Not enough heat in back

[Jammer]

I decided to put the second register above the first in the existing carpeted box. It barely fits, and I don't especially like the way it looks, but cabinetry seemed like too big of an addition to an already major project.

I did some preliminary heat runs the other day when it was warmer and before I put the box back on and concluded that the directional registers do make a substantial difference. They were missing for the runs the other day and much of the hot air, I concluded, ended to up in the bathroom.

I also concluded that it is in fact necessary to block off one of the front registers completely to achieve balance.

Here are the results after five yours, with an outdoor temperature of 12 degrees:

Gaucho 68
Dinette 66
Head 73
Bed 68

Since I'm measuring the temperatures in the head on the lid of the head itself I'm finding that, now that there's enough airflow in the duct system, that measurement point isn't a good proxy for the air temperature in the room. (Recall that I'm using an infrared thermometer). The surrounding walls are not as warm.

Conclusions

I conclude that there is a flaw in the duct design leading to excessive hot air discharge in the front of the trailer and insufficient air discharge in the rear. Combined, this leads to the uneven heat originally observed.

High-quality insulation, carefully applied to the most likely sources of heat loss in the bedroom, made no measurable improvement in evenness of heat distribution.

By adding a 4" duct run to the bedroom, and removing one of the 4" registers facing the forward lounge area, it is possible to achieve reasonably even heat. It is necessary to rework the floor in the coat closet, reroute existing ducts, and trim and cut wall sections to do this as an aftermarket modification.

A more minor change, adding a 2" duct instead, was insufficient to address the problem.

[Jammer]

Addendum

I checked the trailer again after making the serpentine front duct modification described here.

Temperatures are close enough that I'm running into shortcomings in my measurement methodology and differences between one part of the room and another, and between furnace-running and furnace-resting conditions (that is, resting when the thermostat isn't calling for heat). In the bedroom, in particular, it is several degrees warmer in the middle of the streetside bed, where I've been taking my measurements, than on the curbside bed or especially the nightstand (due to its proximity to the large rear window).

The IR thermometer is also affected by differences in emissivity between materials, that is, the degree to which the surface being measured approximates a black-body radiator. While these differences are only a few degrees at this point in the experiment they're polluting the data.

I measured the temperature on the hickory doors and face frames, which should all have equal emissivity, and also walked through the trailer in only a T-shirt and pants to better feel the air temperature. I think at this point it is slightly warmer in the bedroom than in the lounge, although the difference is only 2-3 degrees. There is a slight cool spot near the dinette and the refrigerator, probably due to heat loss in the poorly insulated bulkhead wall between the dinette and the area where outdoor air circulates past the cooling unit for the fridge.

The major goal was to be able to maintain comfortable sleeping conditions throughout the trailer. I believe this goal is met at this point.

I'm going to leave the heat on overnight, in part to force outgassing of the new ducts, and also so I can confirm results in the morning after a longer period for temperatures to equalize. They're forecasting a low around 10 degrees tonight.

[ROBERTSUNRUS]

Hi, it seems that my un-scientific ideas worked.

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.

Originally Posted by 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.

Originally Posted by 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]

Originally Posted by dznf0g

I don't know why that wouldn't be OK.

Originally Posted by Jammer

As noted upthread, there isn't room for another 4" duct under the coat closet or behind the shower.

Originally Posted by ROBERTSUNRUS

Hi, how did you finally remove the carpeted box? I believe you said earlier that it was stapled in place; I have removed my carpeted box and found it was held in place by four screws that were driven into the carpet and very hard to find. I may in the future build another box out of oak instead of carpet over plywood. If you are able to run two 4" ducts to the bedroom and eliminate one of the front ones, you could fill the hole with something similar to the porch light and use it for an entrance light.

Originally Posted by Jammer

The carpeted box is fastened exactly as you said. I had looked in the 4" hole and saw staples but those just attach the 1x1 "nailer" piece to the bulkhead and the bed cabinetry. The carpeted box had four screws holding it in place. One of them missed the "nailer" so I only had to remove three.

I've been thinking about what to do in front. It won't be clear until I have everything reassembled and some colder weather to retest the balance whether both front registers will stay or not. I'd like to remove one and then loop the duct around a little for the other one to help with the blower noise. I removed my magazine rack to make room for a larger fire extinguisher and might end up reinstalling it over the old register hole, though the porch light idea is intriguing.

Originally Posted by Jammer

I decided to put the second register above the first in the existing carpeted box. It barely fits, and I don't especially like the way it looks, but cabinetry seemed like too big of an addition to an already major project.

I did some preliminary heat runs the other day when it was warmer and before I put the box back on and concluded that the directional registers do make a substantial difference. They were missing for the runs the other day and much of the hot air, I concluded, ended to up in the bathroom.

I also concluded that it is in fact necessary to block off one of the front registers completely to achieve balance.

Here are the results after five yours, with an outdoor temperature of 12 degrees:

Gaucho 68
Dinette 66
Head 73
Bed 68

Since I'm measuring the temperatures in the head on the lid of the head itself I'm finding that, now that there's enough airflow in the duct system, that measurement point isn't a good proxy for the air temperature in the room. (Recall that I'm using an infrared thermometer). The surrounding walls are not as warm.

Conclusions

I conclude that there is a flaw in the duct design leading to excessive hot air discharge in the front of the trailer and insufficient air discharge in the rear. Combined, this leads to the uneven heat originally observed.

High-quality insulation, carefully applied to the most likely sources of heat loss in the bedroom, made no measurable improvement in evenness of heat distribution.

By adding a 4" duct run to the bedroom, and removing one of the 4" registers facing the forward lounge area, it is possible to achieve reasonably even heat. It is necessary to rework the floor in the coat closet, reroute existing ducts, and trim and cut wall sections to do this as an aftermarket modification.

A more minor change, adding a 2" duct instead, was insufficient to address the problem.

[handyman1425]

I seen in my 85 31' side bath they had a optional zone heat that had a second heater were did they put that?

[dznf0g]

Originally Posted by Jammer

I decided to put the second register above the first in the existing carpeted box. It barely fits, and I don't especially like the way it looks, but cabinetry seemed like too big of an addition to an already major project.

I did some preliminary heat runs the other day when it was warmer and before I put the box back on and concluded that the directional registers do make a substantial difference. They were missing for the runs the other day and much of the hot air, I concluded, ended to up in the bathroom.

I also concluded that it is in fact necessary to block off one of the front registers completely to achieve balance.

Here are the results after five yours, with an outdoor temperature of 12 degrees:

Gaucho 68
Dinette 66
Head 73
Bed 68

Since I'm measuring the temperatures in the head on the lid of the head itself I'm finding that, now that there's enough airflow in the duct system, that measurement point isn't a good proxy for the air temperature in the room. (Recall that I'm using an infrared thermometer). The surrounding walls are not as warm.

Conclusions

I conclude that there is a flaw in the duct design leading to excessive hot air discharge in the front of the trailer and insufficient air discharge in the rear. Combined, this leads to the uneven heat originally observed.

High-quality insulation, carefully applied to the most likely sources of heat loss in the bedroom, made no measurable improvement in evenness of heat distribution.

By adding a 4" duct run to the bedroom, and removing one of the 4" registers facing the forward lounge area, it is possible to achieve reasonably even heat. It is necessary to rework the floor in the coat closet, reroute existing ducts, and trim and cut wall sections to do this as an aftermarket modification.

A more minor change, adding a 2" duct instead, was insufficient to address the problem.

Jammer,

Let me make sure I understand you last analysis. If I run a new 4" duct to the BR, utilizing a new collar at the air box, remove one of the registers from the LR and install it in the BR, then install a register with a shutter in the LR, that will give me the flexibility to regulate front to back heat as I wish?

What did you find out on that last 10 degree night?

Thanks for all your work on this, very helpful.

[Jim Foster]

After reading what others have done with little or no success, I ordered a Rule 4" bilge blower which should get here in a week or so. I will install it in the hose going to the bath at a point just before the register.

I will post back after the installation to let you all know how it works out.

[Jammer]

Originally Posted by dznf0g

Jammer,

Let me make sure I understand you last analysis. If I run a new 4" duct to the BR, utilizing a new collar at the air box, remove one of the registers from the LR and install it in the BR, then install a register with a shutter in the LR, that will give me the flexibility to regulate front to back heat as I wish?

Yes, although you may be just as well served by blocking the front duct off completely. An advantage of doing this is that you can reuse the collar so you don't have to buy one.

What did you find out on that last 10 degree night?

I checked temperatures the following morning and found that nothing much had changed since the night before. It was slightly warmer in the bedroom, 2-3 degrees, than in the lounge; and slightly cooler at the dinette than in the lounge.

The variation in temperature at different measurement points within each area was greater than the 2-3 degree average difference between front and rear. For example, there was a difference of 3-4 degrees between the streetside and curbside bed, and a 4-5 degree difference between the heads of the beds and the feet of the beds, differences between the streetside end, center, and curbside end of the gaucho, and so on. Subjectively, walking through the trailer, it was slightly cooler in the galley/dinette area than the ends, slightly warmer in the lavatory, and there was no perceptible difference between the lounge and bedroom areas.

The winter outdoor temperatures exaggerate the differences. In more typical camping weather I expect any unevenness to be imperceptible.

[dznf0g]

Originally Posted by Jammer

Yes, although you may be just as well served by blocking the front duct off completely. An advantage of doing this is that you can reuse the collar so you don't have to buy one.

My thought for having the damper equipped register in the LR is:

During the day, open the LR register for warmer in the living area.

At night, close off the LR register and route more heat to the BR.

[Jim Foster]

Originally Posted by Jim Foster

I will post back after the installation to let you all know how it works out.

My new Rule bilge blower came yesterday. After lunch today I made a trip to the auto parts store for some wire. connectors and a fuse holder. I started on the job about 3:30 and finished about 4:30. I mounted the blower just ahead of the register in the rear bath. The blower switch. which turns blue when on, is mounted just above the water heater switch which glows red when first turned on.

With the furnace on, I turned on the blower. Oh baby, it blew the bathroom full of nice warm air in about two minutes, and that was with the sliding doors to the bathroom open.

We are headed out on a road trip on the 19th, which may last 6-7 weeks. We'll now find out if the warm air is a problem for the blower. I'll post back on this thread upon our return, or sooner if there is a problem.

Oh, the total cost came to $43.13, but I have some wire and connectors left over for another job.

[dznf0g]

Originally Posted by Jim Foster

My new Rule bilge blower came yesterday. After lunch today I made a trip to the auto parts store for some wire. connectors and a fuse holder. I started on the job about 3:30 and finished about 4:30. I mounted the blower just ahead of the register in the rear bath. The blower switch. which turns blue when on, is mounted just above the water heater switch which glows red when first turned on.

With the furnace on, I turned on the blower. Oh baby, it blew the bathroom full of nice warm air in about two minutes, and that was with the sliding doors to the bathroom open.

We are headed out on a road trip on the 19th, which may last 6-7 weeks. We'll now find out if the warm air is a problem for the blower. I'll post back on this thread upon our return, or sooner if there is a problem.

Oh, the total cost came to $43.13, but I have some wire and connectors left over for another job.

Thanks, Jim.

Can you take some "room" temps on your trip and let us know if you have even heating throughout the unit?

[Jammer]

How does the noise level compare to the noise made by the furnace itself?

[StreamNTyme]

hi there,

that is a lot of work to go through...wow
we got a nice, very comfy and cozy electric blanket from my daughter for Christmas, wow...

it is wonderful to snuggle into a nice warm bed in this horrible weather we are presently having on the east coast....

ahhh simple pleasures...

[Jammer]

Choices, choices.

Electric blanket as a practical matter requires shore power. There are 12v ones out there or you could run an inverter, but the batteries won't last long.

In my case there was a fair amount of extra work from the experimenting and false starts trying to find the MINIMUM set of modifications that would provide an EFFECTIVE solution. Others can learn from this too.

Also, not only does it get colder in my part of the country than South Carolina, but the summer is considerably shorter, and many trips end up being taken in spring and fall.

Lots of work... yes... worth it?... we'll see, BUT bear in mind that even with no wind the bedroom and bathroom are too cold to be comfortable with the stock heat and cold outside temps. So you can make it a CAMPING trip...

... or abandon the rear half of the trailer and live next to the furnace.

... then again ... if that's all the room I thought I needed, I'd have a GLOBEtrotter.

[Jim Foster]

Originally Posted by dznf0g

Thanks, Jim.

Can you take some "room" temps on your trip and let us know if you have even heating throughout the unit?

The heating will not be close to even throughout. I am not looking for that result. When it is shower time, we will turn the blower on and heat the bath room. Off when finished, so that the majority of the heat goes to the living room area as it does now.

[Jim Foster]

Originally Posted by Jammer

How does the noise level compare to the noise made by the furnace itself?

The blower noise is higher than the furnace. It is not something you would want to have running all of the time, but that is not what I was looking for. Only looking for heat in the rear bath when wanted.

Like I said, this thing really moves the air. It will only take a minute or two to heat up the bath, as it will already be somewhat warm, just not toasty.

Just a real nice boost.

The blower draws 4 amps.

[Jim Foster]

Just had another thought. I should probably stop thinking.

If someone wanted to get a little fancy, the bilge blower could be wired through a control device, perhaps an after market variable speed windshield wiper switch like we use in street rods, to slow the blower way down so that it could be used to adjust the air going to the back of the trailer, Then you could really keep the trailer at a constant temperature throughout. Then crank it up at bath time.

[dznf0g]

Originally Posted by Jim Foster

Just had another thought. I should probably stop thinking.

If someone wanted to get a little fancy, the bilge blower could be wired through a control device, perhaps an after market variable speed windshield wiper switch like we use in street rods, to slow the blower way down so that it could be used to adjust the air going to the back of the trailer, Then you could really keep the trailer at a constant temperature throughout. Then crank it up at bath time.

I have just designed (on paper) and procured parts to perform this function with a parallel circuit for the furnace blower. Not to even out heat, but to supplement the propane heat with electric and still keep enough warm airflow to the tank compartments. My fear is, with electric supplement, that the furnace will not run enough to keep the tanks from freezing. So I want to keep a small volume of air flowing to the tanks at all times while on shore power and electric heat.

I am using a heater blower switch and resistor block for an 86 Chev van (use what you want, this is just an older, very simple circuit design) and wiring to use low and medium #1 speeds only. When I get around to actually installing the circuit, I'll post pics and performance.

[Jammer]

The automotive blower resistor blocks do have to be in moving air or they will overheat.

There are a variety of dropping resistors out there that have a more flexible thermal design. Also, you might consider a PWM circuit, which would have the advantage of lower power draw.

[dznf0g]

Originally Posted by Jammer

The automotive blower resistor blocks do have to be in moving air or they will overheat.

There are a variety of dropping resistors out there that have a more flexible thermal design. Also, you might consider a PWM circuit, which would have the advantage of lower power draw.

Yeah, I actually have some dropping resistors in varying resistance values out in the garage. If I wind up using the automotive resistor block, I plan on cutting a hole in the furnace blower box just like in the automotive application. When I get the experiment going I'll try several setups. I'm not really concerned about the power draw issue as this circuit will only be used while on shore power to move electrically produced heat around. When off the grid the normal propane furnace on time will keep the tanks protected.

[Jammer]

How much electric heat do you have and where? I have 3000 watts and when temperatures are below freezing outside the propane still runs a great deal.