Forced air diesel heater ducting insulation.

[Sam Woodbridge]

Hello, I am planning to insulate my Webasto diesel heater ducting that runs throughout the sailboat. I'll pull the ducting to install the insulation. Any advice from anyone on an easy way to do that?

I also plan on buying this https://www.heatso.com/thermoduct-in...-ducting-hose/ from heatso. My question is what tape would someone recommend? I believe these insulated pieces come in two half foot lengths. They will need to be taped or stitched together, and I believe I read that it is recommended to tape the inside of first few inches to get the insulation to slide easier.

Anyone have any recommendations or has anyone did this to their boat?

Thank you - Sam

[wrwakefield]

Hi Sam,

What you found would likely work, but I wonder if it might absorb water via condensation, etc?

I have had very good success using Reflectix to insulate my forced air heat ducts on the boat [as well as under headliner panels agains and exposed hull in cabinet backs, etc.] You can double it up quite easily as necessary.

Instead of removing the ducting, I loosely [an air gap is needed between the radiant barrier and surface to be insulated to gain max benefits…] wrap the duct [in 24” increments] using 24” wide Reflectix; and tape the seam with quality aluminum foil tape [2” wide tape is sufficient.]. Then I slide the 2ft section along the duct toward blind spots I cannot reach, and install another 2ft section- overlapping and taping it around the circumference of the previous Reflectix tube. Then slide both into the void until I hit a bulkhead, fitting, etc; then repeat.

The basic process is shown in their brief video re: ductwork.

In case this approach is of interest.

I can say you are on the right track as insulating the ductwork- especially where it runs near/on the hull- improves efficiency tremendously.

Have fun with your project.

Cheers, Bill

[MerMike]

I used 4" flexible duct insulation, purchased from the local big-box hardware store. I taped it with the above mentioned foil tape.

The main reason I insulated was that the duct ran right under the reefer. It worked well. The reefer is cool and the furnace output is hot.

[Sam Woodbridge]

Thank you for the post Wrwakefield. It was exactly what I was hoping to learn on the forums. I’ll look up Reflectix and watch the video. I’m almost 100% positive thermoduct is waterproof. At least on other websites it does state thermoduct is waterproof. I’ll get clarification if I do choose to use thermoduct.

Mer Mike thank you as well!

Sam

[GordMay]

Proper ductwork insulation is essential, for optimized efficiency of your HVAC system.
I recommend a foil or vinyl faced [vapour barrier*] thermal insulation, with an R-Value of R-3.5 -to- R-6 [or higher].

This usually requires a minimum of 1" thick, UN-compressed, insulation.


* Not radiant barrier.
A static air gap [void], of 3/4" minimum, is required, for a radiant barrier to avoid conductive heat transfer.
See:
“Super Insulation - Ideas?”
➥ https://www.cruisersforum.com/forums...tml#post248574
➥ https://www.cruisersforum.com/forums...tml#post243930

“Air Space Requirements”
➥ https://cdn.reflectixinc.com/wp-cont...s-Rev-0219.pdf

[Sam Woodbridge]

Thank you GordMay.

Sam

[NorthCoastJoe]

I second Reflectix, easy to work with.

[Sam Woodbridge]

Thank you for the second on Reflectix - NorthCoastJoe!

Sam

[GordMay]

For HVAC duct insulation, I recommend using a foil-faced, closed cell, polyethylene foam insulation, like ‘Armaflex’, etc, with a minimum R-value of 3.5.
I do NOT recommend radiant barriers, like ‘Reflectix’, which simply don’t work, in this application.

Any reflective radian barrier [including Reflectix] MUST be used with an air gap, lest the reflective surface become a conductive source of heat transfer.

Originally Posted by Reflectix

"No Air Space = No Reflective Insulation Benefit."

Reflectix has little, if any, R-value, when installed, the way most folks do it [directly on duct, without spacers].
Even when installed properly, it has a much lower R-value than “mass” insulation.

[Sam Woodbridge]

Thank you for the second post GordMay.