Furnace Replacement

[Bethany533]

I have a Suburban NT-30 S furnace that needs to be replaced. I've read through many of the old posts to get some background info. From what I understand the Suburban NT30SP or NT34SP would be the correct replacement. I recenlty acquired my 1984 300. I've never used the furnace so not sure if would be best to upgrade to the 34,000 BTU or just stick with the 30,000 BTU. Any thoughts?

[Aage]

Interesting thing about the three Suburban furnaces: from the spec sheet, the only difference apart from the BTU input (heating power) is the current draw of the fan motor. They all weigh the same, have the same dimensions, look the same.

So, there's the 30k and the 34k models. My '74 Sov has a 32k, so I felt that there couldn't be a huge difference in what a 30k OR a 34k could do heat-wise. I live in a colder climate, but I don't live through the winter in it. Spring and fall, I just wanted to extend the time I could spend in the trailer.

So, the current draw on the 30k model is 4.5 amps, and the 34k is 7 amps. I wanted the quietest one I could have, so I took the 30k.

I hope I chose right!

[Mike Leary]

The lag with Suburbans and our need for heat is to order too large of a unit which does not provide proper cooling of the housing. In other words, if the furnace has four knockouts for distribution, you better use them. If you use only two or three, get set for big fun with the high limit switch and everything else. Oh, by the way, I know the hard way and the tech that installed it has heard nothing but guff from me.

[litlgeezer]

I'm sorry, but I thought this might be an appropriate jumping on place. I am a new member who recently acquired a 1972 Int'l Sovereign. I probably paid too much for it ($6,500) as I have found a few items that need repair or replacement. I removed the Suburban NT-30 S furnace after finding that the burner tube was rusted out. A factory Airstream tech emailed that a NT30SP was the correct up-grade for it. Because of the very tight space next to the original water pump, I decided not to remove the furnace housing. Instead, I want to purchase another furnace and insert the new 'guts' into the existing housing. Can anyone tell me for sure that the 'guts' of the new NT30SP will slide into the existing housing AND match up to the exterior inlet/exhaust holes? Thanks for any helpful responses you can offer.

[idroba]

Originally Posted by litlgeezer

I'm sorry, but I thought this might be an appropriate jumping on place. I am a new member who recently acquired a 1972 Int'l Sovereign. I probably paid too much for it ($6,500) as I have found a few items that need repair or replacement. I removed the Suburban NT-30 S furnace after finding that the burner tube was rusted out. A factory Airstream tech emailed that a NT30SP was the correct up-grade for it. Because of the very tight space next to the original water pump, I decided not to remove the furnace housing. Instead, I want to purchase another furnace and insert the new 'guts' into the existing housing. Can anyone tell me for sure that the 'guts' of the new NT30SP will slide into the existing housing AND match up to the exterior inlet/exhaust holes? Thanks for any helpful responses you can offer.

Probably not. Although the box size may be the same, the new ones have a different electrical connection system, different cooling vent holes for the electronic ignition, and usually a different gas inlet location from the one you have in a '72. The outside inlet and exhaust tubes probably are in the correct location.

I would recommend you consider changing both the guts and the box both. It is not difficult to remove the box, it is generally held in with only two screws in the bottom, near the front. It will slip right out, assuming that you are not one of the unlucky ones with a furnace with a shelf on top of it, and a bar in front of it.

Let us know how you make out.

[edglenn]

I just went through these same issues with my new Suburban furnace I put in my '69 Overlander, so here's my 2 cents:
First: The original Suburban furnace and the new replacement units are NOT one-for-one. You won't be able to re-use the old housing, the furnace duct doesn't line up, and the inlet/exhaust is at a different elevation. You'll have to frame up a pedestal to mount the new unit, and fabricate some duct. No big deal, you can do it. It will take at least a day or two, if you're handy with tools. Be prepared for a real hassle connecting the propane fitting. It's right at the bottom corner (?!?).
Second: the actual furnace (enclosure, fan, heat exchanger, etc) is pretty good quality, but the electronics are NOT. Plan on replacing the original control board with a new "Dinosaur" board pretty quickly. The OEM board material and components are cheap, which is surprising, because the board is manufactured by Fenwall. (Fenwall used be be outstanding in the controls industry.) I had nothing but problems with the old board, which was traced back to a $0.50 connector and a bowed circuit board. So I spent another $150.00 on a replacement control board.
Third: Suburban's "customer support" is the WORST. Their response to my problem was "We can't help you trouble-shoot any gas appliance, and you can't send anything back to us. You have to take it to one of our "authorized" repair centers for warranty service, which we only pay a flat rate and you're responsible for the rest. Sorry." Good thing I was an electronic tech in a past life, or I would have tossed the whole furnace in the street and bought an Atwood.
Fourth: Use the same BTU rating as the old unit. Don't go bigger or you'll have the unit shutting down. It must have the proper airflow to keep itself cool. Remember, when it's heating, IT'S ON FIRE !!!!
Fifth: I promised the nice lady at Suburban that I would tell everyone I could about their poor customer service. She seemed amused.
So, there you have it.

[litlgeezer]

Idroba, I certainly will entertain your suggestion. The one screw on one corner of the housing, next to the outer water, seems to be impossible to get to, without removing the water pump assembly - and, even the pump assembly is going to be a real chore to remove and replace. Thanks.

[Island Time]

Check this out

[Island Time]

I just did this. I hope the pictures help!

[litlgeezer]

Thank you Edglenn for your informative reply. To save the $$ and the aggravation, I may just settle on replacing the existing catalytic heater. It too, is not working properly. It lights and seems to start working fine. Then, I hear an 'internal' bump sound and the fire immediately begins to die out. Evidently, the gas valve has shut itself off for some unknown reason. Thanks.

[Island Time]

I did use the old box as the plennum. I cut part of the original cover to make the duct transition. I bought my new system from California. Less than 600$ I spent about 8 hours doing the new install. The tools were a great exspense. However, they are tools to be used on other projects.

[edglenn]

Litlgeezer,
I wouldn't want to discourage you from replacing the furnace. They're the best for primary heat. The catalytic unit is fine for backup, but the furnace is the only way to go. I can't say Atwood is any better, I haven't used one.
The "bump" you hear on the catalytic is probably the safety. The heat sensor tube, or thermistor, thinks the flame has gone out and shuts the valve off, depending on what model you have. Pretty simple replacement.

[Randy Gates]

I went through just what you are going through. I have a 1968 Globetrotter and researched the same equipment. I ended up going with a catalytic heater and mounted it higher up where it heats more efficiently. Mine is a 20 foot. These are very safe units, no worry about CO2 with these. Take a look before you invest in the Suburban. Just a thought.
Randy

[edglenn]

Yeah, mine's a '69 Overlander. Love the CAT heater. They work great. Have one in my Mohawk, too.
You DO have to have a small amount of combustion air, however. The CAT does create CO. There's a calculation for the vent area on the Wave site, somewhere. I guess the AS isn't airtight enough to be a problem, but you're supposed to crack a vent!
I think a 2-3" round bird-screen should work, adjacent to the door.
Here's one at my battery compartment (ignore the lack of polish, still in progress!):


I still prefer the furnace. Can set the T-stat, and leave it overnight.

[litlgeezer]

I am considering a 'Northstar' catalytic heater to replace the existing one that's giving me problem. The furnace replacement will still be on my list to do, but the catalytic heater install will be a quick, easy fix for the on coming winter months. Thanks.

[litlgeezer]

Originally Posted by idroba

Probably not. Although the box size may be the same, the new ones have a different electrical connection system, different cooling vent holes for the electronic ignition, and usually a different gas inlet location from the one you have in a '72. The outside inlet and exhaust tubes probably are in the correct location.

I would recommend you consider changing both the guts and the box both. It is not difficult to remove the box, it is generally held in with only two screws in the bottom, near the front. It will slip right out, assuming that you are not one of the unlucky ones with a furnace with a shelf on top of it, and a bar in front of it.

Let us know how you make out.

Apologize for dropping off the radar about the furnace. Haven't tackled it yet - summertime. I did install a new Olympian catalytic heater and it worked well for the 'cool' winter nights here in the south. I do want to revisit the furnace eventually, just too many other higher priorities right now. One thing I have learned is to take the challenges at a moderate pace, one at a time. Otherwise, it turns into work.

[nickclifford]

Originally Posted by litlgeezer

I'm sorry, but I thought this might be an appropriate jumping on place. I am a new member who recently acquired a 1972 Int'l Sovereign. I probably paid too much for it ($6,500) as I have found a few items that need repair or replacement. I removed the Suburban NT-30 S furnace after finding that the burner tube was rusted out. A factory Airstream tech emailed that a NT30SP was the correct up-grade for it. Because of the very tight space next to the original water pump, I decided not to remove the furnace housing. Instead, I want to purchase another furnace and insert the new 'guts' into the existing housing. Can anyone tell me for sure that the 'guts' of the new NT30SP will slide into the existing housing AND match up to the exterior inlet/exhaust holes? Thanks for any helpful responses you can offer.

Hi ... how did that work out? seems like these replacements with 30K BTU are 23" deep and space is only 22" ..?