Furnace blowing out black soot

[mr. seaview]

have a 99 national seaview 8310 model rv. my furnace has always worked
fine for the last 4 or 5 years with no problems. about 2 weeks ago turned on
at night and in the morning i discovered i had ran out of propane sometime
during the night. when i went outside and looked at my furnace vent next to
the door it was covered in black soot. i refilled my propane and turned on the
furnace and again it did nothing but blow out black soot from the exhaust
vent outside the door. i figured the burner assembly needed to be cleaned as
i have never cleaned it or had it cleaned.
i did not know how to get inside the furnace to the burner assembly so i called
a mobile rv service to come out and clean the burner assembly. he cleaned it
out and showed me a lot of black dust and rust and crap inside the burner.
he then tried the the furnace and still t continued to blow out black soot
from the exhaust. he said it needed 2 new parts and that i might be able
to find them on ebay? but he said that even replacing with the new parts
would not guarantee that it would fix my problem. he also stated that in
his 20 years of rv repairs he has never seen a furnace blow out black soot?

any way he suggested the best fix was to get a new atwood /dometic furnace. price of furnace is $1079.00 plus his labor to install new furnace.
so around $1800 total cost. but all units sold out and delivery was 4-6 weeks
anyway i have seen some new atwood furnaces on ebay for around $900
to $1000. when i called him and told him i could get one on ebay delivered in about 4 or 5 days he stated that the furnaces i was looking at on
ebay would not fit and were not interchangeable and would have to be
modified to make them work and would not be any warranty, he ordered
me a new one and told me he would warranty it for 1 year.
i wanted to upgrade to a higher btu furnace but he said it would not fit as
it was bigger in size. my original furnace is 34,000 btu i wanted to upgrade
to a 40,000 btu but he said it would not fit.
so i now have to wait for 4-6 weeks for a new unit.

any thoughts or opinions i believe my original unit is a atwood 8545
hydra flame II model 34,000 BTU
would be nice if i could get a 40,000 BTU to slide into my furnace opening.

i would be willing to pay extra for a 40,000 bTU unit if it would fit???

thanks for any insight or opinions or advice.

[Richard S.]

The 34,000 BTU should be just fine for the size of you motorhome.

[MarvinG]

Black soot would typically be incorrect air/propane ratio. Could be caused by incorrect air flow, wrong size burner office (unlikely since it worked for years), or low or high gas pressure at the burner. If perchance the gas pressure is way off from the regulator at the tank, or other causes, a new furnace may also soot up.

Could also possibly be caused by a cracked heat exchanger in which case a replacement unit is definitely the best way to go.

[Old-Biscuit]

Thing you had a typo....Atwood didn't make a 8545 model

The 8535 was the largest btu furnace in the 8500 Series
*Cabinet size -- 16 1/2"W x 7 3/8"H x 18"D
****8535 is a 31,000btu burner

The 8940 is the largest btu furnace in the 8900 series
*Cabinet size -- 16 1/2"W x 9 1/8"H x 23 1/2" -26"D

8500 Series Info
http://www.rvrepairmanual.com/manual...Flame-8500.pdf

8900 Series Info
https://myrvworks.com/wp-content/upl...LD-Furance.pdf

Even the NEW Models (AFS, AFM, AFL) would not fit
AFL is only one that offers a 40,000btu but it is 16 1/2"W x 9"H x 20"D

Get a NEW Atwood AFMD35... similar size (16 1/2"W x 7"H x 20"D) and is a 34,000btu burner

[mr. seaview]

thank u old biscuit

i hope he ordered the the one u recommended and 34000 btu should be fine

thanks u for your help and recommendation/ thanks to everyone replying

[mr. seaview]

hey old biscuit

i am looking at a AFMD 35141 it is 7"x 16 1/2" x 20" deep it is 35,000 btu
would this work for me without having to change and fittings or connections?
what does the AFMD stand for? thanks again for your help

my current old furnace is a MPD 37582 hydro flame 8500-IV Model

thanks again for your help.

[Old-Biscuit]

Originally Posted by mr. seaview

hey old biscuit

i am looking at a AFMD 35141 it is 7"x 16 1/2" x 20" deep it is 35,000 btu
would this work for me without having to change and fittings or connections?
what does the AFMD stand for? thanks again for your help

my current old furnace is a MPD 37582 hydro flame 8500-IV Model

thanks again for your help.

Your Old Atwood is a 8535 - IV (34000 btu)
Case is a 16 1/2"W x 7 3/8"H x 18"D

The Atwood AFMD is an 'Atwood Furnace Medium size DC Power

AFMD35141 is also 34000btu (don't know why both use 35 designation but are 34Kbtu burners)

1 is LP
4 is Gas Location (Door with pigtail)
1 is Single Gas Valve

131--- Door w/rear gas fitting
151--- Door w/pigtail & rear gas fitting


Although the AFMD is 2" deeper it is 4lbs lighter then the 8535

[mr. seaview]

thank u biscuit

u are correct my current model is a 8535-IV-DCLP 34,000 BTU

Will the AFMD 35141 fit without any modifications?

[mr. seaview]

would it work even though 2 inches deeper? i would probably have to move or modify
something to get it to work?

i will continue to try and call atwood and see what they say? i tried calling all day today
but always kept getting a busy signal.
again thanks for all your help and suggestions hopefully we will figure it out?

[Old-Biscuit]

Atwood AFMD Series Installation Manual
http://techsupport.pdxrvwholesale.co...m-Furnaces.pdf

YOU will have to check out available space vs furnace dimensions and decide YES/NO.

Happy Thanksgiving!

[mr. seaview]

thanks old biscuit

and back at ya happy thanksgiving to u and your family

[mr. seaview]

hey 0ld biscuit

do u or anyone know if atwood/dometic has a website with all their furnace models and
the specs for each model?
i have been trying to call atwood for the last 3 or 4 days and cannot get thru always
rings busy.

if i could just see the different models of furnaces with specs i could possibly determine
which model would be a direct replacement for my 8535-DCLP model.

at least maybe see what options i have for a replacement furnace.

thanks again for all your help and your time.

[Old-Biscuit]

https://www.dometic.com/en-us/us/pro...ns/rv-furnaces