RMD Exhaust Flue

[Parker]

Originally Posted by Ron in BC

Yup, there was a thread on it back in 2015.

I took the opportunity to first heavily insulate the cavity between the baffle and the exterior shell with rigid insulation. Then I fabricated the assembly shown. It created a dedicated path for the hot flue gases to go up and out and the other parts streamline the flow of cooling air.

Ah, okay. I'll go back and dig it out. I agree that it seems to not make a lot of sense to dump exhaust air in a place that we want to keep a cool as possible. I like your design, which might even help when on 120V or towing. Thanks.

[Rossue]

Not everyone has the skill do fabricate what Ron did to completely replace the back wall. When it comes time to pull the fridge for something I will probably do what Klem shows in post #22. Routing hot gasses up & away from the rear cavity and cooling fins makes sense.

[elongest]

Top install 3" dryer duct exhaust chimney. I installed a 3" semi-rigid flexible aluminum duct over the Flue T then leading to the vent screen. Lampro 3" semi rigid aluminum duct, product L301. Bought it from the local Lowes. Flattened one end to abou1.5" wide and cut out one radius about 2" high. Slid the hose over the T used a stick to help position the hose. Put the notched end toward the inboard side of the trailer over the lower side of the T. Once in place you can use a stick inside the hose to get clearance at the high side of the T. It is a tight fit and things stay in place. Then attach the upper end to the screen. Used the complete hose as compressed as possible for support
Result: hot air exits the tube, cooler air exits over the coils. When the vent top is in place the hot air exits the rear of the upper vent. Seems to really thehelp cool down rate on gas. It also helps on the elec. mode
This is just what I did. Take the info. for what it is worth.

[Ron in BC]

Anything that keeps the hot flue gases away from the condenser has to be a good thing.

I think that neat little diagrams with arrows that show the air obediently entering the bottom and flowing compliantly up and out the top are very misleading. The back of the fridge is a minefield of protrusions that work against the smooth flow of air. It's quite possible that some of the swirling air actually carries some hot gases from the flue right to the condenser.

Ron

[Parker]

Originally Posted by elongest

Top install 3" dryer duct exhaust chimney. Flattened one end to abou1.5" wide and cut out one radius about 2" high. Slid the hose over the T used a stick to help position the hose. Put the notched end toward the inboard side of the trailer over the lower side of the T. Once in place you can use a stick inside the hose to get clearance at the high side of the T. It is a tight fit and things stay in place. Then attach the upper end to the screen. Used the complete hose as compressed as possible for support

I really, really like this idea. However, I'm not quite clear on how the hose sits on top of the exhaust tee. How do you prevent the inside wall of the tube from blocking the exhaust tee on one side or the other? I suspect it's in your flattening to elongate the duct, but I don't understand the cutout part and what it does. If it didn't (probably) require pulling the fridge, it would be nice to just remove the tee.

[Ron in BC]

I think the function of the tee is similar to the natural draft hood that you see on the top of conventional water heaters. I'd leave it in place.

I'm pretty sure the slots are to let the bottom edge of the added vent to drop down a little lower. Just getting a dedicated flue down to the level of the tee would be an improvement. Anything lower would be a plus.

Ron

[AK snowbiker]

Some thoughts...

My main concern was recessing the back wall of the baffle so that the exhaust T did not come into contact with the back wall and adding a sheet of galvanized steel to act as a heat sink.

I agree with Ron and others that a dedicated flue directing the exhaust gas away from the coils is a positive step and Klem's solution in post #21 is what I'll be doing next time I pull the fridge. Just be careful what you improvise, there is not a lot of room back there. Scott

[elongest]

The hose sits on top of the boiler and that's what holds it up and in place. The slot in the back was for the lower part the T to get air for the draft, since I was trying to get as much clearance at the output end. Under the T on the output side the bottom is also open and picks up a draft of the excess outside burner heat. I just took a WAG at the slot height since I could not get a measurement. With the uninstalled unit you could get a better Idea on how to arrange the exhaust tube. I can barely see the T much less take measurements with the frig installed.
Eddie

[Parker]

Originally Posted by elongest

The hose sits on top of the boiler and that's what holds it up and in place. The slot in the back was for the lower part the T to get air for the draft, since I was trying to get as much clearance at the output end. Under the T on the output side the bottom is also open and picks up a draft of the excess outside burner heat. I just took a WAG at the slot height since I could not get a measurement. With the uninstalled unit you could get a better Idea on how to arrange the exhaust tube. I can barely see the T much less take measurements with the frig installed.
Eddie

Okay, that's a big help. I was wondering about trying to get enough draft up through the duct, but I also wonder if that's really an issue. So if I understand correctly, you have the lower end of the tee open to allow air to enter, which then exits out the high side but within the new tube. Plus you have additional clearance beneath the high side exit as well. I wonder how much of that is really necessary, since air already enters at the burner. Another way to view this is that one could extend the flue with the 3" duct without introducing any additional air, but maybe that's getting too creative. Plus the extension tube would likely run much hotter that way.

[tractors1]

Inspired idea - I was thinking of a hard tube to do the same thing, but a 3 (or 4) inch of flex dryer tubing is far easier to route and install. I doff my hat toward your brilliant solution.

Not sure any other heat dissipation is needed (as in the sheet metal shield) as aluminum dissipates heat faster than anything except maybe copper - I was considering 1 inch copper piping, but lots harder to install without pulling the fridge.

[Parker]

Eddie, now that you've done this, do you see any advantage (or disadvantage) to using a 4" duct? That would leave more area to pull air in. I'm still curious about how to keep either of the tee openings from being to close to the wall of the duct, but maybe that will sort it self out. I've gotta try this....

[AK snowbiker]

Originally Posted by Old Skool

Some thoughts...

My main concern was recessing the back wall of the baffle so that the exhaust T did not come into contact with the back wall and adding a sheet of galvanized steel to act as a heat sink.

I agree with Ron and others that a dedicated flue directing the exhaust gas away from the coils is a positive step and Klem's solution in post #21 is what I'll be doing next time I pull the fridge. Just be careful what you improvise, there is not a lot of room back there. Scott

Edit: I should of said "Heat Shield" instead of "Heat Sink". Scott

[CoolCampingKid]

Originally Posted by elongest

Top install 3" dryer duct exhaust chimney. I installed a 3" semi-rigid flexible aluminum duct over the Flue T then leading to the vent screen. Lampro 3" semi rigid aluminum duct, product L301. Bought it from the local Lowes. Flattened one end to abou1.5" wide and cut out one radius about 2" high. Slid the hose over the T used a stick to help position the hose. Put the notched end toward the inboard side of the trailer over the lower side of the T. Once in place you can use a stick inside the hose to get clearance at the high side of the T. It is a tight fit and things stay in place. Then attach the upper end to the screen. Used the complete hose as compressed as possible for support
Result: hot air exits the tube, cooler air exits over the coils. When the vent top is in place the hot air exits the rear of the upper vent. Seems to really thehelp cool down rate on gas. It also helps on the elec. mode
This is just what I did. Take the info. for what it is worth.

Wow Elonest! Great simple solution! I have been thinking on a solution for this after I looked down my fridge vent (to inspect for the dreaded charring of the wood back there, mine was clean).

So here is what I have been trying to figure out:

#1 Why did they use a "T" in the pipe? Does this help with heat dissipation or air flow? Could it simply be to keep rain/water out of the flue? Anyone have any thoughts?

#2 Why in the heck did anyone think dumping the warm flue air into the fins of the cooling coils was a good idea? Is this what is the different about the fridges made for cooler climates by Dometic? I wonder if simply re-routing the heat from the flue (like Elongest did) will solve the dreaded fridge cooling issue?

Bill

[PGDriver]

Bill I think the T pipe is intended to hook up to the exhaust kit which is not available here in North America. This would then allow the exhaust to be dumped outside the trailer and bypassing the fins.


Cheers
Doug

[Parker]

I figured it was just to keep crude from falling down into the burner, but that's only a wild guess. The picture Ron posted of the overboard exhaust kit also shows a tee, which is redundant to the one already there, or maybe there are two installation versions, one is tee only (like ours) and the other is tee plus the other stuff to vent overboard.

[elongest]

The 3" duct is really tight but you can move it around a little to get it in there. I looked at 4" duct but I did not think I could get it in there through the top vent. I wanted to route the heat to the vent screen to exit. I tried to get as much air entering the duct as possible. I did not want to increase the draft through the boiler flue. My main starting issue and still is the no or little cooling while on the road.
Eddie

[Ron in BC]

Originally Posted by CoolCampingKid

Wow Elonest! Great simple solution! I have been thinking on a solution for this after I looked down my fridge vent (to inspect for the dreaded charring of the wood back there, mine was clean).

So here is what I have been trying to figure out:

#1 Why did they use a "T" in the pipe? Does this help with heat dissipation or air flow? Could it simply be to keep rain/water out of the flue? Anyone have any thoughts?

#2 Why in the heck did anyone think dumping the warm flue air into the fins of the cooling coils was a good idea? Is this what is the different about the fridges made for cooler climates by Dometic? I wonder if simply re-routing the heat from the flue (like Elongest did) will solve the dreaded fridge cooling issue?

Bill

Originally Posted by Parker

I figured it was just to keep crude from falling down into the burner, but that's only a wild guess. The picture Ron posted of the overboard exhaust kit also shows a tee, which is redundant to the one already there, or maybe there are two installation versions, one is tee only (like ours) and the other is tee plus the other stuff to vent overboard.

Post # 86 guys. It serves the same function as the draft hood on the top of a hot water tank.

I also saw a comment about extending the height of the tee. OK for a few inches but you have to be careful about stuff like that. There's a reason that different flue sizes are specified for other applications.

I think that the use of the aluminum dryer vent is a great solution for those folks that don't want to pull their fridge out and do a more comprehensive mod.

Ron

[CoolCampingKid]

Originally Posted by Ron in BC

I think the function of the tee is similar to the natural draft hood that you see on the top of conventional water heaters. I'd leave it in place.

I'm pretty sure the slots are to let the bottom edge of the added vent to drop down a little lower. Just getting a dedicated flue down to the level of the tee would be an improvement. Anything lower would be a plus.

Ron

I am not certain why a "T" type vent is on some conventional water heaters that is why I asked. Bill

[Ron in BC]

There aren't "tee" type vents on hot water tanks but the function is the same.

At any rate this is a situation where doing almost anything that reduces the inefficient flow of air in that area is an improvement.

Ron

[Vermilye]

While I could be wrong, I believe the "T" is there to prevent a venturi effect caused by wind when traveling from blowing out the flame. As previously mentioned, the "T" is part of a kit used in Australia & other hot areas that vents the heater to the outside. This PDF shows how it is installed.