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Old 01-20-2021, 04:18 AM   #1
gwilkrrs
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suburban furnace?

I had a suburban sf30f that was destroyed in a tire blow out and am looking to replace. I cant seem to get a handle on what the numbers mean- I am looking at a sf35fq and don't know if its compatible?
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Old 01-20-2021, 05:24 AM   #2
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Specs of the two dimension wise ..
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Old 01-20-2021, 05:29 AM   #3
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so if on the sf30f the f is for front gas I wonder what the fq stands for-
I will look for pics to see where the gas is on that one.
thanks!
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Old 01-20-2021, 05:32 AM   #4
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Numerical numbers....size of burner in BTU

F===front gas connection
Q===QUIET (plastic blower wheels/squirrel cages)
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Old 01-20-2021, 05:34 AM   #5
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SO to answer your question the SF35FQ will fit dimension wise, front gas connection same as your original and 5000 more btu.. the cage wheel on newer units is made of non metal material for quitter operation...

My Alpine has an SF42FQ in it
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Old 01-20-2021, 05:44 AM   #6
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More Info for you

https://www.airxcel.com/rv/suburban/furnaces/sfq-series
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Old 01-20-2021, 12:02 PM   #7
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SO to answer your question the SF35FQ will fit dimension wise, front gas connection same as your original and 5000 more btu.. the cage wheel on newer units is made of non metal material for quitter operation...

My Alpine has an SF42FQ in it
If the ductwork is sized for the lower btu furnace, you may have problems with it overheating if you go up 5000 btu ‘s
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Old 01-20-2021, 12:28 PM   #8
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For the OP going from an SF30 series to SF35 series wont require any additional duct work for minimum requirements per the installation manual
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Old 01-20-2021, 03:52 PM   #9
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For the OP going from an SF30 series to SF35 series wont require any additional duct work for minimum requirements per the installation manual
I see... no additional return required...what does it say about supply’s?
I’ve read so many posts with guys having furnace problems and the guy with the furnace cycling on limit that I’d be Leary about changing any variables. 5000 Btu’s doesn’t seem like a lot but on small furnaces like this it can have an effect on plenum temperature.
I was just offering that because if you have a furnace on the hi side of the design parameters and then you go and add 5000 btu s to the mix it can have consequences.
I’ve been doing hvac for 36 years and in business for over 20 years..people all the time want me to just put a new unit in that is much bigger then what was in the house.
I have to look at the duct system and see what it is sized for to determine if duct need to be increased or additional returns . Usually sized wrong from the beginning as many installers did not do manual j heat load calculations to properly size ductwork and equipment size.
BUT that being said ....it looks like most hvac installations on rv’s are just kinda suggestions and winging it as far as design standards go
lol
I keep trying to think like a hvac guy...I have to get used to the rv way
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Old 01-20-2021, 05:59 PM   #10
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From Dometic/Atwood manual... the output size of ducts and required number of ducts is exactly the same for a 30K or 35K btu furnace
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Old 01-21-2021, 03:52 AM   #11
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thanks all-

this all has been super helpful- price wise is why I am looking at the 35 instead of the 30. the units are expensive new and I found a 35 scratch and dent that comes tested for a fraction of the cost.

I will have duct work to deal with as some flex got destroyed but I haven't started to source that either.....
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Old 01-21-2021, 03:53 AM   #12
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From Dometic/Atwood manual... the output size of ducts and required number of ducts is exactly the same for a 30K or 35K btu furnace
I think your missing my point...I’m not personally saying your wrong so you don’t have to keep showing pages from the furnace manual.
I’m talking about REAL world operating characteristics of furnaces in general.If you have a furnace that is operating on the edge of its design parameters ( high end) as far as ducts are concerned and you INCREASE the btu’s then you can and will see a difference somewhere.
All I said is that he MAY have a problem going forward with having to add ducts or return.
He may not ....but to just make a blanket statement that nothing will happen because the book says so is not very helpful IMO.
The book also says if you look at the note under supply sizes that you may have to add ducts.
AND the first page in book you posted said 55in sq return and the second page you posted listed 65in sq
It seems like the 1/2 ton towable statement rv company’s talk about,you can write it down somewhere but the realworld can prove otherwise.
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Old 01-21-2021, 03:58 AM   #13
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thanks all-

this all has been super helpful- price wise is why I am looking at the 35 instead of the 30. the units are expensive new and I found a 35 scratch and dent that comes tested for a fraction of the cost.

I will have duct work to deal with as some flex got destroyed but I haven't started to source that either.....
Your welcome ...didn’t mean to turn it into a bickering match lol
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Old 01-21-2021, 04:40 AM   #14
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thanks all-

this all has been super helpful- price wise is why I am looking at the 35 instead of the 30. the units are expensive new and I found a 35 scratch and dent that comes tested for a fraction of the cost.

I will have duct work to deal with as some flex got destroyed but I haven't started to source that either.....
In Baltimore if you look at RE MICHEL hvac supply’s you may be able to buy the ducts there. Look up online what you need and when you get to the store walk-in with an air of confidence but not arrogance....don’t ask them any questions about anything because they don’t give advice to people not in the business...when they ask what company your with just say “a cash account “ or “just paying cash “and there is a 60/40 chance they will just sell you what you need as long as it’s just ductwork. They won’t sell you any equipment or anything technical. Act like your just going to buy donuts and have your order ready.
If you have a deer in the headlights look they will send you on your way
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Old 01-21-2021, 04:50 AM   #15
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Kinda like this
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Old 01-21-2021, 09:03 AM   #16
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The OP has asked a question about furnace size difference between SF30 and SF35... I have provided more than enough info for him to make a decision based on facts from the service manuals from both Atwood and Suburban..

The info clearly states the return and duct requirements.. And, as I have stated and shown with the INSTALLATLION specs from the people that build the furnace units and specify their install requirements... there are NONE...

I trust the OP can make a wise choice and if I were buying a new furnace Id be buying the SF35 series based on lower cost and same install spec requirements.

The amperage draw from the slightly larger blower motor is a tad different but certainly not a factor in my opinion...
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Old 01-21-2021, 09:40 AM   #17
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The OP has asked a question about furnace size difference between SF30 and SF35... I have provided more than enough info for him to make a decision based on facts from the service manuals from both Atwood and Suburban..

The info clearly states the return and duct requirements.. And, as I have stated and shown with the INSTALLATLION specs from the people that build the furnace units and specify their install requirements... there are NONE...

I trust the OP can make a wise choice and if I were buying a new furnace Id be buying the SF35 series based on lower cost and same install spec requirements.

The amperage draw from the slightly larger blower motor is a tad different but certainly not a factor in my opinion...
Well then thanks for clearing up how furnaces operate. If I need someone in the future to collate furnace manuals off the internet I know where to come ..and with that ..Have a good day sir
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Old 01-21-2021, 11:07 AM   #18
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Well then thanks for clearing up how furnaces operate. If I need someone in the future to collate furnace manuals off the internet I know where to come ..and with that ..Have a good day sir
Normally I wouldn't play this game.. but heck..

You asked about return and outlet duct sizes yourself and I provided the data directly out of the install manual...

I've removed and replaced well over 50 RV furnaces over the last 45 years.. I am not a certified HVAC Tech..
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Old 01-21-2021, 11:13 AM   #19
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Normally I wouldn't play this game.. but heck..

You asked about return and outlet duct sizes yourself and I provided the data directly out of the install manual...

I've removed and replaced well over 50 RV furnaces over the last 45 years.. I am not a certified HVAC Tech..
Yeah I’m a little grumpy today .. I just know that things aren’t always what they are just because someone put it on paper. If that were the case then diagnosing problems wouldn’t be hard at all. I tend to look at all variables. Anyway didn’t mean to start a “ thing” over this..my apologies
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Old 01-24-2021, 03:47 PM   #20
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I dealt with the same situation last fall.... though i am still completely puzzled by just a piece of osb protecting the furnace from the notorious china bombs... that said the only difference between the sf30f and the sf35 are the unit weight and required voltage.... sorry i have extensive screenshots of the differences but for the life of me i cant figure out how to post them. The 25 30 and 35 all are the exact same measurement air intake and ductwork wise but the 35 requires .5 more amps
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