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Old 11-19-2014, 08:04 AM   #1
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Furnace Replacement

I am replacing the furnace in my 1979 28' AS. The previous owner removed the old furnace. Does anyone know where the return air for the furnace comes from. Mine appears that it is closed up in the cabinet. In addition to the fresh air intake and exhaust vent there is a third single two inch whole about 1 foot above the exhaust through the outer skin. Not sure what this was used for but there are a few 2" holes in the cabinet walls for routing a flex hose that don't look factory. I am attempting to install the new Suburban NT30SP furnace. Any assistance is greatly appreciated.
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Old 11-19-2014, 08:26 AM   #2
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I am replacing the furnace in my 1979 28' AS. The previous owner removed the old furnace. Does anyone know where the return air for the furnace comes from. Mine appears that it is closed up in the cabinet. In addition to the fresh air intake and exhaust vent there is a third single two inch whole about 1 foot above the exhaust through the outer skin. Not sure what this was used for but there are a few 2" holes in the cabinet walls for routing a flex hose that don't look factory. I am attempting to install the new Suburban NT30SP furnace. Any assistance is greatly appreciated.
Sounds like a after market modification.

How about a couple of photo's?

Andy
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Old 11-19-2014, 09:30 AM   #3
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Thanks. I will get a few photos. Any idea where I can find the 4x6 register for and duct adaptor for this application. The old part numbers from my service manual are 600669 (register), 600975 (adaptor), and 600974 (furnace adaptor).
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Old 11-19-2014, 10:09 AM   #4
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Attached is the photo. Any idea what the top hole was used for?
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Old 11-19-2014, 02:06 PM   #5
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Attached is the photo. Any idea what the top hole was used for?
What's the orientation of your photo?

Are those holes side by side, or one over the other?

Andy
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Old 11-19-2014, 03:03 PM   #6
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Thanks. I will get a few photos. Any idea where I can find the 4x6 register for and duct adaptor for this application. The old part numbers from my service manual are 600669 (register), 600975 (adaptor), and 600974 (furnace adaptor).
600669 has been replaced, but is still available.

The other 2 numbers are obsolete.

Andy
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Old 11-19-2014, 07:32 PM   #7
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The photo should be rotated clockwise 90 degrees. Sorry, not sure how to do that. The two holes together which would be the bottom of the image are the furnace fresh air intake and exhaust ports. I can't figure out what the top single hole was for. There is some after market holed drilled in the cabinet for what appeared to accommodate a 2" hose behind the single hole in the outer skin.

Andy, what is the new part number for the furnace register and where can it be purchased. Maybe it is designed to fit the new Suburban NT 30SP furnace and does not require the adaptors any longer?
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Old 11-19-2014, 07:35 PM   #8
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My Suburban NT30, not an SP model, had the cold air return as a grate, or grill in the cabinet door in front of the furnace. The installation instructions specify the size of the opening in front of the installed furnace for cold air return. Maybe the SP is similar.

There is an outfit called D&W Incorporated in Elkhart, IN, that has been making RV ductwork for years. They may be able to help you with a 4x6 register and adaptor. They have an on line catalog and ordering system. Easy.

I'm sorry, I do not recognize the 2" hole in the side of your trailer. I've installed three furnaces in my two trailers, but never had a hole or accessory like that. It almost looks like the hole in my 66 Trade Wind for the whip radio antenna. I'll bet someone else will know what it is for.

David
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Old 11-25-2014, 06:35 PM   #9
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Matching The Furnace Ducts

I did not remove the old furnace so I am figuring out the install as I go. Received the new NT30SP today. It fits in palace and the exhaust and fresh air intake match up. The two 4" ducts on the furnace do no align with the metal duct that was left in the trailer or the two" duct that runs below the sub flooring. There is only a few inches of space between the side of the furnace and they are vertically mis aligned with the trailer metal duct that run the length of the trailer to the rear. I don't think there is enough room for a flex duct to join the furnace to the duct. Does anyone know how this ducting is joined together. Thanks
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Old 11-25-2014, 09:07 PM   #10
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Hi Highway Man. You are on your way to installing your new furnace. I wonder if you can take a picture of your existing ducts and how you have to match up to your new furnace?

I am dumb on furnace duct fittings. I don't know a boot from a 10x4 to oval connector. They are worse than plumbing fittings and hydraulic fittings. A whole new langauge to learn.

But, most Airstreams use 4" flex ducting. And you can buy connectors from flex to 4" round sheet metal tube ducting, and you can buy 4" round to 10x4 square registers, and 4" to 2" reducers, etc, etc. R&W in Elkhart, IN, supplies the RV industry with all sorts of HVAC fittings. Their catalog is on the internet. They might have what you need. I orders several parts from them. And I also bought fittings from Menards.

You might have to innovate some new ductwork here and there. Your instructions for the NT30 likely say to use at least three 4" round openings to get the hot air out. And likely a 12" square opening to get cold air back to the furnace. My trailer has a decorative screen built into the cabinet door in front of the furnace for this purpose. It's important.

I included a photo of my furnace in the 66. But I went with bottom ducting under the floor. You can see the 4" round connectors for the ducts above the floor which is a much more common method. I used the blanks to close these offs on my install.

Keep us posted as your project progresses. Be sure to check for propane leaks.

David
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Old 11-25-2014, 09:21 PM   #11
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From looking at the other threads regarding furnace installation it is definitely going to take some duct fabrication and re-routing. I am going to reach out to R&W for parts. The furnace is too high. I may have to cut out more subfloor and go with the bottom duct. I will send a photo tomorrow. Thanks for the photo David . That is a nice clean install.
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Old 11-26-2014, 05:42 AM   #12
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Good Morning Highway Man. I went with under floor ducting because I had the belly pan down for my frame inspection, bath subfloor replacement, insulation replacement, and waste water tank installation. The old 66 Trade Wind had a furnace that blew warm air into the trailer, and drew back cold air from floor registers and under floor ducting. It did not have any warm air ducting routed to the bathroom, and this would have been difficult due to the twin beds and under bed storage bins in my trailer. There is big honk'in wheel house covers under the beds!

So.... I elected to try under floor ducting. I have not used the system in cold weather yet. I do get decent air movement out of the two floor registers. One of my duct runs goes to the waste water tanks. Cold air return is from the front of the furnace. My floor registers do not have dampers on them as you can't choke off the furnace warm air delivery. I got my flex ducting, connectors and registers from R&W

My 86 has above floor ducting except for the run to the waste water tank compartment and the run under the floor to the side bath. The 86 actually has two furnaces.

Here is a photo of my below floor plenum with a 4" flex ducts connected to it. One goes to the front register, one to the tank compartment, and one to the rear bath floor register. I subsequently insulated the floor and around the ducts to hold some heat in.

We'll look at your photo and offer a bunch of FREE advice! Can't beat that!

David
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