Cold Air Intake

sandpirate · Jan 2, 2011

I recently discovered that my furnace was returning air from the underbelly of my coach along with the air inside my coach (not a good thing when you are trying to keep the coach warm). I discovered the problem when I was searching for my water pump that quit performing on our recent trip. Due to a number of floor penatrations needed under and near the sink area a large portion of the floor had been cut out to make it easier to route the piping and wiring during construction. Unfortunately this is also return air space for the furnace and will require some floor sealing, insulation, and some time to clean up the rats nest of wiring and piping that plague this small access area.

You may want to check your coaches for similar areas...

TandT · Jan 2, 2011

Which coach do you have? Thanks.

hoefler · Jan 3, 2011

In order to heat the basement and the tanks in the under belly, you have to have return air to the furnace. If you blow air into a sealed area or an area that may vent to the outside, you have to have a return of some sort for make up air. If it did not pull air from the under belly, it will have to pull it from some place else. The furnace needs to pull air from the under belly for proper circulation and to heat the tanks and plumbing, if it didn't, your chances of freezing up are greatly increased.

sandpirate · Jan 3, 2011

TANDT said:
Which coach do you have? Thanks.

Cyclone 2812

sandpirate · Jan 3, 2011

hoefler said:
In order to heat the basement and the tanks in the under belly, you have to have return air to the furnace. If you blow air into a sealed area or an area that may vent to the outside, you have to have a return of some sort for make up air. If it did not pull air from the under belly, it will have to pull it from some place else. The furnace needs to pull air from the under belly for proper circulation and to heat the tanks and plumbing, if it didn't, your chances of freezing up are greatly increased.

The return air is air that is supposed to be coming from the conditioned space to be heated, not from the outside(there are plenty of vents in the trailer for fresh air intakes). Furnace supply air is heated air that is to feed the coditioned space and keep it warm. If it was the intention of the manufacturer to heat the underbelly then there would be supply air feeding the area below the trailer, not return air. The reason for the air exchange in my trailer is poor workmanship and lack of quality control.

hoefler · Jan 3, 2011

The underbelly and the basement are considered conditioned areas if you are going to heat them.

westxsrt10 · Jan 4, 2011

hoefler said:
In order to heat the basement and the tanks in the under belly, you have to have return air to the furnace. If you blow air into a sealed area or an area that may vent to the outside, you have to have a return of some sort for make up air. If it did not pull air from the under belly, it will have to pull it from some place else. The furnace needs to pull air from the under belly for proper circulation and to heat the tanks and plumbing, if it didn't, your chances of freezing up are greatly increased.

The basement is not a 'condition space', no air movement at all is wanted. Pulling fresh air from the underbelly will only make everything colder. The underbelly tanks are heated by the ductwork making contact near and around the holding tanks.

porthole · Jan 4, 2011

The cyclone underbelly is "heated" by a plenum discharge into the underbelly - 4" hole I think.

There is no heat conduction between tanks and duct work.

jpajax · Jan 4, 2011

My 3410 BH is the same way. I would rather pressurize the basement rather than pull cold air in from the outside. don't know if this was the plain or it was over look in construction.

grizzlygiant · Jan 4, 2011

There are so many gaps in the underfloor covering that pressurizing the basement is impossible. Pulling return air from the basement would suck in cold external air resulting in a COLDER basement as well as inefficient heating of the coach interior. The return air should be ONLy from the coach interior; plug/seal all the "sloppy workmanship" holes in the subfloor.

sandpirate · Jan 4, 2011

grizzlygiant said:
There are so many gaps in the underfloor covering that pressurizing the basement is impossible. Pulling return air from the basement would suck in cold external air resulting in a COLDER basement as well as inefficient heating of the coach interior. The return air should be ONLy from the coach interior; plug/seal all the "sloppy workmanship" holes in the subfloor.

I spent the better part of the evening cutting styrofoam sheets up to cover the holes leading to the belly of the carriage to keep my furnace from sucking the air from down there and outside.

I originally thought that the sheeting under the coach might be pretty well sealed; until I crawled under the trailer because of a water leak caused by loose freshwater hose clamps...After working under there for a few hours I realized that it will probably take me several hours and at least 2 rolls of aluminum tape to seal up all of the cut outs and open areas around the perimeter of the underbelly sheeting. After getting a real good look under the hood I can't say that I can give any props to the manufacturer.

sandpirate · Jan 4, 2011

porthole said:
The cyclone underbelly is "heated" by a plenum discharge into the underbelly - 4" hole I think.

There is no heat conduction between tanks and duct work.

I have followed all of the supply lines from the furnace and have not seen any that dump into the belly of the coach. To check that out I will close off most of the interior furnace supply vents and turn on the furnace and climb under the trailer and put my hand by one of the many openings in the underbelly sheeting and feel for any heat or air movement coming from inside.

DW_Gray · Jan 4, 2011

Yep, I have the same problem. I learned that last winter in the extreme cold (for a Cyclone). I estimate about half of the fresh water tank froze up and the lines would freeze just about every night. I have since used some insulating foam sealant from Home Depot to seal most of the small gaps. I still have a little more work to do like closing up that big hole near the furnace. I can actually feel a breeze of cold air come out through what suppose to be the return vent in front of the furnace. Fortunately I'm not in a freezing area now.

hoefler · Jan 5, 2011

In our Landmark, there is a 2" flex hose from the furnace running through the basement and ends under the black tank and above the front gray tank and blowing toward the rear tanks. I can open the basement door to the compartment under the shower and access to the back of the water heat, the UDC, battery box, converter, etc.. I can see straight through to the furnace, there is no attempt to close it off from the living area. Any area that you want to control the temperature in, whether you heat or cool it, it is a conditioned area. I still contend, if you are going to heat the basement/under belly area, if you discharge hot air in this area, you will need a return. If you just blow air out side of the living area, you will have to have make up air from somewhere, otherwise you would have a vacuum.

jpajax · Jan 5, 2011

If you have a return duct from the camper living area to the furnace were it does not draw any air from the basement. That is what I call pressurizing the the basement it will force air out the holes not draw air in. But I have been known to be wrong about my off the wall theory's.

DW_Gray · Jan 6, 2011

Here is a picture example. Like I said above, I haven't closed all the holes up below the underbelly as well as the big cutout between the furnace and the underbelly like SandPirate is talking about.

As you can see in the picture, there is a significant amount of airflow coming from outside and the underbelly into the coach. This is not normal. I've never lived in any house that the furnace return had outside air connected with the heating system. The return air should only recirculate from inside the coach through the furnace and back out the ducts as heated air.

As for return air for the underbelly, I don’t think that is an issue to consider when there isn’t any insulation down there. But stopping cold outside air from coming into the coach is.

hoefler · Jan 6, 2011

jpajax said:
If you have a return duct from the camper living area to the furnace were it does not draw any air from the basement. That is what I call pressurizing the the basement it will force air out the holes not draw air in. But I have been known to be wrong about my off the wall theory's.

OK, when you pressurize that area and air is leaking to the out side, where do you get air to make up what you have blown out side?? It has to come from somewhere. Lets say your living area is air tight, you would create a vacuum in the living area, once the furnace shuts down, you would suck cold air in any hole you would leak air out of until your inside would equalize with the outside. Once you build up the pressure in an area and equals the output of the source of the pressure, you will not get any more air in there than what leaks out any holes. You will have the area pressurized before you get any heat since the blower will start circulating air before it gets warm. Your output of the blower is greater than any leak you may have or not, you would get very little warm air in that area before the thermostat in the living area is satisfied and shuts down the furnace.

Riverman · Jan 6, 2011

I checked for furnace supply lines while I had the underbelly removed from our Cyclone.
I was more concerned with the furnaces inability to heat the inside of the trailer than I was with the underbelly.
What I found was a couple 3" holes cut into the main ductwork near the fresh water tanks.
I covered them over with duct tape. This made the inside of the trailer a bit better in near freezing conditions.
We would rather have frozen tanks than feet.
Seems this furnace has a hard time keeping one area from freezing - much less 2.
The effort into the underbelly is futile without any insulation down there.

hoefler · Jan 6, 2011

Riverman said:
I checked for furnace supply lines while I had the underbelly removed from our Cyclone.
I was more concerned with the furnaces inability to heat the inside of the trailer than I was with the underbelly.
What I found was a couple 3" holes cut into the main ductwork near the fresh water tanks.
I covered them over with duct tape. This made the inside of the trailer a bit better in near freezing conditions.
We would rather have frozen tanks than feet.
Seems this furnace has a hard time keeping one area from freezing - much less 2.
The effort into the underbelly is futile without any insulation down there.

Very true!

DW_Gray · Jan 6, 2011

I closed up the big hole (cut out) between the furnace and basement equipment compartment today. I used a roll of home hot water heater insulation I retrieved storage. That stopped the cold air draft and I can already feel the difference. My feet aren't cold now and the floor level thermometer in the my electric heater has increased 5 degrees.

So if you haven't fixed your RV yet, then what are you waiting on?

"Git R Done"

Cold Air Intake

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