Ducting length?

[vantastic]

I've installed a Truma 4e and I'm currently running my ducting. There is one length in particular I'm a little bit worried about. It's the longest run by bar at about 5m and it has several 90 degree bends. I'm trying to get an understanding of maximum length and maximum number of bends.

This run will require me to drill through a couple of panels I really don't want holes in unless the duct is going to go through so I can't easily test this before committing.

The duct is going to the sleeping area so keeping it a small bit cooler than the rest of the van is ok but I also don't wan't to lose most of the heat in the duct.

 

[vantastic]

Yeah, I've read it. Still asking the question.

 

[MikeD]

I am no expert on Truma but I can tell you that the approx 3mtr run to the front of our van means the air is decidedly cool and has a pathetic airflow.

Sorry I have no idea how many bends it has along its length.

 

[vantastic]

Ooh, 3m and cold air? That's not ideal.
I may have to significantly change my plans in that case.
Are the ducts insulated?

 

[MikeD]

Ooh, 3m and cold air? That's not ideal.
I may have to significantly change my plans in that case.
Are the ducts insulated?

I just had a quick look but I can't see them.

It's a IH PVC so I suspect not.

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[Mike800966]

Our longest lengths must be about 5m using what looks like 3" duct. When the fan is running at slow speed there is not a lot coming out the furthest end and most of the heat has been dissipated but when the fan runs harder it is a quite useful amount of warm air.
I should ring truma technical and ask them alternatively you could try to work it out from the back pressure figues for the duct itself.
Try to insulate the ducts whee you can, but not under shower floor or wardrobe of course!
Mike

 

[vantastic]

Not under shower floor and wardrobe? Why not?
I will be running this under the shower tray and being right on the floor that was one of the main places I was concerned about.

 

[pappajohn]

Could you utilise a 3" computer fan (or sized to your duct) somewhere within the 5mtr run to increase flow.
If the air is travelling faster it will retain more heat.
Shouldnt take much to design a housing for it and wire it back to the heater fan.

 

[Reallyretired]

Our longest run is about 6m with 5 outlets (two permanently closed in external lockers) and at least two rightangle bends. Airflow from the end is zilch

 

[sallylillian]

I had 2 Truma Saphirs on the Flair, admittedly I am commenting on cooling rather than heating but on one unit there were 2 off at least 5 metre runs to the pelmet which then had 4 off vents. Basically it was crap. Airflow just noticeable and cooling virtually useless. I would imagine the same would be true for heating.

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[Mike800966]

Sorry, perhaps I didnt type it right but I meant to suggest that you do not insulate the duct under the shower floor or the wardrobe! Our Lunar has the duct encased inside the rear underbed locker, I have always had those vents closed off but I think the design is that even when the flap is closed, there is stil a very little air which leaks out and it does work to dry out anything damp in that large locker.

Also, I added a electric hot water kit some years ago and the truma is under the bed. When its really cold and we are on hookup, the water heating element is quite enough to keep us toastie!

There have been several discussions about how to control the Truma from a distance, using an extra switch, well worth it if you arrange things to be able to turn on the hot air heater whilst still under a warm duvet!
Mike