Quieting the Suburban furnace model NT-16SE, same as the NT-20SE - Page 3 - Fiberglass RV


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Old 10-25-2011, 05:32 PM   #29
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Name: David
Trailer: 16 foot Scamp
Oregon
Posts: 314
Rob,
Yeah, I wish I still had my sound measurement equipment to quantify the effect that each step has. If you have read through my posts, the metal housing is high on my hit list. I do not believe that additional sound deadening mat on the inside will gain you anything though. It would if the problem were noise transmission through the housing. The problem though, as you stated is resonance. Once the resonance is killed, that magnification of the vibration is done. I'm pretty sure the outer coating accomplishes that. To prevent the noise from the fan from exciting the housing it would have to be enclosed (impossible). The sound shield would have to include a suspended septum. This type of sound containment would be more useful on the inside of the cabinet than the inside of the housing.

My mat just arrived today and it is a new product to me called Boom Mat. It is high temp compatable and metal backed. I'll let you know if it's any good once I get it on.

I agree that the start up is jarring. That's what wakes me up. You are out in the woods in total silence and then CLANNNGGGGGROAAAARRRRRR!

At present I'm only a member here, so no I haven't looked around much. Donna and Gene are working my elbow joint pretty hard though

David
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Old 10-25-2011, 09:01 PM   #30
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Name: George
Trailer: Waiting for the Sprinter van and designing the converion modules.
Oregon
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Did you consider separating the two functions from the motor to one motor driving combustion air and another one for recirculating air in the trailer. You could then place the recirculating air unit in a place allowing for easy reduction of transmission motor vibration into a cabin and use input and output mufflers to muffle the fun noise. It would require a lot ducting work, but, good sleep is like gold just don’t engineer it to be a permanent one. See Truma side (in American English it should be spelled Wallet Trauma), somewhere there I have seen mufflers in their installations. I like their idea of combining a water heater with a space heater, unfortunately it is 220V and it is not approved on US roads. I while back my 1985 Westphalia VW had Eberspacher heater (gasoline powered) installed in Germany during my European delivery. This was a very quiet heater as well, but I don’t think they have a LPG model. Eberspächer UK
Truma - Gas-electric heating systems
Good luck,
George.
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Old 10-25-2011, 11:28 PM   #31
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Name: David
Trailer: 16 foot Scamp
Oregon
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George,
Here's a quote from my post #8:
" 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."

2 fans was always the plan.

I understand your point about remoting the room air fan but that is not practical with the existing unit. The housing is the air duct and it is mounted very close to the wall of the trailer. I do plan to mount the room air motor on rubber isolators.

David
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Old 10-25-2011, 11:52 PM   #32
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Name: George
Trailer: Waiting for the Sprinter van and designing the converion modules.
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Originally Posted by DavidSo View Post
George,
Here's a quote from my post #8:
" 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."

2 fans was always the plan.

I understand your point about remoting the room air fan but that is not practical with the existing unit. The housing is the air duct and it is mounted very close to the wall of the trailer. I do plan to mount the room air motor on rubber isolators.

David
I missed that,

Good luck,

George.
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Old 10-26-2011, 12:05 AM   #33
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Trailer: 2009 Trillium 1300 "Homelet"/2014 Subaru Outback "Rosie"
Washington
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Reading this thread I have a couple of thoughts:
1-Could the fan be replaced with one designed for electronics or computers?
2-Maybe the only difference between the two BTU rated models is a slightly bigger gas nozzle orifice on the higher rated one, something that wouldn't be obvious. A few thousandths larger diameter would increase gas flow enough. 16 to 20 is only a 25% increase. A 25% increase in area would be achieved by an orifice just 10% bigger in diameter. Changing anything else in the design would not be economically feasible. Probably designed for the 20 and reduced the orifice for the 16. Hmm. I wonder if they offer an even smaller orifice to reduce the BTUs to 12 or even 10? Maybe the burner fan changes a little for the different ratings, or a flow restricter for the burner air?

BTW: Lots of good information at: http://www.propane101.com/index.htm

Read especially: About Propane, Propane Tanks, and Regulators
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Old 10-26-2011, 10:41 AM   #34
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Name: David
Trailer: 16 foot Scamp
Oregon
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George,
No worries! your ducted air idea has merit too. It could be done through the side but I'd sure like to avoid it if possible. It would be nice to have it all inside. An air duct to supply air from outside the cabiinet is also a possibility. I appreciate all the thoughts because i don't know where this project will go once I get into it. It could be that the ideal fan can't live in the housing because of heat. I hope that is not the case.

Roger,
I've thinking along some similar paths. The brushless 12V DC fans that I'm looking at are used for all sorts of cooling, including electronics. the smaller more common versions are the "muffin fans" that most of us are familiar with. I've used these fans for a number of projects over the years with good results. I have never had to replace one either. They seem to run forever and they consume little power.

As for the BTU, my suspicion is as you stated. Even though they list the jets as having the same part number, I'll bet they are different. They do make an NT-12se as well! That means that we could just swap jets and get a lower heat output. I have felt from day one that the heater in my trailer is too big. I think it would be better if it ran longer per cycle at a lower output. That would warm the trailer more before it shut off. As it is, the temp rises so quickly that the thermostat kicks off because of the spike in air temp. I would like to experiment with jet sizes. If we can get a 12K BTU jet we can always ream it if need be to customize the output. I'm guessing that 12k would work well.
David
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Old 10-26-2011, 11:46 AM   #35
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Name: Robert
Trailer: Airstream 23D International Serenity
Texas
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<<< snip >>> 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.
Actually, there is just such a 'dedicated' return air grille in our 2010 Casita Spirit Deluxe.


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<<< snip >>> 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. <<< snip >>>
Not only is there a grille, the backside of the furnace is in space common to the sink/stove cabinet and to the space beneath the [street side] rear bench. A year or so ago, I did a practical 'test' to see what would happen in I were to completely block the return air grille... nothing... the fan still blew like crazy with no apparent change in the 'sound' of the fan. Apparently, the whole 'under counter' area is so 'leaky' adequate air can easily be supplied even if the grille is 100% blocked. Of course, this was a sample size of one, which, in the grand scheme of things means nada!
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Old 10-26-2011, 11:56 AM   #36
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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 .

<<< snip >>>

David... I'm eager to see how you are going to work around this show-stopper of a problem. Failure here could ruin your entire weekend (well, at least it would probably be a short weekend ).

Rob
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Old 10-26-2011, 12:05 PM   #37
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Trailer: Waiting for the Sprinter van and designing the converion modules.
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Inline blower

If you decide to go with an inline blower Attwood makes a couple of units. Not knowing how this blower would function in the hot air I would place it upstream. Marine Blowers, Boat Blowers, Boating Lift Blower : Attwood Marine
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Old 10-29-2011, 07:09 PM   #38
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Trailer: 2002 Casita 17 ft Spirit Deluxe
Arizona
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I have the same furnace in a Casita SD 17'. I had to go back and see that yours is in a Scamp. Casita has the output end resting on a piece of 2"x2" wood fastened with 2 screws. The other end rests on top of the wheel arch, but has no fasteners. I positioned it carefully when I installed it before boring the holes for the stacks.

Mine is out and apart at this time because the room air impeller came loose, slid off the shaft and was bent up. I do recommend using Locktite on the fan set screws.

I found that the guts will come out of the outer housing without difficulty. They are held by a metal screw adjacent to the propane fitting. Greatly enhances the accessibility.
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Old 10-29-2011, 08:50 PM   #39
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Name: Doc
Trailer: TrailsWest CAMPSTER 1970
Washington
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David, I am watching your educational furnace upgrade with high interest. Mainly because I hate noisy electric fan furnaces along with my dislike of the catalytic type.

I am glad that you are making sure the 'Over Heat' switch is operating so you will have a 'Fail Safe' aka Fire Safe unit.

Your photos are really well done and appreciated.

I really wish the old 'Gravity' type Hydro Flame & Coleman furnaces were still available. They were quiet and did NOT drain the battery.

Thank you Dave,
Doc the boonDOCer.....of campfrugal
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Old 10-30-2011, 08:50 PM   #40
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Name: David
Trailer: 16 foot Scamp
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Thanks for all the replies and ideas! I'm still researching fans, and I got sidetracked by my real job . I'm pretty sure I can just add another sail switch in the blower plenum and wire the two in series. Some adjustment of the sail may be needed to match the lower output of the combustion fan. That way a failure of either fan will shut the unit down. I consider defeating any of the safety features as a failure of the project. It's not an option.
David
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Old 10-31-2011, 03:24 PM   #41
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Name: David
Trailer: 16 foot Scamp
Oregon
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room air fan found

Well, I have found a candidate for the room air fan. It is 7.5 inches diameter, produces 166cfm (24cfm over stock), draws just .7 amps, 1300 rpm, rated life expectancy 40,000 hours. Operating temp up to 200 degrees. Just 37 Db-A

I don't want the thread full of conflicting info so I'm withholding the model info till I confirm compatibility. The fan has speed modulation capability. Not sure I'll use that. There is a Youtube video of the fan, recording the noise level. Very Quiet! I'll share all this later so I don't run people down blind alleys!

The crazy thing is this. You buy an "RV" fan motor that draws a ton of power, has a limited life, and is noisey, for well over $100. You buy a computer type fan like this for $12 + shipping. I bought 3 and got free shipping! The market is so huge that the end pricing is low. I figure I'll use them for cooling fans around the coach since they draw so little and move so much air. I'll also have ready replacements for the furnace fan if one does fail.

My only real concern is whether the heat is high enough at shut down to affect the fan. During operation the fan is self cooling since it is a pusher. At shutdown it will have to sit next to the cooling combustion chambers. The fan is very thin so it can be moved to the rear of the case away from the burner section. There is about 4-5 inches of separation. The factory fan is so long that it runs about an inch from the combustion chambers. A short shutdown delay of maybe 1 minute would remedy the problem if it comes up.

Finding this fan is a major step forward if it works out.
David
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Old 11-04-2011, 12:10 PM   #42
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Trailer: 1977 Scamp 13 ft
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I picked up a New all-be-it older 1200SE Model and I believe that it is slightly quieter than the 1600 + units.

One thing I noticed was one time my battery was just about depleted and I had exactly 12V on it, the furnace seamed to run fine but significantly quieter. That gave me an idea to try something. I had a universal laptop power supply for a car 12V plug that supplies up to about ~4 amps at 12V and i ran that in between the battery and the furnace, the difference in sound its very noticeable. I figure that the furnace is designed with the possibility of running on a discharged battery system, and 12V is not quite a dead battery. If your plugged into shore power your line voltage at night to your furnace is probably going to be closer to 14V or so. Anyway ran it that way for a couple of trips without any issues. I needed my power charger so I pulled it back out since then. I figure that the manufacture designed it so that as long as you are pulling the sail switch open you're in the clear for undervolt. Allthouh it could reduce the life of the motor the electronics themselves are most likely ran on much lower voltages with MOSFETs to regulate the voltages. Ill leave that to you engineering people to debate.
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