My Allegro BUS 39 is a 1999 model with a basement furnace. I started it up and found that it operates fine, however, understanding how it operates is a bit confusing to me. I posted several pictures in hopes that someone can help me understand it. The furnace sits in one area, what appears to be some kind of distribution box in another. The pictures became mixed up when I posted them so please forgive me if the descriptions are out of order relative to the pictures.Hole in the floor behind couch. I believe there should be a register grate there but none found. One large heat discharge line laying in there and one small perhaps 1.5" flexible line in there which comes from the distribution manifold mounted under the stovetop. An external fitting coming from the distribution manifold under the counter stovetop area. I did not notice any heat coming from this as I do the one mounted to the furnace door. Another picture shows the external fitting coming from the distribution manifold under the counter stovetop area. I did not notice any heat coming from this as I do the one mounted to the furnace door. Intake(?) and exhaust for the furnace which is below the floor as described above.

You have 2 furnace's.The FIRST top pic is the "rear" furnace and heat duct hoses that supply heat from the rear to the kitchen area. The 2nd pic from top shows the 2nd furnace outside exhaust and intake for the FRONT area of the RV. This heats the driver cockpit area and the area about 10 feet back from the drivers area. The 3rd pic down shows the outside rear furnace access and this furnace is NOT in the basement but on the floor next to the refer inside and the backside of the FIRST pic. Yes, at one time Tiffin did install a duct cover, on the last pic showing a duct hose coming out of the floor, but they usually just let the hose blow warm air because it was better to not have that duct blow straight up and hit the bottom of the couch. You have either 2 wall tstats for the furnace operation or you have the Dometic LCD wall 2 stat with ZONE's. Zone 1 and Zone 2. Zone 1 controls the front furnace and Zone 2 controls the rear main furnace. Doug

I guess I need to find the other thermostat and turn it on! I am most grateful for this information as I knew the venting looked like another furnace yet no air was coming out of it so assumed it was perhaps a fresh air intake for the manifold. Guessed incorrectly it seems. Thank you Dougranier!By the way, the small hose on the left side of that second or rear furnace runs to the annular space in the floor around the front furnace. What the heck is that for?

Monkeyrun wrote:I guess I need to find the other thermostat and turn it on! I am most grateful for this information as I knew the venting looked like another furnace yet no air was coming out of it so assumed it was perhaps a fresh air intake for the manifold. Guessed incorrectly it seems. Thank you Dougranier!By the way, the small hose on the left side of that second or rear furnace runs to the annular space in the floor around the front furnace. What the heck is that for?Does your tstat have a LCD display or Black tabs and a temp slider? Take a pic of your tstat and post it. Doug

They run a duct to the basement to keep the plumbing from freezing. That could be what the duct to the the front furnace is for.

John Wayne wrote:They run a duct to the basement to keep the plumbing from freezing. That could be what the duct to the the front furnace is for.John it's a weird thing because it runs from the left outlet of the front furnace, to outside the sink base cabinet, to across the floor behind the couch, into a hole in the floor and then shows up next to the other large discharge you can see in the floor cutout. That large hose was not sticking up like you see it, I yanked it up in order to take a good shot of it. I have yet to find the hose that heats the basement although I have not started that rear furnace. Will work on that after church today. Pictures of thermostats coming!

Help understanding Allegro Furnace Operation | Good Sam Community

11 Replies

Monkeyrun
Explorer
Oct 09, 2013
Doug, the area in that hole is pretty well sealed up in the basement. My guess is that most of the "cold air" is returned from that large heat outlet which also sits down in that hole, basically recirculating much of the heated air back through the unit. I guess the only thing I can do is to purchase a floor register to put back over the hole. I noticed a style of grate which has a built in diverter that is made to travel beneath a piece of furniture, kind of a snorkel looking thing.

Basement heat, none found. I ran both furnaces and was unable to find any type of heat supply for the basement.
Monkeyrun
Explorer
Oct 06, 2013
I tested the unit under the sink and it works fine. Still trying to figure out where that line that travels from that unit to the hole in the floor SHOULD be located. No luck locating more floor cutouts under the cabinet but much of it I cannot see.
dougrainer
Nomad
Oct 06, 2013
Monkeyrun wrote:
Where is the cold air return on these units? Si that it on the top as seen through the hole in the floor via last picture?

Thanks for the help on this one folks!

Regards,

MR

The cold return for the rear furnace is that access door you removed to show the duct hoses.
The cold air return (front) is both that hole in the last pic you posted and the area inside the basement where it is mounted. Doug
Monkeyrun
Explorer
Oct 06, 2013
Where is the cold air return on these units? Si that it on the top as seen through the hole in the floor via last picture?

Thanks for the help on this one folks!

Regards,

MR
dougrainer
Nomad
Oct 06, 2013
You will have 2 of those wall tstats in the RV. The one closest to the FRONT of the RV controls the front AC and the front furnace. Doug
Monkeyrun
Explorer
Oct 06, 2013
The hose on the floor runs from the left side of the rear furnace, across the floor to the hole in the front where the other furnace lives. That hole is completely sealed from the basement, I just checked again.

I now suspect that the previous, original purchaser of this coach took that line that was supposed to heat the basement and made this Rube Goldberg run so as to avoid running the front furnace most of the time. Having that extra line running to the same place the 6" discharge for the front furnace is located makes absolutely no sense and I have to believe Tiffin would not do such a sloppy job of it.
Monkeyrun
Explorer
Oct 06, 2013
John Wayne wrote:
They run a duct to the basement to keep the plumbing from freezing. That could be what the duct to the the front furnace is for.

John it's a weird thing because it runs from the left outlet of the front furnace, to outside the sink base cabinet, to across the floor behind the couch, into a hole in the floor and then shows up next to the other large discharge you can see in the floor cutout. That large hose was not sticking up like you see it, I yanked it up in order to take a good shot of it. I have yet to find the hose that heats the basement although I have not started that rear furnace. Will work on that after church today.

Pictures of thermostats coming!
John_Wayne
Explorer II
Oct 06, 2013
They run a duct to the basement to keep the plumbing from freezing. That could be what the duct to the the front furnace is for.
dougrainer
Nomad
Oct 06, 2013
Monkeyrun wrote:
I guess I need to find the other thermostat and turn it on! I am most grateful for this information as I knew the venting looked like another furnace yet no air was coming out of it so assumed it was perhaps a fresh air intake for the manifold. Guessed incorrectly it seems.

Thank you Dougranier!

By the way, the small hose on the left side of that second or rear furnace runs to the annular space in the floor around the front furnace. What the heck is that for?

Does your tstat have a LCD display or Black tabs and a temp slider? Take a pic of your tstat and post it. Doug
Monkeyrun
Explorer
Oct 06, 2013
I guess I need to find the other thermostat and turn it on! I am most grateful for this information as I knew the venting looked like another furnace yet no air was coming out of it so assumed it was perhaps a fresh air intake for the manifold. Guessed incorrectly it seems.

Thank you Dougranier!

By the way, the small hose on the left side of that second or rear furnace runs to the annular space in the floor around the front furnace. What the heck is that for?