Poorly designed ductwork - need opinions!

[Stefonius]

I have a fifth wheel with a heating problem. The duct feeding my bedroom is basically made of a sheet of 1/2" foam board taped across two aluminum floor joists. Both ends are capped off with foam board, and the space is fed by a flexible hose attached to the heater's distribution box. A neat idea, but kind of DUMB in its execution.

The foam board has warped and pulled away from the joists, so now there is no heat going to my bedroom and lots of heat going into the basement.

This makes DW very angry. Like, "Hulk Smash" kind of angry. We're going cold-weather camping next month, and I need to fix this before then or I'm a dead man. "D-E-D" Dead. She will stomp me flat and burn down the trailer if I let her freeze to death at night as if we were still tent camping.

What I'm planning to do is to get a rectangular to round 90 degree boot and attach it to the underside of the vent, then run galvanized round duct back to the flexible pipe from the furnace. I would then insulate the whole thing with some Roxul before putting foamboard back up across the joists.

I'd also like to replace the plain in-floor vent cover with one that allows me to partially close it (because it gets mighty darned hot in the bedroom if the ducting is working properly).

I am a jack of many trades, but HVAC isn't really one of them. Is this a good idea, or a bad one? Why? Other suggestions or helpful hints?

[Stefonius]

CJW8 wrote:
Sometimes our LR rug covers a vent and the furnace has never shutdown due to low flow or overheating. In-fact, you could use a small rug to partially cover your bedroom vent once you fix it. Put a string on both ends and give one end to the wife and keep one end for yourself. When you get hot, pull your string to cover the vent. When she gets cold, she can pull her string to uncover it. This facilitates the thermostat wars that all couples play!

I used to use a towel to cover half of the vent at night. I'm wondering if that is what caused the foam board & tape to sag and pull away from the joists in the first place.

[jodeb720]

My Cougar has the rectangular plenums under the floor from the heater distribution plenum. Since I've had it, it's never moved a lot of air. I eventually had to cut the seal and found that all the aluminum tape had torn along the seams and the hot air was leaking into the basement.

I converted all of it to 4" Diameter ducting and have never looked back.

It howls half the amount it used to

[CJW8]

Sometimes our LR rug covers a vent and the furnace has never shutdown due to low flow or overheating. In-fact, you could use a small rug to partially cover your bedroom vent once you fix it. Put a string on both ends and give one end to the wife and keep one end for yourself. When you get hot, pull your string to cover the vent. When she gets cold, she can pull her string to uncover it. This facilitates the thermostat wars that all couples play!

[Stefonius]

The furnace has several other outlets in the plenum which feed the bathroom, living/dining/kitchen and underbelly (for the tanks). Wouldn't restricting airflow to the bedroom simply cause more air to come out of the other outlets? I don't know enough about calculating airflow to know for sure.

[pianotuna]

Restricting the air flow may not be a good idea. It may cause the furnace to over heat, leaving cold air flowing to the bedroom.

[Hornnumb2]

You could use some home flex a/c duct if you have the space. It can be bought at Homedepot and such. It comes in 25ft in a box then you would have no seems to leak.

[imgoin4it]

If you install an adjustable grill or otherwise reduce the size of the existing duct and reduce airflow, make sure you don't reduce it enough that the furnace shuts down via the thermal cut off because the furnace got too hot.

[time2roll]

Perfect. Probably only need typical 4" tube but use the same as existing.
If you have access I would replace the entire tube and avoid the middle connection.

[Stefonius]

smkettner wrote:

Stefonius wrote:
the space is fed by a flexible hose attached to the heater's distribution box.

I would extend this flexible hose to the bedroom vent. May need a box at the end under the vent.

Something like this:

[Stefonius]

phillyg wrote:
Good idea but no need to use round galvanized; flex pipe will do it, and while you're under there I recommend you wrap aluminum sticky tape around every joint you can reach.

The existing flex pipe is too short to reach the duct (by many feet). I was just going to use a rigid pipe to bridge that gap. I'll definitely use aluminum tape on every seam I find.

Sooner or later I'm going to have to go through the entire trailer and fix the terrible job the factory did on all the heating runs.

I'm also wondering if the pipe feeding the bedroom vent is unnecessarily large. Maybe a smaller diameter pipe would lend the system a little more balance instead of roasting us in our sleep.

[time2roll]

Stefonius wrote:
the space is fed by a flexible hose attached to the heater's distribution box.

I would extend this flexible hose to the bedroom vent. May need a box at the end under the vent.

[downtheroad]

Stefonius wrote:
and I need to fix this before then or I'm a dead man. "D-E-D" Dead. She will stomp me flat and burn down the trailer if I let her freeze to death at night as if we were still tent camping.

Another plan would be to not fix it and let her, "burn down the trailer." Then you can buy a brand new one with good duct work....

[MEXICOWANDERER]

Was asked to do something similar in 2010 in Sta Rosa CA. I went to the hardware store bought a tall aerosol can of foam, and patched things up. Worked fine. Foam makes an intense glue bond. Hope this helps.

[phillyg]

Good idea but no need to use round galvanized; flex pipe will do it, and while you're under there I recommend you wrap aluminum sticky tape around every joint you can reach.