Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Topic: Atwood Two Stage Furnace Installation in 99' U270 Pt.1 (Read 1121 times) previous topic - next topic

Atwood Two Stage Furnace Installation in 99' U270 Pt.1

April 03, 2019, 06:46:11 pm

I tried every which way but loose to try and get pictures inline with the text at the appropriate part of the narrative but was unable to do so. Too bad, it would have made it easier to follow... I have done before, though it never came out the way I wanted. I looked at the forum manual and found some references, but alas, everything I tried ended up with either a question mark or a completely blank space. Maybe by the next project topic I start, I will be able to figure it out, but for now it will have to be the low tech approach.
The original Atwood 8535-III 35,000 BTU Hydro Flame furnace had been giving us the howling banshee treatment which could occasionally be silenced by percussive adjustment. I knew when contemplating a potentially 10 month trip that this needed to be addressed beforehand. I determined that the motor was shot as the side to side play was about a quarter inch. The burner was also shot and that particular part number is not available. There is likely a replacement that would work, but that decided me to pursue an upgrade. I had long had the Atwood two stage Excalibur XT on my coach upgrade list to replace OEM unit. Unfortunately, since Atwood was swallowed up by Dometic, the Excalibur XT two stage unit had been discontinued. In researching the Atwood two stage furnaces, I discovered that the Excalibur XT was just label applied to one of several two stage variants. These were made in a couple of form factors and various capacities.

At first, my web searches for the Excalibur XT seamed to show product availability from several sources. Starting with the lowest price first, I called or emailed for availability. The response was universal.... "don't know why that is still on our website, but those have been discontinued". To make matters worse, most likely the new single stage units have the gas supply and electrical connections in different places, and the doors were different so our Xtreme painted door wouldn't directly fit.
eBay to the rescue... sort of. I found an eBay listing for a new old stock Atwood 2540DCLP two stage furnace with the required digital thermostat included. The buy it now w price was $799 plus about $70 S&H. I found the seller's website and discovered the same unit there for $699 plus free shipping. The drawback of this unit, besides no warm and fuzzy return policy on the NOS unit, is that the body of it is about 2" taller and 5 inches deeper. The best I could figure by careful measuring, the increased height wasn't too big of an issue, since the part of it that faced the outside tapered down to the same dimensions as our OEM unit. Plus, the gas supply and electrical connection is in the same place as the original. The increased depth however, was more problematic. The drain pipes from the bathroom and the kitchen run through and exit through the bottom at the back of the furnace compartment. It looked like it would just fit, barely clearing the plumbing drain. I went ahead and took a chance and ordered it, after talking the their tech.

The unit was shipped quickly and arrived somewhat damaged. I suspect it was shipped that way because the box didn't have damage in the corresponding location. That didn't leave me feeling happy, but the damage was just some bent sheet metal in the plenum area around the right side outlets and a little in the front around the vent. I decided it was easier to straighten out the sheet metal than to deal with credit card disputes, and we were running out of time to get ready for our trip.

One of the problems with the unit being 5 inches deeper turned out to have more to do with duct locations on the sides being shifted back by that amount. The original configuration used two ducts on each side and three on the back. Since the unit was deeper there was no room for one of the four-inch ducts to wrap around the corner of the furnace and connect on the back. After modifying the kitchen cabinet below the bottom drawer under the cooktop, I used a couple of short (18") aluminum flex ducts to route the ducts clear of the bottom drawer, On the one closest to the toe kick of the cabinet, I attached a 4" splitter so that I could put the nearest outlet in the toe kick under the sink area and the one under the couch closest to the kitchen cabinet using one of the two outlets on the kitchen side of the furnace. The forward most vent (farthest for the furnace) behind the drivers chair used the other outlet. I also made a low profile duct connector to attach to the register in the toe kick under the sink, since the insulated ducting would have been to bulky to make the sharp 90º required.

The other problem with the unit being so much deeper was that the two 2" basement heat ducts go up through the floor right under the rear of the new furnace. Before each of them came up through the floor and did a 90° turn to the back of the furnace where they were attached with Foretravel made 4" to 2" adapters. The new furnace had a removable cover on the bottom rear (this would have been removed and bottom discharge kit would be put in for certain applications, so I just took it off and modified the 2 inch adapters and mounted them on the bottom cover right above the location where the basement ducts come up through the floor. That part of the install worked really well, as it eliminated two 90º bends and about ten inches of 2" flexible ducting.

We store dry food goods in the bottom drawer right next to the body of the furnace and immediately above the ducts. The thin wire reinforced ducting that Foretravel used gets very warm in operation and... heat rises! So I replace the original ducting with some insulated 4" ducting. I had previously replaced the ducting under the couch with insulated ducting when I installed the bamboo flooring. I did this because I keep a couple of guitars under there and I had discovered that the area under the couch got extremely hot while running the furnace, which is bad news for acoustic guitars, or any guitar for that matter. The use of insulated ducting under the couch reduced the temperature from over 110º to about 5º over the temperature elsewhere in the coach. I reasoned that using insulated ducting could only make the furnace more efficient since more of the heat ends up in the space you are trying to heat. That decision did require some modification of the cabinet framework to allow for the greater space required for the insulated ducting. For the 4" splitter, I applied foil baked foam insulation. I also added a piece of FRP as a cover to keep the 'fluffy' ducting from potentially interfering with the function of the bottom drawers.
Don

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #1 – April 03, 2019, 06:58:53 pm

Don,

Your mechanical/engineering skills continue to set the bench-mark for coach ownership!

As with boats, "smart owners" RULE!

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.2

Reply #2 – April 03, 2019, 07:01:04 pm

Part 2.
Since the body of the new furnace is thicker than the old one, I had to fabricate a new mounting system. To make installation from the inside of the coach (the body of the furnace is larger than the opening), I used aluminum angle stock screwed to some wood that I cut down to the appropriate thickness so that the tabs on the outside opening of the furnace would line up with the bezel that door attaches to. This took a bit of trial and error to accomplish so that the tabs would line up with the slots in the bezel and the furnace was square with the opening. The aluminum angle in effect created rails that I could slide the furnace in through the air return grill opening. Side note, I had enlarged the opening and installed an oak grill. With the grill removed, the opening was large enough to fit the furnace easily. The OEM opening would have otherwise been too small and required removing the ¼" plywood panel that the original smaller white metal grill was attached to.

On the bathroom side of the furnace, the toilet pedestal duct had done a 180º U-turn to meet up with the front duct outlet. Not the best option for air flow, but now with the duct outlets on the new furnace shifted 4" farther back (towards the centerline of the coach), the duct would have had to have been extended and made an additional very sharp 90º bend to reach the outlet. To remedy that problem, I used a 4 ¼" hole saw and made a new path that eliminated the 180º and had a straight shot to the duct outlet. One final problem is that the Atwood two stage furnace requires the use of Atwood's digital thermostat. I decided to look at this problem as an opportunity to gain flexibility when heat is required. Both of our A/C units are equipped with heat pumps and the previous set up did not allow for running the heat pumps along with the furnace. It was strictly an either or situation. Not that running the furnace and heat pumps concurrently has been something I have missed, but I like flexibility so I talked myself into it. This required figuring out how to wire the thermostat and running wires to the desired location. I chose to mount it adjacent to the coach information panel. I found a clear space in the storage compartment below the furnace to drill a hole and ran the wire across the coach along the top of the back wall of the basement and up through the floor in the cable chase just forward of the pantry. From there, I pulled back some of the excess communications cable from the old Heart Interface Freedom 20 remote (which happened to be the same type of communications cable as required for my Midnite Solar charge controller remote) and used that as a pull line to pull up three 18 gauge wires for the thermostat through the hollow space of the pantry cabinet wall. Easier said than done, but it worked out.

It wasn't an ezpz pull, but I didn't damage the old Heart Freedom 20 control cable and it got the thermostat wires into the space behind the coach information panel. From there, I had route the last 8" of wire through the inside of the pantry because of some framing that runs vertically in inside the hollow pantry wall. I could have cut out some of the paneling behind the coach information panel and drilled through the obstructing framework, but not enough bang for the buck... and I still had the idea that I might make it to the gathering at the "Q", and so elected take a shortcut here. Also, the thermostat wiring isn't visible inside the cabinet because one of the adjustable shelves happened to be there already. This project turned out to be a lot more work than I originally thought (I know, shocking!). But I piggybacked several projects on this one because of the areas I needed to access. For instance, besides the furnace installation;
Microwave circuit had suffered a short where it comes up through the furnace compartment as a result of some less than careful drilling to run wire for the solar panels (mea culpa). When the old furnace was out, the romex feeding the front A/C appeared to be nicked as well. To remedy that issue, I cut out sections of the damaged romex and mounted a J box under the furnace location where the street side Romex runs and ran a short length of new 12 gage romex for both the microwave and front A/C circuits. I added another junction box behind the fridge and joined the new romex up to the feeds for the front A/C and microwave circuit in the overhead. I had to run wire for the new thermostat, so I also ran some CAT 6 for the Generator EMS display at the same time... oh, and while I was at that, I went ahead and made a new coach info panel and installed the new EMS display. Oh, and while I was at that, the cavernous void under the pantry that used to house the ice maker got a make over that will be the subject of another post. And then there was the new Wolf cooktop installation that needed an electrical outlet added as well as a redo of the gas supply and other projects that escape me at the moment.

There are more pictures in the album by the same name as this topic and, in spite of the length this post, a lot of detail has omitted in the description. I have tried to make the narrative as understandable as possible, but future edits to improve the flow are likely...
Don

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #3 – April 04, 2019, 01:49:37 pm

Don, not only are you a good technician, but an eloquent and voluminous wordsmith. You inspire all of us. Your post was so long that I had SIRI read it to me.

I just installed a two stage Suburban SHD-2542Q heater with an Ecobee 4 thermostat, posted on this forum. Many minor modifications were also required, but it fit from outside the rig. It was also "damaged in shipping", including a cracked fan rotor and fan housing. Fortunately, the seller shipped new parts, but I had to disassemble the whole furnace for the repair. Love it though. I will comment with some pros and cons:

PROS
- You'll love the quite
- You'll sleep better
- Bragging rights for a job well done

CONS
- Fouling of the combustion chamber and igniter. Massive carbon build-up occurs on the low stage setting.
I am not sure if it applies to your model, but Atwood two-stage furnaces have this known problem, hence the discontinuation?
Solution: Just clean out the carbon more frequently.
This is per "red tractor", a knowledgeable forum member and former Foretravel technician.

Again, thanks for the helpful post.

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #4 – April 04, 2019, 02:57:41 pm

Thanks for the kind words! We haven't used it much so far, but what I like about it most is that even on high, it is much quieter than the old one. I may be able to attribute it to the fact that I removed several 90º bends and one 180º in the ducting while rerouting it to fit the new outlet locations. It was a case where a problem became an opportunity... However, I was a little disappointed that while on low, there is a sort of pulsing sound that isn't present at all on high. I have discovered that there is a slight leak in the furnace line and I fear that it may be where the copper tubing comes up through the floor and makes a fairly sharp bend. While the cooktop gas supply that I modified includes a tee, two valves, several flares, a separate regulator for the Wolf cooktop, there is only the two terminal connections on the furnace line. So when Tys with the SSS (super sensitive sniffer) smelled LP under the cooktop, I was sure I must have screwed up on one or more of those connections, but when I capped off the furnace line at the manifold, Tys' noise and the combustible gas sniffer I got verified that the leak was gone. So glad we don't need the furnace right now because I will probably have to take the drawers on that side out and disconnect the ducts on the kitchen side of the furnace to access the furnace gas supply where it comes up through the floor.

Oh well, I never have to wake up in the morning thinking I have nothing to do on any given day...
Don

Quote from: Tim – April 04, 2019, 01:49:37 pm

PROS
- You'll love the quite
- You'll sleep better
- Bragging rights for a job well done
CONS
- Fouling of the combustion chamber and igniter. Massive carbon build-up occurs on the low stage setting.
I am not sure if it applies to your model, but Atwood two-stage furnaces have this known problem, hence the discontinuation?
Solution: Just clean out the carbon more frequently.
This is per "red tractor", a knowledgeable forum member and former Foretravel technician.

Again, thanks for the helpful post.

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #5 – April 04, 2019, 03:17:39 pm

Thanks for the kind words Brett! I have to thank necessity (the mother of invention) for the motivation.

I don't always succeed, but I always try to find the opportunity to improve the status quo when tackling problems. Fortunately, I have a patient and understanding partner who puts up with my obsessions.
Don

Quote from: wolfe10 – April 03, 2019, 06:58:53 pm

Don,

Your mechanical/engineering skills continue to set the bench-mark for coach ownership!

As with boats, "smart owners" RULE!

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #6 – April 04, 2019, 04:46:19 pm

I'm behind you 100%

Gas leaked on mine at first. Had to tighten up some connectors.

I think the term DIY should be changed to: DIA (Do It Again):

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #7 – April 04, 2019, 05:11:11 pm

Only the furnace inlet connection is a possible culprit and I tightened and did a thorough soap check on it before putting the door on, so I am afraid that the copper tubing where it makes a 90º after comes up through the subfloor is the most likely culprit. But before pulling things apart to uncover that, I will try to get a wrench on the flare nut from behind. Then I will hook up the furnace line at the manifold and put my detector to work (didn't have it back then). Unfortunately when I was installing the furnace, I did have to move the copper furnace line around a little (gently as possible!) to position it. It is possible that it has work hardened in 20 years of going down the road and moving it slightly may have been enough to open a crack...
Time will tell and I would be as happy as can be if turns out to be a loose fitting. The alternative is to splice in a section of new copper. I have the fittings and flaring tool with me, space to work is the issue. I may even have to disconnect all the ducting etc. and pull it back out part way to gain access. The rails I installed will make that much easier, but the DIA is a PITA!
Don

Quote from: Tim – April 04, 2019, 04:46:19 pm

I'm behind you 100%
Gas leaked on mine at first. Had to tighten up some connectors.
I think the term DIY should be changed to: DIA (Do It Again):

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #8 – April 05, 2019, 07:05:43 am

After trying to gently move the copper pipe around, I managed to exceed it's bend radius and ended up crimping the pipe slightly. No leak there but it would have leaked if I left bending it. Then I stopped and bent the pipe in another area.

A tube bender would have been useful.

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #9 – April 06, 2019, 12:49:30 am

They make courigated stainless steel tubing for gas. available at the big box stores..a 360 loop in copper does wonders if you have be the room

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #10 – April 06, 2019, 06:02:31 am

I believe copper is preferred to corrugated stainless steel tubing, to avoid cracking from vibration.

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #11 – June 19, 2019, 01:37:43 pm

An belated update to this thread;
We were in a campground in Wyoming and it was getting into the 20's at night (back in May), so I used a 4' corrugated stainless appliance connector with female flares on both ends to replace the last 4' section of copper tubing feeding the furnace. Whether or not copper is the preferred material (opinions on this subject vary, but FOT used copper for LP except to feed the regulator and the the black iron manifold near the tank) for the appliance LP supply in a coach, there was no way to run new copper tubing without removing furnace first, so I cut the copper line just before where it went up through the basement ceiling. Inside the coach after disconnecting the ducting and removing the drawers, cooktop etc. next to the furnace compartment, I cut the copper tubing next to the furnace on the drawer side. I managed to feed the stainless appliance connector underneath the furnace and connected the flare nut to the male flare on the furnace. Down below, I put a ½" flare nut on the cut end of the remaining LP copper feed in the storage compartment, screwed in a male to male ½" flare and fed the stainless appliance connector up through the basement ceiling after removing the huge plug of caulking that sealed around it. After smoothing the edges of the hole, I sealed around the stainless appliance connector with expanding plumbers foam after making sure that it wasn't touching the edges of the hole. I put foam rubber pipe insulation around the appliance connector where it runs under the furnace and where ever it was exposed inside the coach. At some later point, I may pull the furnace and replace the stainless appliance connector with copper, but for now the leak is fixed and the furnace is usable. The only thing about this repair which, as far as I can tell doesn't meet code, is that the stainless steel appliance connector isn't supposed to penetrate a wall or floor. However, I took pains to make sure it can't rub any edges and is cushioned and supported along its length. Both ends of the flexible appliance connector are accessible and I have verified with a combustible gas leak detector (and Tys's nose!) that there are no leaks. I will revisit the issue sometime in the future when we are back from this 9 month trip we are on... maybe

Don

Quote from: Jack Lewis – April 06, 2019, 06:02:31 am

I believe copper is preferred to corrugated stainless steel tubing, to avoid cracking from vibration.

Edit to add a picture to illustrate what a flexible appliance connector is as defined by code.

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #12 – June 19, 2019, 03:53:03 pm

Quote from: Jack Lewis – April 06, 2019, 06:02:31 am

I believe copper is preferred to corrugated stainless steel tubing, to avoid cracking from vibration.

Interesting! I have noticed when visiting the Bluebird forum that their coaches employ copper tubing for almost all the air system lines. Often wondered if it works better than the plastic lines on our coaches in that application.

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #13 – July 07, 2019, 05:04:14 am

I'm disappointed the 2stage furnace isn't manufactured anymore! I was planning to install one in the future.

I did buy the control valve off ebay (NOS cheap) for a 2stage atwood a while back and installed a 2stage fan motor (my motor bearings were shot). I was going to PWM to slow the motor down and put a switch on to use the lower gas flow rate of the 2stage control valve. I wrote a thread about it a while back.

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #14 – July 08, 2019, 06:40:53 am

Ditto. The old furnace manufacturers have not innovated, leaving an entry for Truma:

Truma VarioHeat Comfort | Truma

"near-silent operation and intelligent fan control, complete with a THREE STAGE burner system and special night mode"

Too bad I did't know about Truma prior to installing my 2-stage Suburban heater last year.

Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 11, 2025 ...

Atwood Two Stage Furnace Installation in 99' U270 Pt.1

April 03, 2019, 06:46:11 pm

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #1 – April 03, 2019, 06:58:53 pm

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.2

Reply #2 – April 03, 2019, 07:01:04 pm

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #3 – April 04, 2019, 01:49:37 pm

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #4 – April 04, 2019, 02:57:41 pm

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #5 – April 04, 2019, 03:17:39 pm

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #6 – April 04, 2019, 04:46:19 pm

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #7 – April 04, 2019, 05:11:11 pm

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #8 – April 05, 2019, 07:05:43 am

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #9 – April 06, 2019, 12:49:30 am

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #10 – April 06, 2019, 06:02:31 am

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #11 – June 19, 2019, 01:37:43 pm

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #12 – June 19, 2019, 03:53:03 pm

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #13 – July 07, 2019, 05:04:14 am

Re: Atwood Two Stage Furnace Installation in 99' U270 Pt.1

Reply #14 – July 08, 2019, 06:40:53 am

Affiliate Notice