Pulling new heater duct

[Missionstreet]

Looking into replacing my old smelly heater 4" duct pipe.

Is semi rigid metal pipe acceptable substitute? The only other selection I found at the "box" store was some spiral wound "foil" pipe that feels weaker that the original existing.

Also, the sections running to the bedroom and bathroom I was thinking of pulling the new in with the old. Is this a good idea?

My concern is what looks like the existence of nails under the floor that might puncture the pipe as it is being pulled.

I believe it was all open when originally assembled on the "jig."

[ktmrfs]

Missionstreet wrote:
Looking into replacing my old smelly heater 4" duct pipe.

Is semi rigid metal pipe acceptable substitute? The only other selection I found at the "box" store was some spiral wound "foil" pipe that feels weaker that the original existing.

Also, the sections running to the bedroom and bathroom I was thinking of pulling the new in with the old. Is this a good idea?

My concern is what looks like the existence of nails under the floor that might puncture the pipe as it is being pulled.

I believe it was all open when originally assembled on the "jig."

One of the first things I did when we got our outback in 2011 was to drop the underbelly cover and replace ALL the ducts with ridgid ducts. The spiral wound stuff has lots of resistance to airflow and then wrap it with the thin adhesive backed foam/foil insulation. Airflow went up, and air was warmer coming out of the ducts.

[Missionstreet]

Thank you all this is very informative and inspiring

[jodeb720]

In my 5er, the plenums in teh floor were leaking from the get go. it would take 20 minutes for a 5 degree rise.

After doing some solid research and verifying it with some folks here, I bypassed the original plenum, used insulated ducting like shown in Mike's picture and now it works sooooo much better. I did have to so some imagineering to get the new ducts through the and around the cabinets, but in the end, i'm much happier.

As they say, it's not easy - but when it's done correctly, it works so much better.

[Vintage465]

There is a lot of good thinking behind using an actual elbow to get around a corner if it possible to do that. Problem is usually where it's that tight, it'd be stinker to try and get a elbow in there. I'm in the "mental engineering" phase of adding some ducts to cabinets so the coffee cups aren't ice cold on those 20-30 degree mornings. I also need to add a duct over to my wifes side of the dinette so she's not freezing her legs off while I roasting on my side of the dinette.

[Microlite_Mike]

Missionstreet wrote:
Looking into replacing my old smelly heater 4" duct pipe.

Is semi rigid metal pipe acceptable substitute? The only other selection I found at the "box" store was some spiral wound "foil" pipe that feels weaker that the original existing.

Also, the sections running to the bedroom and bathroom I was thinking of pulling the new in with the old. Is this a good idea?

My concern is what looks like the existence of nails under the floor that might puncture the pipe as it is being pulled.

I believe it was all open when originally assembled on the "jig."

The ducting used in most RV's is usually flimsy and inefficient. I had to replace all mine from furnace to registers which wasn't as monumental in my TT as it could be in others.

I used a better grade of ducting that doesn't kink as easy as the factory type which seems to be just aluminum foil over a slinky.

If I were to do it again I'd use some insulated ducting like this:



With my new ducting I get more flow from the registers but a lot of heat is dissipated in areas I don't necessarily want more heat (like around the power distribution center/converter and under refrigerator) so insulation will direct more heat out into the living space.

This insulated 4" ducting is available at Lowes with a 25' piece selling for ~$40. Where the duct has to make sharp bends I'd add a metal fitting to make the bend and then just wrap it with fiberglass strip insulation and cover with Duct Tape. A little more effort and modest expense but far more efficient and easier on furnace.

As for heat in cabinet/storage areas to prevent water line freezing in cold weather, just add some ventilation louvers to the closed off areas that will both allow living area heat to travel into these spaces and also provide year-round ventilation that mitigates moisture damage.

Semi-rigid metal ducting will work but will radiate far more heat in spaces you don't necessarily want and less in areas where you do.

[Cummins12V98]

Look to see if you have a Gensco in your area or another HVAC Supply House. They will have heat rated Grey flex duct in your size. Make sure to tell them you need the heat rated as it's on the supply side of the furnace.

Visually it is grey in color and has a rubbery feel to it. This did it's job and did not melt or ignite.

[midnightsadie]

O zone your duct work.

[nickthehunter]

YOMV - but pushing any type of cleaning tool into your ducts would be a bad idea.

[CA_Traveler]

X2 They can be cleaned with compressed air and a snake.

[BobsYourUncle]

Replacing ducts would be a tall task. They are all joined together, there are corners and jogs etc. Existing ones likely have some kind of duct / foil tape sealing them. They will be attached to the floor in various places.

Ducts are all installed while the unit is being built, prior to assembly of floor sheeting and more.

Anything can be done, but you'd have to open up the floor to access them. "Pulling" the ducts is not an option.

IMO, the best option would be to clean the existing ducts. Get in there with some kind of flexible snake with a cloth on the end, wet with a cleaner.
You could even remove the furnace, take it apart and thoroughly clean everything.

Spiral round flexible pipe is a great dirt trap. They are full of ridges inside and air will not flow smoothly.

Have a look at the Floor section of my rebuild site, link in sig. It shows one example of heat ducts. There are many other ways they do it.