the furnace to reduce noise, but your project is the first I can recall of its kind... actually changing inner components. Do you have a decibel meter to measure the before and after sound levels? It will be interesting to see what you can do! Those furnaces sure are loud.
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Old 10-22-2011, 09:28 PM   #3
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Quote:
Originally Posted by Mike Magee View Post
I have heard of people trying to install sound baffles around the furnace to reduce noise, but your project is the first I can recall of its kind... actually changing inner components. Do you have a decibel meter to measure the before and after sound levels? It will be interesting to see what you can do! Those furnaces sure are loud.
Mike,
I used to have some really high end sound measuring equipment, but that was before I lived in an egg . Most people don't understand Db measurements anyway. It is measured on a log scale, and unless you are an engineer or mathmetician the numbers are greek. For now, subjective impressions will have to do. For me the best measurement is whether it wakes me up
David
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Old 10-22-2011, 10:00 PM   #4
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Name: David
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Furnace Removal

Removing the furnace is fairly simple. here are the tools you will need to remove the unit and replace or remove the blower motor:
3mm allen wrench
3/8 socket on an extension
magnetic screwdriver (phillips #2)
channelock pliers
2 8" adjustable wrenches
wire cutter
most pictured below
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Yeah, well, I cut myself twice getting it out so be careful Before you start make sure the thermostat is fully off, or the battery cable pulled. Also shut off the gas at the tanks.

The grill comes off with two screws. After that you see this:
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Inside the small box in the lower right corner is the gas connection.
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Two adjustable wrenches will break the connection. be sure to support the furnace side of the connection with one wrench while turning the line side. Once the connection is separated, you can push the line out the hole into the cabinet. On mine somebody had taped the wires to the gas line. I had to pull them both out the front to separate them.
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The wires on mine were wire nutted together. I just removed the nuts and taped the ends. When I reinstal the unit, I will install a proper plug.

Note, there is a screw that protrudes out of the housing on the right side where you would reach in to pull out the wires. Watch for it or you will get cut. On my furnace the gas line was a pain to get out of the way because there was no room to push it out the hole. It hit the closet wall. I suspect it was installed before the closet was there. When I reinstall I will use a 90 degree connection and end that nonsense. <_<
David
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Old 10-22-2011, 10:15 PM   #5
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Furnace Removal 2

There are 2 screws holding the unit in the cabinet. They located here:
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I removed them already but they were on each side of the yellow sticker. Once the gas, wires, and 2 screws are out, you can pull the unit out of the cabinet. There are no connections in the back The intake / exhaust tubes will separate.
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Note: IMO this furnace was not properly supported. It is supported in the back entirely by hanging on the tubes. In the front it rests on the edge of the fiberglass with a little strip of aluminum. All this loose attachment is part of the reason it makes so much noise. I'll be building proper supports under it when I reinstall.
David
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Old 10-22-2011, 11:06 PM   #6
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Furnace Disassembly

Once you have the furnace out you will see that all the components are installed through the ends of the housing. There is no way to open it up. The blowers are located at the rear of the unit and can be easily removed from there. Stand the furnace on end with the back up and you will see this:
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The tube on the right is the combustion chamber exhaust. On the left is the inlet. The black housing is the intake air plenum for the combustion chamber. There are screws all the way around that must be removed. use a magnetic screwdriver to keep from dropping them. They are all the same but one! The screw that goes through the metal support bracket below iis different, so keep it separate. In the photo I have already removed most of them.

I flattened the flange around the edge of the housing with channel lock pliers where the screwdriver needs to access the screws that separate the air plenum.
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Once all the screws are out, pull the top of the plenum off and you will see this:
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This squirrel fan is attached to the back of the blower motor and provides the combustion chamber air. One motor powers both the combustion air and the room air. This fan is removed by loosening the locknut on the collar with a 3mm allen wrench. I was a bit confused by this because a standard wrench is too long to fit inside the fan. I tried to go through the side with the long end of the wrench but the blades are too close . I ended up cutting my wrench down with a cutoff tool. With the nut loosened a bit you can slide the fan out. After I got it out I realized that the fan has a hole in it to access the nut! You can reach it through the louvers in the housing.
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Old 10-22-2011, 11:35 PM   #7
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Furnace Disassembly 3

Ok, with the fan out you have this:
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Remove the two nuts holding the fan motor with a 3/8's socket and extension. Support the motor and let it lower into the housing. There are 4 additional screws to remove that hold the plenum half to the lower support brackets. The 2 pairs are different so make a note of where they came from. The 2 bigger ones hold the plenum to the combustion chamber inlet. Pull the plenum half out and you have this;
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The motor will be sitting there with wires attached. You have two choices now. You can cut the wires and use connectors to reattach the new motor, or you can follow the wires to where they plug in and pull them. I would advise against that! They are damn hard to get to and you could end up damaging something in the process. Replacing them will be harder than pulling them! If you want to do that though, the red wire connects to a circuit board accessable through the back of the housing with a long needle nose plier. The black wire must be pulled through the front of the housing using the long pliers, and is attached to a ground buss bar. I cut mine

Now you have the moter out, and if you plan to replace it you just reverse the steps. We aren't doing that, as I will be replacing that motor entirely.
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You can see the front room air fan here still attached to the motor. Notice that extreme pitch? That fan is designed to move air through the front of the furnace and also supply an optional side duct. That is why the damn thing makes so much noise. We don't need that much air movement in these little trailers. I can get a nice gentle breeze out the front with an efficient and quiet brushless DC fan. Zero vibration.
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Old 10-22-2011, 11:50 PM   #8
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The plan

Well now I have to do some research to find the right fans to fit the spaces I have here. Luckily there is plenty of space for the room air fan. The combustion fan may be a little harder to source. Instead of one motor driving two fans I'll have separate motors/fans. This will work fine except for one thing. The sail switch which shuts down the furnace if the motor dies is blown by the room air fan. In the original configuration it's the same motor for the combustion so it doesn't matter. With two fans, the room air fan could continue to blow the sail switch while the combustion fan has failed. I think I know a way around this .

It may be a while before I continue this project. I'll need to order parts. My intention is to do this as simply as I can so others can copy it if they like. Hopefully what I've described so far makes sense, I'm pretty tired
David
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Old 10-23-2011, 06:55 AM   #9
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very interesting....
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Old 10-23-2011, 07:58 AM   #10
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Dangerous

This looks like a pretty risky undertaking and possibly very dangerous. If you reduce the air flow across the fire box it's going to get hotter, possibly hotter than designed to work without damage. Also there's a pretty good chance that with less drag on the motor it will run faster causing more air to the burner, thus a hotter flame.

I would be more concerned about sleeping forever than waking up a bit when the blower turns on. I found I got used to it pretty fast. I usually hear it come on which is reassuring that it's working, but it doesn't wake me up enough that I miss much sleep. Along with that morning has no specific time to get up when Scamp living.
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Old 10-23-2011, 09:34 AM   #11
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David,

Great description of the disassembly of the furnace. I'm sure it will help someone in the future who simply wants to remove or repair their furnace.

Obviously there will be some trepidation over your redesign. Personally I support your effort and feel you are aware enough to do appropriate testing. Certainly there is risk associated with your project, but from my perspective all adavnces in design carry a measure of risk.

Wishing you well and hope you are as careful in your design as you were in your description of the removal. Looking forward to your results.
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Old 10-23-2011, 10:12 AM   #12
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thanks

Thanks Norm,
If you feel the thread is inapproriate you have my blessings to delete it . I'm not encouraging anyone to do this if they feel uncomfortable. These systems are actually quite simple, but I understand the reluctance.

I think retaining the motor replacement info is useful though at the very least. It is very straight forward, requires simple tools, and would save someone a ton of money.

I do have air speed measurement equipment, an infrared thermometer and other diagnostic tools. I'm not doing this blind. The modifications will include sound deadening of the sheet metal housing, improved mounting of the unit, and the internal modifications to the blower section only. People can stop wherever they feel comfortable.

With regard to the overheat question, the system appears to have internal heat protection. There is a limit switch which I think is thermally activated. It's easy enough to check with a heat gun. If it overheats it will simply shut off. The flame can also be visually inspected through an observation port for proper function. I don't plan to cut the airflow anywhere near that far.

Still, I'd be happy to drop the subject with no hard feelings if you guys see fit

David
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Old 10-23-2011, 10:31 AM   #13
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Keep it going.
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Old 10-23-2011, 10:35 AM   #14
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Quote:
Originally Posted by DavidSo View Post
If you feel the thread is inappropriate you have my blessings to delete it . I'm not encouraging anyone to do this if they feel uncomfortable.
You cannot please all of the people all of the time. That should not prevent you from sharing your endeavors. As Norm said, this is an excellent tutorial on just the disassembly of the furnace. Knowledge is a tool to prevent being taken advantage of by service providers for those who choose to hire their work done by others.

Members must accept that everything presented here is at the individuals' own risk. Knowledge of that risk is also valuable! Byron adds a dimension to that knowledge and I applaud his desire to keep us all fully informed.
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