RMD Exhaust Flue

[tractors1]

Originally Posted by Parker

Okay. I might consider it. I'm still concerned about how the tee sits within the duct when I read about squashing the tube some to get it to fit over it. What keeps the tee centered in the duct so that either exit doesn't end up sitting against the inner wall?

The T will not wind up centered in the duct. When you smoosh the tubing, it's an elongated oval with sharp bends, so the T won't be up against a flat wall.

The tubing is semi-flexible until you smoosh it, then not so much.

Initially I used foil covered dryer tubing to see it it made much difference, which was much easier to install. However, the foil is laminated with poly film - I was able to cause it to flame with a lighter as a test. I switched to the semi-flex aluminum as it has a UL rating good to 400F. None of my readings exceeded 300F.

I started on electric - when I put my hand on either side of the T I could feel warmed air flowing out of both sides of the T. Although it's inclined at the top, the flow is not from the low side to the high side as I would have thought - as theory would have it.

[Klem]

FYI - this is an update of a post a few years ago.

While thinking about the flue I noticed the side vent was larger on some trailers. I didn't want to cut into the side and decided a cool air pickup under the trailer should help balance the overall air intake. The "pickup" is actually a stainless bowl I trimmed.

I have no problem running on propane regardless of speed, wind gusts, etc.

And the RML and now the RMD run better overall with the cool(er) air pickup. I did add a fan above the air box but can't find a picture at the moment.

[Rossue]

Hi Klem- this looks pretty amazing; can we bring you out of retirement? "Klem's Little Shop Of Fixing ETI Fridge Horrors"?

[tractors1]

Klem, this had to take a LONG time!

[Santiago]

Klem, this is classic thinking out of the box.
I love your design. Let's hope it solves the fridge problem once and for all.

Great work Klem.

[skiman]

The latest posts got me thinking about my RMD. I removed the cover and I have a singed spot on the plywood too. The high side of the T is about a 1/4" from the plywood.and facing toward the coils. Makes you wonder what the were thinking. I will probably go with the 3" dryer vent. I like the performance improvement talked about.

Another question. Looking back into the top of the Frig, I see fiberglass insulation on the sides but none on the top. Should there be some batt insulation in there? If I perform sugery, that would be the time to add it. Hi

[tractors1]

Originally Posted by skiman

Another question. Looking back into the top of the Frig, I see fiberglass insulation on the sides but none on the top. Should there be some batt insulation in there? If I perform sugery, that would be the time to add it. Hi

The outfit that replaced my fridge with the RMD displaced the roof liner material over the fridge and refastened it - kind of a crappy job as the old liner has staples sticking out all over it, but it is pretty securely fastened so I didn't take it apart to add insulation. Figure that's an off-season job for when I do pull the fridge.

This mornings readings on electric after moving the thermostat off the fins and putting it in the rear corner against the wall are most encouraging. With a low ambient of 68 degrees last night shows a low of -5F on the freezer and 25F on the fridge (panel setting on max bars) so I'll see where it gets to today. Fridge side in full sun and 100F predicted.

[Rossue]

Originally Posted by tractors1

The outfit that replaced my fridge with the RMD displaced the roof liner material over the fridge and refastened it - kind of a crappy job as the old liner has staples sticking out all over it......

Hey Charlie, wasn't that Camping World that did that that fridge swap for you?

[tractors1]

Originally Posted by Rossue

Hey Charlie, wasn't that Camping World that did that that fridge swap for you?

Yup, but they did ok on the rest of the changeout. Just not as professional as I would have thunk, although few owners would ever notice. Grade of C+ overall.

[tractors1]

Ran the RMD for 48 hours with various combinations of fan/no fan, thermister relocations, taped the hole in the fridge door, water in the drip cup, and added foam to the freezer door. No air conditioning, but the roof fan was open and set to auto (turns on at 76 degrees) and that ran most of the day.

Last night (68 ambient) Freezer low of -5F, fridge at 25F
Today (99 degrees, full sun on the fridge sidewall) Freezer 6F, fridge 34F. Basically a 10 degree differential for both parts with a 30 degree difference in ambient temp. Looking good so far!

Switched over to propane for the next 48 hour run. Adding a fudge bar to the freezer as a test device for wifey. Beer was good and cold today!

[Klem]

Originally Posted by tractors1

Klem, this had to take a LONG time!

Thanks all. I wanted to install a microwave under the frig and while staring in the hole came up with the bottom vent idea. I had pulled the frig and sent it to a frig rebuild specialist in Arkansas.

So the answer is 'yes' it took a while to do but actually I was in the cavity working already ... and it turned out to be well worth the time. The RML did work better, more stable and a bit cooler. And "my" RMD appears to have less bad habits then many of yours. : )

[tractors1]

Finally found a post on casitaforum about a hard pipe flue extension. I crossed paths with Gene, the webmaster for the forum a year or so ago and he mentioned adding a pipe after removing the "T" from his Dometic fridge. This allowed him to easily use a 2 inch aluminum preheater hose to get the exhaust above the fins on the fridge. I'll do this when I pull the fridge to insulate this winter. Dometic sells extension pipes in Europe and OZ.

Post #120 here:

https://www.casitaforum.com/invboard...better/?page=8

[tractors1]

Project summary:

RMD (replacement) fridge freezer usually at 14-20 F in shady forest camping, fridge section often at 39-43.

Forum reports of a scorched wood panel against the outside wall that troubled me and the posting of adding a flue extension using 3 inch semi-flexible aluminum hose. Installed hose with no modifications other than collapsing to wedge through the back side fridge piping. Bottom of hose is about 2 inches below the "T" on the Dometic boiler exhaust pipe. Not fully seated on the boiler shroud.

Did 4 days of testing during unusually hot weather (for Oregon.) Ran the RMD for 48 hours with various combinations of fan/no fan, thermister relocations, taped the hole in the fridge door, put water in the drip cup, and added foam to the inside of the freezer door. No air conditioning, but the roof fan was open and set to auto (turns on at 76 degrees) and that ran most of the day.

With the changes, the fridge was consistently 10 or more degrees colder than before, even with hot weather and full sun during my tests. Not really a solid test against shady forest conditions, so I'll be doing those next week for a valid comparison. Definitely works much better.

1st Run Using Electric Power:

Overnight - (68 ambient) Freezer low of -5F, fridge at 25F.
Late afternoon - (99 degrees, full sun on the fridge sidewall) Freezer high of 6F, fridge 34F.

Roughly a 10 degree differential for both parts with a 30 degree difference in ambient temp.
------------------------------------------------------
2nd Run Using Propane Power:

Overnight - (70 ambient) Freezer low of -2F, fridge at 26F
Late afternoon - (105 ambient) Freezer high of 7, fridge at 38

Another 10ish degree differential but with a 35 degree difference in ambient temp.

[skiman]

Originally Posted by tractors1

Project summary:

RMD (replacement) fridge freezer usually at 14-20 F in shady forest camping, fridge section often at 39-43.

Forum reports of a scorched wood panel against the outside wall that troubled me and the posting of adding a flue extension using 3 inch semi-flexible aluminum hose. Installed hose with no modifications other than collapsing to wedge through the back side fridge piping. Bottom of hose is about 2 inches below the "T" on the Dometic boiler exhaust pipe. Not fully seated on the boiler shroud.

Did 4 days of testing during unusually hot weather (for Oregon.) Ran the RMD for 48 hours with various combinations of fan/no fan, thermister relocations, taped the hole in the fridge door, put water in the drip cup, and added foam to the inside of the freezer door. No air conditioning, but the roof fan was open and set to auto (turns on at 76 degrees) and that ran most of the day.

With the changes, the fridge was consistently 10 or more degrees colder than before, even with hot weather and full sun during my tests. Not really a solid test against shady forest conditions, so I'll be doing those next week for a valid comparison. Definitely works much better.

1st Run Using Electric Power:

Overnight - (68 ambient) Freezer low of -5F, fridge at 25F.
Late afternoon - (99 degrees, full sun on the fridge sidewall) Freezer high of 6F, fridge 34F.

Roughly a 10 degree differential for both parts with a 30 degree difference in ambient temp.
------------------------------------------------------
2nd Run Using Propane Power:

Overnight - (70 ambient) Freezer low of -2F, fridge at 26F
Late afternoon - (105 ambient) Freezer high of 7, fridge at 38

Another 10ish degree differential but with a 35 degree difference in ambient temp.

Bought my 3" ducting yesterday. On the list for today.

[skiman]

Originally Posted by skiman

Bought my 3" ducting yesterday. On the list for today.

Done. The discharge is warm and pretty close to the plastic vent cover up top. Hopefully it won't distort the cover.

Getting the 3" doct in place was a real pain.

[padlin]

Carl, do you mind describing what you had to do?

[tractors1]

Originally Posted by skiman

Done. The discharge is warm and pretty close to the plastic vent cover up top. Hopefully it won't distort the cover.

Getting the 3" doct in place was a real pain.

Yup, I've some healing scrapes from the job. My duct ends maybe 1/4 inch under the mesh wire on the cover base. I checked the topside cover temp right over it while running on propane; only 109F in full sun. The front end of the cover measured 107F, so I figure it's good to go.

When I pull the fridge to add insulation this winter I'm going to replace the flex with a hard pipe flue extension that ends just above the fins, then use 2 inch semi flex that will slip over that much easier.

[skiman]

Originally Posted by padlin

Carl, do you mind describing what you had to do?

I did it as described in post 108 except I did not notch the flex pipe. Left it whole as tractors1, but also made it difficult to get the duct over the T. Sweat a lot and the duct is a bit on the ugly side.

[padlin]

Originally Posted by skiman

I did it as described in post 108 except I did not notch the flex pipe. Left it whole as tractors1, but also made it difficult to get the duct over the T. Sweat a lot and the duct is a bit on the ugly side.

Did you remove the lower part of the roof vent or cut the screen?

[skiman]

Originally Posted by Kountrykamper

I had a machine shop make mine. They made it out of some scrap they had laying around. Hard to say how much it helped because I did so many other things at that time.

If I was pulling the Frig, I would do this. The only thing I would turn the T a bit sideways to get it away from the plywood and trailer wall. I think this would induce a nice draft with the boiler heat introduced above the coils.