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Old 12-08-2010, 09:38 PM   #43
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Most of you folks posting on this thread seem to be staying in areas much colder than we do. We seldom stay where it gets below freezing. We sleep under a down comforter, and don't care to sleep in a room that is real warm. Therefore, the bed area of our trailer is seldom colder than we want for sleeping. I turn the furnace off when we retire. If it is cold in the morning, I turn the furnace back on until I start cooking breakfast. When I start cooking, the place usually gets warm enough to turn the furnace off.

Still like the bath warm for a shower. Feels good.

Been hungry, been broke, and been cold. Don't like any of those things.
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Old 12-08-2010, 09:56 PM   #44
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I thought that the "vinyl over a spring" ducting had a higher resistance than the steel ducts, plus was more likely to gather dirt?

Turning to sports... In my '74, the ducting seams are sealed with what looked like paper with glue that dried out probably a year after installation. It leaked air like crazy.

Also, I noticed that where it passed under one of the singles in the middle sleeping area, there was a large round hole in the top (maybe 3"D) which might have been covered at one time by a slightly larger round metal disc I found on the floor near it. To warm my bed? ::shrug ::

Lastly, when I removed the original orange shag in the rear bath, I temporarily removed the vertical luan piece (that served as the skirt for the tub). The mouth of the duct that had an register fastened to that same skirt with another large hole in it. I suppose that this hole served to warm the area below the tub.

All these items served to reduce the airflow to the register in the bathroom to nearly zero. When I patched and closed the various openings, I was able to have a warm bathroom.

My point is, do you think that anything along these lines could be happening in your newish trailers?
I can see most all of my duct work, except the short length under the shower to the bedroom. It all seems well sealed with flexible duct tape at all connections. The only "leak" is the small branch which feeds the water tank areas. I can't remember if that is off the branch to the bath or the bedroom though. I think its off the bath run.

There is a spot where the BR duct enter the under shower area where the 4" duct is squeezed down to fit through the shower wall. This introduces some restriction.
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Old 12-08-2010, 11:10 PM   #45
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I did some checking and I don't think there's enough clearance to utilize the insulated ducting to good effect.

Aage the vinyl-over-spring ducting is what the factory uses now. The stuff I linked to just has a thin layer of fiberglass and another layer of vinyl. The air resistance is similar.

It's 0 out and I'm running some tests tonight to see whether with the furnace only the bedroom temperature eventually comes up. I'll use that as a baseline.

One thing to watch with the various fan strategies is that the bedroom duct has a T that goes to a small duct to the holding tanks. If a fan is placed in the bedroom this could lead to no airflow or reverse airflow in the holding tank duct leading to freezing problems. If adding a fan I would place it in the area below the closet just on the furnace side of the T.
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Old 12-08-2010, 11:24 PM   #46
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It's 0 out and I'm running some tests tonight to see whether with the furnace only the bedroom temperature eventually comes up. I'll use that as a baseline.
Hi, I did that once for about a week.
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Old 12-09-2010, 09:36 AM   #47
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I did some checking and I don't think there's enough clearance to utilize the insulated ducting to good effect.

Aage the vinyl-over-spring ducting is what the factory uses now. The stuff I linked to just has a thin layer of fiberglass and another layer of vinyl. The air resistance is similar.

It's 0 out and I'm running some tests tonight to see whether with the furnace only the bedroom temperature eventually comes up. I'll use that as a baseline.

One thing to watch with the various fan strategies is that the bedroom duct has a T that goes to a small duct to the holding tanks. If a fan is placed in the bedroom this could lead to no airflow or reverse airflow in the holding tank duct leading to freezing problems. If adding a fan I would place it in the area below the closet just on the furnace side of the T.
Good Idea, I thought of that "sucking" the air way from the tank duct, but I though I remembered it branching off of the bath duct. Pushin it would help the bedroom AND the tank area.
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Old 12-09-2010, 11:19 AM   #48
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I spent the night in the traylah last night and contemplated the problem.

My current thinking is that there should be enough room to run a separate 2" duct for the holding tanks from the furnace back thereby eliminating the need to T off the bedroom duct. This should result in a considerable improvement in heat delivery to the bedroom. It may also be possible to work in an additional 2" duct, again from the furnace back, open in the air space behind the shower. Warming up this area in that fashion would help keep the bathroom warm and would reduce the cooling effect on the bedroom duct.

The rated BTU/h output of the furnace is 26,000 BTU. The delta-T is around 100 degrees with the formula btu=1.08 * dt * cfm and some algebra the total airflow must be around 250 cfm. With four 4" outlets and one 2" outlet (with a quarter the airflow of the others) there's around 60 cfm per duct 4".

Because the delta-t is lower (45) at the bedroom outlet due to conductive losses, and because it only gets 80% of the airflow, due to the T for the tanks, it only gets around 2300 BTU/h (60 * 45 * .8 * 1.08). I think there's a heating shortfall of around 2500 BTU/h because if I put an electric heater back there on 750 watts things even out pretty well.

Adding the two 2" ducts should bring up the airflow somewhat and should also increase the delta T. I would expect it to come up to 65 degrees, which is what the bathroom area gets, (70+65 = 135, I measured 134), around 4200 BTU/h or 1900 BTU/h more than at present. Not quite enough but maybe with the other 2" duct going along the delta-T will improve a little more, and in any case it should be a substantial improvement.

I did try blocking off one of the galley hot air outlets and found that the reduced airflow led to the furnace outlet temperature climbing to an unacceptable degree. It would have tripped the limit switch had I left it blocked.
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Old 12-09-2010, 11:27 AM   #49
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I spent the night in the traylah last night and contemplated the problem.

My current thinking is that there should be enough room to run a separate 2" duct for the holding tanks from the furnace back thereby eliminating the need to T off the bedroom duct. This should result in a considerable improvement in heat delivery to the bedroom. It may also be possible to work in an additional 2" duct, again from the furnace back, open in the air space behind the shower. Warming up this area in that fashion would help keep the bathroom warm and would reduce the cooling effect on the bedroom duct.

The rated BTU/h output of the furnace is 26,000 BTU. The delta-T is around 100 degrees with the formula btu=1.08 * dt * cfm and some algebra the total airflow must be around 250 cfm. With four 4" outlets and one 2" outlet (with a quarter the airflow of the others) there's around 60 cfm per duct 4".

Because the delta-t is lower (45) at the bedroom outlet due to conductive losses, and because it only gets 80% of the airflow, due to the T for the tanks, it only gets around 2300 BTU/h (60 * 45 * .8 * 1.08). I think there's a heating shortfall of around 2500 BTU/h because if I put an electric heater back there on 750 watts things even out pretty well.

Adding the two 2" ducts should bring up the airflow somewhat and should also increase the delta T. I would expect it to come up to 65 degrees, which is what the bathroom area gets, (70+65 = 135, I measured 134), around 4200 BTU/h or 1900 BTU/h more than at present. Not quite enough but maybe with the other 2" duct going along the delta-T will improve a little more, and in any case it should be a substantial improvement.

I did try blocking off one of the galley hot air outlets and found that the reduced airflow led to the furnace outlet temperature climbing to an unacceptable degree. It would have tripped the limit switch had I left it blocked.
Nice analysis. So are you going to run that 2" duct up to the furnace for the tank area and remove the existing one? Let me know how you do it (pics). I think your layout is very similar to mine. This may be all that's needed...no additional fans.
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Old 12-09-2010, 11:51 AM   #50
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I'll try to get some pics. It's difficult because of the enclosed nature of the area but I'll do what I can.

I think I'll replace the 2" duct adapter now on the furnace with a 4" duct adapter, and use a couple of short sections of 4" duct and two 4x4x2 Ts and a 4x2 reducer to connect three 2" sections (the two existing ones going to the holding tank plus one going back past the shower). There is (barely) enough access to work on all this through the drawer opening under the sink, if the drawer is removed. The Ts will end up under the next cabinet section aft - there's 4" of dead space below the cabinet floor where the ducts run, and it's not crowded.
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Old 12-09-2010, 12:19 PM   #51
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ok I ordered the parts from this place.

https://secure.dhserver2.com/dwincorp_com/index.php

I'll post photos and updates. I'll be doing the install in the next few weeks so I can evaluate the results while the weather is cold enough to make the outcome obvious. If it works in January in Minnesota I can declare success.
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Old 12-09-2010, 12:58 PM   #52
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ok I ordered the parts from this place.

https://secure.dhserver2.com/dwincorp_com/index.php

I'll post photos and updates. I'll be doing the install in the next few weeks so I can evaluate the results while the weather is cold enough to make the outcome obvious. If it works in January in Minnesota I can declare success.
Great! I think you are set up differently. As I recall, (my trailer is in storage) I have two 4" runs, one to the bedroom and one to the bath. I recall only one 2" run, branching off the bath run, down into the tank compartments??????
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Old 12-09-2010, 01:16 PM   #53
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They gotta be the same...your curbside floorplan is identical to mine..unless some moder year change has taken place.
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Old 12-09-2010, 01:28 PM   #54
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It's easy to miss the forward 2" duct used by the factory. It comes right off the furnace and drops through a hole in the floor under the kitchen cabinets to the freshwater tank area.

I confirmed that the T branch on mine is in fact off the bedroom duct, though it's easy to imagine this varying from one trailer to the next due to, uh, manufacturing variances.
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Old 12-09-2010, 04:16 PM   #55
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Take a look at aheat.com these things are great
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Old 12-09-2010, 06:15 PM   #56
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It's easy to miss the forward 2" duct used by the factory. It comes right off the furnace and drops through a hole in the floor under the kitchen cabinets to the freshwater tank area.

I confirmed that the T branch on mine is in fact off the bedroom duct, though it's easy to imagine this varying from one trailer to the next due to, uh, manufacturing variances.
Really? Where do they enter the tank areas and how are they attached. I guess I kinda thought it (one) just hung down there where the pump pickup is and blew willy nilly into a cavity. Thanks for the heads up on a rodent entry point that I didn't know was there. How can I get to it? Behind the drawer under the sink?
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