Quieting the Suburban furnace model NT-16SE, same as the NT-20SE - Page 2 - Fiberglass RV


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Old 10-23-2011, 10:43 AM   #15
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David, thanks for posting this reworking of your furnace. Very nice picture of the process!
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Old 10-23-2011, 10:52 AM   #16
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Originally Posted by Frederick L. Simson View Post
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.
Well said Frederick. I do welcome posts like Byron's. If I have missed something I would appreciate a tap on the shoulder. I'm not a Kevorkian This is one reason I am doing this upgarde process publicly. It is a process of discovery for me as much as anyone, and I may at some point reach an impass that I cannot get around. Even so, the information might prove valuable to someone
David
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Old 10-23-2011, 01:56 PM   #17
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David
I think this thread is great. I don't know what furnace you are working on but Atwood makes a 12K furnace (Everest). Have you looked at the blower motor from that unit, I think it is advertised to only draw 1.8 amps. That may be an option for less power consumption.
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Old 10-23-2011, 02:56 PM   #18
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David,
Watching with interest as I have had my furnace out several times and have tried to quiet it down with everything from wrapping the case to modifying the pitch on the fan blade (which by the way are $32, ask me how I know this!!!). Wondering why you did not just remove the unit from the outside case (2 small screws and it slides right out), much easier to work on then? When you do get the mod completed be sure to use a laser thermometer to check the case temp and the front grill temp. The biggest noise maker in this furnace is the motor itself and I would stay with a dual-duty replacement motor just for safety's sake. Modifying the fan pitch did help but created another problem as it takes a pretty good airflow to initially activate the sail switch.
Here are some temps I recorded and posted on my forum after modifying the blade pitch-- http://www.casitaforum.com/invboard/...asita-furnace/

Furnace running for approx 10 minutes:

Hottest spot on top of metal cabinet 185 degrees
Hottest spot on front grille 228 degrees
Blankets/Travasak within 1" of grille 126 degrees

After shutdown:

Hottest spot on top of metal cabinet 137 degrees
Hottest spot on front grille 145 degrees
Blankets/Travasak within 1" of grille 105 degrees

Gene
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Old 10-23-2011, 06:16 PM   #19
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If nothing else is gathered than how to reinstall with better attachment points (less rattling) and support, and sound deadening, we're all good.
You've posted your preemptive warnings. Thanks for all the detail, and we wish you luck in reducing the noise.
The technology for the furnace most of us carry is not, well, not exactly space-age...
Thanks.
Sherry
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Old 10-23-2011, 06:31 PM   #20
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Thanks

Thanks LizBeth

Eddie, the blowers I'm looking at have a combined amp draw of about 1 amp, compared to 2.8 for the stock motor. Leaving out the model was a rather glaring error, sorry! I tried to go back and edit my first post to include that but couldn't. It is a NT-16SE, same as the NT-20SE

Gene, thanks for the data! Yeah changing the pitch won't work, LOL. You might even set up a vibration that makes the matter worse. You still have the power consumption issue too. You wouldn't happen to have the rated CFM of the room fan would you? I couldn't find that anywhere. I realize that the motor is a big part of the problem and that is why I'm looking at brushless ultra quiet fans. They run on double ball bearings and live a long time! One has a MTF of 50,000 hours and another 150,000 hours. That's longer than MY MTF . I'll try to follow that link and see if I get in. I'm not a Casita member. Thanks for the help!
David
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Old 10-23-2011, 06:48 PM   #21
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Cool I fixed that for you

Quote:
Originally Posted by DavidSo View Post
Leaving out the model was a rather glaring error, sorry! I tried to go back and edit my first post to include that but couldn't.
It is a NT-16SE, same as the NT-20SE
I added the model info to your Thread Title.
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Old 10-23-2011, 06:53 PM   #22
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Gene,
I can't view it without joining. Maybe I will.

Sherry,
Yeah, the housing acts as a reverberation chamber. Every noise that is produced is magnified. You could take an electric shaver that makes a nice low hum and touch the housing . Suddenly you have a very loud and annoying shaver! That part is actualy very easy to fix and I know exactly how to do it. I should have the materials for that in a few days. The mounting was disturbing frankly. I doubt that it would become an issue for most people, but I drive some aweful roads! Sooner or later that rear of the furnace would give up. The installation manual clearly states that the bottom of the unit must be supported. It is not. Aside from the mechanical strength issue, securing it will help quiet it as well. Stay tuned

Truthfully, now that I can see the issues more clearly I'm less annoyed about the unit itself. It's not as big a pile of junk as it sounds . For about $20 more Suburban could have fixed this problem though. On a $500 unit that should have been done IMO. That part IS annoying, but I know how it happens. To go in after the fact as I am and re-engineer it will probably cost me $75 to $100

David
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Old 10-23-2011, 07:13 PM   #23
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Originally Posted by Frederick L. Simson View Post
I added the model info to your Thread Title.
Thank you Frederick!

Ok, here is some additional info that I have gathered that may prove useful. I found a PDF of the service manual for these furnaces. This is what the service guys get. Even if you never service your own furnace, you should download this! In the back it has a list of estimated service times for all the common repair procedures. This might keep you from being over charged by an RV repair shop. The time they listed for the motor replacement is 1.6 hours, which sounds right on to me. These are the times that Suburban will reimburse for warrantee work, so you should not pay more either unless some circumstance warrants it. Here's the link: http://bryantrv.com/docs2/docs/ntseries.pdf

Another bit of strange info that I have gathered is this. Suburban makes two furnaces based on the NT design. They are the NT-16se, and the NT-20se. They are identical except that the 16 is 16,000 BTU and the 20 is 19,000 BTU. When I say identical, I mean they share the EXACT same parts! . Everything right down to the gas jet is the same, so how the heck is one 16K BTU, and the other 19K ?? No where is this descrepancy discussed. I'll try and dig up an answer, but one positive implication is that the unit is designed for 20-25% more heat generation than the 16 produces. It's always good to have a cushion.

David
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Old 10-24-2011, 07:23 AM   #24
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Gene,
I can't view it without joining. Maybe I will.
You won't be sorry if you do. These molded trailers are all more alike than different and there's tons of good technical stuff on the CasitaForum. Ask me how I know
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Old 10-24-2011, 08:55 AM   #25
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You wouldn't happen to have the rated CFM of the room fan would you?
David
According to the Suburban service manual that I have (available on my forum) it says the "Max CFM" for the NT-12SE & NT-16SE is 140 and the NT-20SE is 150 so it looks like the only difference between the models is the airflow?
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Old 10-24-2011, 08:47 PM   #26
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Re-Engineering

One of the big problems with attempting to re-engineer something like this is not knowing all that was taken into consideration during the design process and all the information gathered since the initial release. Generally speaking when something is released for consumer use there's been lots and lots of hours spent in making the design work within the design requirements. It's just one person either, it's several. Have no real idea why the air flow is set where it is, but I'm sure there's a very good reason for it. The over heating was a speculation on my part knowing a bit about air flow, heat management, and other interesting engineering things.
Here's where a bit of research could come in handy. I suggest that an attempt to contact any furnace manufacturer's engineering department. See if you can find an amiable engineer that might shed some light on why the air flow is set where it is. There is a reason.

It's usually quite difficult to have a successful re-engineering of a product that's been around for as long as these little furnaces have been around.

Good luck and be safe.
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Old 10-25-2011, 11:41 AM   #27
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Originally Posted by Byron Kinnaman View Post
One of the big problems with attempting to re-engineer something like this is not knowing all that was taken into consideration during the design process and all the information gathered since the initial release. Generally speaking when something is released for consumer use there's been lots and lots of hours spent in making the design work within the design requirements. It's just one person either, it's several. Have no real idea why the air flow is set where it is, but I'm sure there's a very good reason for it. The over heating was a speculation on my part knowing a bit about air flow, heat management, and other interesting engineering things.
Here's where a bit of research could come in handy. I suggest that an attempt to contact any furnace manufacturer's engineering department. See if you can find an amiable engineer that might shed some light on why the air flow is set where it is. There is a reason.

It's usually quite difficult to have a successful re-engineering of a product that's been around for as long as these little furnaces have been around.

Good luck and be safe.
Byron,
It is entirely possible that the solution will be a fan that produces the same amount of air, but at a lower noise level. Steeply pitched metal blades like the one used in the furnace are cheap but noisey. Motors with brushes are noisey. There are fans that turn significantly higher RPM with shallow pitch, produce the same CFM, and are quiet. My comment about air flow was that the scamp does not need 140 CFM to move the air around that small space. If lower air flow results in an overheat, that will be revealed in the testing.

It's also possible that my work could result in a SAFER operation. Here's one example that I'm looking at. To get 140CFM out you have to have 140CFM in. Where is that air coming from? There is no dedicated air vent to supply the heater with room air. The air comes from passages left around cabinets, around the doors, stovetop, and other places. Nobody would block a dedicated air vent, but various modifications or cargo could easily block passages that normally supply this air. If for some reason, the passages were blocked enough that the fan produced a vacuum in the cabinet, it could possibly suck CO out of the exhaust connection. Most people probably don't know, but the exhaust connection is not a solid connection. It is a loose slip joint that depends on the scavenging effects of the passing exhaust and a neutral cabinet pressure to take the gas out. I really don't like that. Such an air restriction could also result in overheating. The unit can be rated for whatever you want, but the airflow will not be greater than what is available to move. Restrictions increase noise too. Put your hand over the hose on your shap vac and listen to the motor.

The final operation and safety of these units is the product of the original design and the installation.

What I'm saying is that my work is getting a lot of attention because it is on the furnace itself, but people could be endangering themselves more with something as seemingly innocent as a cabinet modification. I'm trying to de-mystify some of this for the general good. Any modification to a trailer, whether simple or major could effect things that impact safety in unforseen ways.

I should also restate that what I'm doing is 100% for my own use. I'm sharing the process for the sole purpose of information exchange. It's not an attempt to convince anyone of anything. People can (and should)judge the competency of what I do for themselves and act accordingly. I could post my credentials, but what use is that on the internet? It would be no more believable than anything else I'm doing.

David
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Old 10-25-2011, 01:07 PM   #28
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Originally Posted by DavidSo View Post
<<< snip >>> The modifications will include sound deadening of the sheet metal housing, <<< snip >>>David
David...

Damping the vibrations of the sheet metal housing is going to give more bank for your buck that you would ever imagine. I have applied high-temperature "sound deadning" sheet to selected portions of the housing with remarkable results. My intentions are to pull the guts out of the furnace housing and judiciously apply additional vibration damping materials... so much of the furnace and its housing truly ring like a gong! Every bit of vibration from the fan(s) is efficiently transfered into the sheet metal, exciting resonances and vibrations all over the place... dang!

I don't know if you have sniffed around the other [Casita] Forums about this topic... several of us have been fiddling with (albeit pretty sporatically) trying to quieten the furnace for the past year and a half or so.

An "ideal" solution for me (and one that would not modify the basic engineering of the furnace) would be (1) proper vibration damping of thesheet metal, and (2) a "soft start" electronic circuit that would ramp up the fan over aone or two-second period (from OFF to FULL ON)... it's that jarring rrrrrrrooooooooaaaaaarrrrrrrrr when the fan turns on that drives me bonkers.

Cheers!

Rob
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