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-   -   Plus/minus of going with a larger furnace (http://www.airforums.com/forums/f427/plus-minus-of-going-with-a-larger-furnace-2780.html)

Guitars 12-08-2002 09:16 PM

Plus/minus of going with a larger furnace
 
The inspection (and lighting I assume) cap on my 22 foot '67 Safari has rusted off. If the furnace is that rusty it is time for a replacement. (Life is short enough already). The question; the original furnace (Surburban NT-22) is rated at 16,800 btu if I recall. The NT-22 has been discontinued. There is a NT-24 (24,000 btu) and a NT-34 (34,000) that should be fairly easy replacements. The boxes are the same size and either should heat the A/S well. The NT-22 draws 3.5 amps and the NT-34 draws 7.5. The prices are very close. So the question; other than the increased amps the NT-34 draws and the slightly higher price is there a downside to going with the larger furnace? I am guessing the propane useage will be near the same to heat the same volumn of air to the same temperture. The larger one may just do it quicker. Am I missing something here?

Inland RV Center, In 12-09-2002 08:44 AM

Furnace
 
The replacement furnace for your 22 fooot Airstream is Suburban NT30SP. It is also electronic ignition.
However, regardless which furnace you choose, special installation instructions must be followed, so that you can continue using the built in heat ducts, which must be used if you wish to have freeze prevention for the water lines and holding tank.


Andy
inlandrv.com
airstreamparts.com
airstreamcandy.com

Guitars 12-09-2002 10:38 AM

Thanks Andy. That was my gut feeling but I wasn't sure since the NT-30 has a btu rating of about twice the original.

74SovereignInt. 12-09-2002 11:05 AM

difference in requirements
 
Guitars, keep in mind that newer furnaces may have different requirements than their older counterparts.

I may need to change my '74 NT32A due to a ruined burner pilot. While speaking with Suburban they mentioned that a new unit would be different in size requiring some shimming as well as requiring three or for vents as opposed to the two that I currently have. That was not good news as far as I was concerned.

wb13798 12-09-2002 05:26 PM

i also talked to suburban . i wanted to put a nt-40 in place of the nt-30 . physical size was the same not a problem, however the nt-40 furnace require four ducts i have three for the nt-30. the side and top clearances required , i could not get without modifying the cabinet . i stayed with the nt-30. too much work, the shell around the furnace puts of a lot of heat. i would insure that you have the recommended spacing. might have a weinne roast. dont need that.

JPAIRSTREAM 12-09-2002 05:58 PM

I feel you have to keep in mind with a larger furnace you may or may not need as stated above, “more ducts.” Please read the required installation on each furnace you are looking at. The reason is simple airflow leaving at a slower rate then specifically designed will cause the high temp limit switch to shut gas off prior to the living area actually getting up to temperature and causing the furnace to run more often. The complete opposite can happen when you have too much airflow coming out. The air is passing thru the heat chamber so fast its not getting up to temperature and furnace is blowing out colder air. Causing furnace to run for longer periods. This happens sometimes when you put a smaller B.T.U. furnace in then the ducting that you already have ran.

Both of the described above will cause you to use more propane then you really want to use.


As Andy stated NT-30 is the suburban to use.

barbwire 12-09-2002 09:58 PM

Andy, I have a 20 foot Argosy Minuet that will need a new furnace soon. Right now it has a Suburban NT-16 which has an input of 16K and an output of 12.8K. A bit premature, because I think I can make it through the winter, but what new heater am I looking for.

The twenty foot Argosy has rear bath and curb sink. The furnace is right next to the shower. The plumbing runs through a formed plastic vent that skirts the wall around the shower and ends up at the black water tank. The opening that caries the sink drain and supply lines that seperates the kitchen from the bath was glued shut, but I removed the glue. I have an option here of increasing the size of the opening. I have all the kitchen removed for repair, and I can now make the opening between the shower and furnace compartment a bit larger (maybe 50%). It's cold in Montana, should I increase this hole. I know this is a hard question. Just trying to see if anyone has done stuff like this. I hope that is clear. I should have just put in a picture. :)

Thanks,

barbwire

eracism 01-06-2003 06:23 PM

Larger furnace
 
I just replaced the original Suburban furnace in my 1963 Tradewide with the same size. I am presently using the trailer at 9200 feet elevation in high winds. If I put the setting at any
higher then just past the off position, it drives me out.

darryl97420 11-28-2011 07:51 AM

This is an old thread but worth bringing up and asking a question.

Andy, In this thread you stated that the NT30 is the proper replacement but the OE was the NT22, same as my Argosy28. I have access to a freshly serviced NT34SP. Will that be a suitable substitute for my Argosy? If so, what changes if any to the duct work will need to be made? Currently there are 2 ducts being used, one for the front lounge the other goes to a box under the street twin then to the tanks.

Thanks,

Darryl


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