Not enough heat in back

[Jim Foster]

Originally Posted by dznf0g

I'm not sure if the heat will hurt the bilge blower, or computer fan like in another post, but let us know how it works out.

I really don't think heat will be an issue. We boated in the Sacramento Delta for thirty years. The engine compartment on a run-a bout boat can get very warm sitting in the sun in the summer.

If I do this, we'll all find out. I will certainly post my findings. Won't happen until after the first of the year, as we will be on the road until then. I really don't like to get into projects, even small ones, on the road if I can help it. It always seems that the one tool that will make the job easier has not made the trip.

[Whirlaway]

After spending the weekend on my side, back and belly trying to figure out this heating, I am more confused now. There seems no reasoning why the heat blasts the living space then there's no or little heat in the fb and bath.

I have a little more than a ten (10) degree difference between the two (2) areas. Nothing new everyone is reporting these numbers. However the FB has the thermostat and it's calling for heat and not getting it. Can we trick the thermostat somehow?

When the heat is running it's roaring in the galley area.

Lin.

[Jammer]

OK gang another night for carving up a perfectly good new trailer. You folks with the 1975 Sovereigns who are wishing you had just bought a new traylah that didn't need any work... it's not like that...


The supplies showed up quickly from DWI and one other source. Pictured are the two sizes of duct, a 4x4x2 tee, a 4" Atwood duct adapter, and a 4x2 reducer. The Atwood duct adapter had to be ordered from another place because DWI doesn't sell them. In the end I did not need use the T. In addition to these materials I needed a 4" stainless steel clamp and a 2" stainless steel clamp, and a couple of sheet metal screws.

Tools required were a 2 5/8" hole saw, cordless drill, drill bits, a hammer and punch, and screwdrivers.

[Jammer]

It turned out there wasn't enough clearance for two Ts so I ended up moving the 2" outlet on the furnace to the next position forward. This required punching out the knockout with a hammer and drift, fiddly to do with the furnace installed, but possible with perseverance. The 2" outlet was moved to this opening and the new 4" outlet installed in the aftward one from which the 2" outlet had been removed.

The outlets attach using a clever sort of bayonet arrangement but the mother ship put in a couple of screws in each one, too, just to be sure. In true mother ship fashion one of them didn't actually hit the furnace and so served no purpose. Start using a jig and predrilling them before assembly in a more controlled environment, guys. But I digress.

I followed the mother ship's lead and used a screw in each one in addition to the retention provided by the bayonet.

The completed shot does not show a 4" clamp because I was one short in my planning. Some other day.

The existing 2" duct that disappears into the floor is then reattached to the front outlet, and a new piece of 4" duct is attached and run aftward.

[Jammer]

Moving aftward the next shots show the T and reducer installed under the drawers under the microwave. First I assembled the T and reducer using sheet metal screws. They fit snugly so no tape or sealant is required. Then the new 4" duct from the furnace is cut to fit the large end of the T, and two pieces of 2" duct are attached to the outlets. The whole thing fits under the drawers.

[Jammer]

The two new 2" ducts proceed under the range, where I couldn't get a photo, and then emerge under the false floor in the coat closet. I had to use the hole saw to drill a hole for one of them because there is some excess internal wall that blocks access.

These next shots are looking down into the coat closet. In the bottom of the photo (toward the center of the trailer) you can see the wall box for the pic-a-watt heater I installed previously. I removed the existing 4x4x2 T and the short section of 2" duct that went down to the fresh water tank. I was able to splice the two existing pieces of 4" ductwork together by hand and will run some tape over them at some point. This is what the mother ship does (see downthread). The other piece of 2" duct continues to the shower area aft of the closet.

The changes leave this area no more or less cluttered than before, since the T is gone, but there's one more duct.

[Jammer]

My original plan had been to run one of the 2" ducts to the carpeted box at the head of the curbside bed (I have a twin) where the existing 4" duct emerges in a register.

It turns out that the way Airstream builds these, the bulkhead between the shower and the bedroom is the same for twins and queens, so there's only a 4" hole. Airstream spliced a couple feet onto the duct using clear packing tape. Jackson Center, meet duct tape; despite widespread misuse it is in fact the proper product for joining ductwork.

Anyway, the only access into this area is through the 4" hole at the front of the carpeted box, and the box is assembled and attached to the underbed cabinetry and the bulkhead using staples. Experience has shown that it is nearly impossible to disassemble stuff like this without damaging it.

I've decided to just let the 2" duct terminate behind the shower, for now. At some point I may try to get a right angle drill and a hole saw inside the duct outlet but that's going to be a time-consuming ship-in-a-bottle type of project and great care will be required to be sure the hole doesn't end up going through the fiberglass shower stall or some other equally critical component.

[Jammer]

Here's a shot of the bottom of the closet with the ducts removed. It's hard to see what's what but the short of it is that the loose duct that terminates in this area is warming one end of the fresh water tank. You can see the tank sensor near the center of the photo, and the PEX tank outlet that goes to the water pump at left center. I don't know whether the sheet metal at the top of the photo is double wall or is the same piece that you can see under the trailer from the outside. I believe the vertical line to the right is one of the low point drains.

[Jammer]

I blocked off half of one of the front heat outlets temporarily with some foam to take measurements. I have some 1/4" flame retardant foam sheeting on order. When it arrives I'm going to wrap into a cylindrical shape and put inside the very short section of ducts coming forward from the furnace, both for noise control and to reduce the airflow by an equivalent amount.

I'll copy my earlier observations from upthread, and add the difference between the gaucho and the other locations in brackets.

Originally Posted by Jammer

In 15 degree outside temps, running the furnace (only, not any of my electric heat), I recorded these temperatures:

Gaucho 69
Dinette 66 [-3]
Head 61 [-8]
Bed 58 [-11]

Tonight it is a little cooler, around 11 degrees. The measurements now:

Gaucho 68
Dinette 66 [-2]
Head 65 [-3]
Bed 59 [-9]

The cold weather makes this a somewhat more demanding test, and I estimate a 5% reduction in the bracketed values if I were to retest in 15 degree conditions.

I'm pleased with the improvement in the head. The temperature measured at the bed, while better, is still a disappointment.

[Jammer]

Looking at the duct temperatures, upthread we had:

Originally Posted by Jammer

Galley outlets - 160 degrees
Head - 134 degrees
Bedroom - 104 degrees

With the front outlet half blocked off as shown above I measured these values after the modifications:

Galley outlets - 162
Head - 137
Bedroom - 112

I'm not sure where to go from here. While the logical next step would be to insulate the ducts, clearance is tight.

[Westfalia]

Have you considered using some reflectix wrap for some of the straight runs of ducting? its not high r value but is better than what is there now and is thin enough to work with in tight spaces. I also ended up wrapping some of the enclosed compartments in reflectix on exterior surfaces to slow the heat transfer.

[Jammer]

That's the sort of thing I'll have to consider. I'm going to have to measure and figure out how much clearance there really is to work with. Part of the problem is that, to insulate enough of the run, the range will have to come out, which will be a bigger project than what I've done so far.

Another possibility might be to better insulate the exterior compartment doors. The twin layout has three large externally accessible storage lockers. The queen only has one. It's one of the advantage of the twin layout. But perhaps that contributes to the heat loss.

[Dave Park]

You can also apply a layer of reflectix or similar to the inside walls of the cabinets, especially around that run. That will raise the ambient temperature in those spaces a bit, and as we were taught in school, heat likes to travel down a gradient and does so faster on a steeper gradient. It will also help with condensation (or move it somewhere better ventilated.)

[Westfalia]

Dave , that is exactly what I had done. While I have no quantative data on temperature increases, i do feel that this has helped duct temp to the front bedroom and reduced drafts.

[Aage]

It's a pity that AS decided to go with that plastic over spring "cheap dryer vent" design of supply tube for the hot air.

The added resistance due to the turbulence the grooves create costs you a lot of air pressure on long runs, plus encourages dust to collect fast, as anyone with one of those tubes on their dryer already knows.

As I previously stated, on mine they still used a mini version of what tin-whackers still put in new homes (steel). And just re-sealing the joints with duct tape improved the heat and airflow on the long runs (like to the bathroom in the rear) on my '74 Sov.

Question: in the photo showing two vents (one is half plugged), are they both hot air supply vents?

[Jammer]

The two vents are both hot air supplies. They are within inches of the furnace and emit a good deal of heat and noise.

[ROBERTSUNRUS]

Originally Posted by Jammer

The two vents are both hot air supplies. They are within inches of the furnace and emit a good deal of heat and noise.

Hi, your trailer and your furnace are larger than mine, but my furnace only has three vents. One in the bedroom, one in the bathroom, and one in the livingroom. The one in the livingroom is located under my oven, by my entrance door, and only inches away from the actual furnace; Could you block one of the close ones off so you can get better circulation on the other ones? With two vents that close to the furnace, I can't believe that there would be much pressure or heat left for the vents 15' to 20' away.

[dznf0g]

Originally Posted by ROBERTSUNRUS

Hi, your trailer and your furnace are larger than mine, but my furnace only has three vents. One in the bedroom, one in the bathroom, and one in the livingroom. The one in the livingroom is located under my oven, by my entrance door, and only inches away from the actual furnace; Could you block one of the close ones off so you can get better circulation on the other ones? With two vents that close to the furnace, I can't believe that there would be much pressure or heat left for the vents 15' to 20' away.

Robert,

I'll bet, if you look in your furnace installation materials, it will say that a minimum of three 4" ducts are required for proper airflow volume and heat removal from furnace box. I know the larger furnace in mine requires four 4" exits. Blocking off one of the vents may raise the furnace plenum temperature to a level unacceptable from a durability and safety standpoint.

[Jammer]

Robert,

It has been suggested. The Atwood installation guide for this furnace says that a minimum of four, 4" diameter ducts leading to nonadjustable (that is, always fully open) registers are required. Blocking off one of the front outlets, completely, would leave only three 4" diameter ducts plus the three 2" outlets, somewhat less than the total area Atwood says is required. In measuring the outlet temperature, it's 170 degrees once the trailer is warm. The high limit trip point for the furnace is 190 so there's not much blocking off of the outlets that I can do without getting close to the trip point.

The furnace is more or less in the center of the trailer and so the idea of having two forward vents and two aft vents makes sense except for the fact, as you point out, that the two forward vents emit far more heat due to their proximity to the furnace.

[ROBERTSUNRUS]

Hi, then what if we block off one of the front vents and run a new one to the bedroom instead? [two in the bedroom and one in the living room]