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Insulate exterior 4" ducts from air heater

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  • Insulate exterior 4" ducts from air heater

    I'm just not sure what to use to insulate and protect the outside inlet/exhaust 4" ducts from my solar air heater that will be piped into the window. I'll be using round metal duct pipe or aluminum dryer vent pipe. There's a million articles and videos about making a solar air heater but no on talks about the ducting.
    Your info is much appreciated!!!

  • #2
    How long is the run ?

    How big is the collector system area ?

    What's the ave. temp. diff, ambient to heated air ?

    Whatever you use, make sure it's service temp. is high enough, it will withstand the elements. including UV, water, freezing, wind, critters, etc.

    Don't use what's commonly referred to as duct tape. The stuff won't last.

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    • #3
      And be sure to plan for stagnant air temps, if the blower motor stops, or a vent gets plugged. Then it starts heating without dumping the heat....
      Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
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      • #4
        The ducts will be about 4' and 10' long. The heater box is 4'x6'. Here in NW S. Carolina it usually stays in the 30s and 40s in the winter. So what can someone suggest for wrapping the ducts and waterproofing??? Thanks!

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        • #5
          Originally posted by Mike90250 View Post
          And be sure to plan for stagnant air temps, if the blower motor stops, or a vent gets plugged. Then it starts heating without dumping the heat....
          Gotcha!

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          • #6
            Originally posted by J.P.M. View Post
            How long is the run ?

            How big is the collector system area ?

            What's the ave. temp. diff, ambient to heated air ?

            Whatever you use, make sure it's service temp. is high enough, it will withstand the elements. including UV, water, freezing, wind, critters, etc.

            Don't use what's commonly referred to as duct tape. The stuff won't last.
            No duct tape.

            Comment


            • #7
              Originally posted by skizman View Post
              The ducts will be about 4' and 10' long. The heater box is 4'x6'. Here in NW S. Carolina it usually stays in the 30s and 40s in the winter. So what can someone suggest for wrapping the ducts and waterproofing??? Thanks!
              Not one suggestion about what type of insulation to use to wrap the ducts on the outside????

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              • #8
                try "Armstrong armor flex" its a foam rubber insulation for pipes available in diameters or sheets. For long outdoor life its often wrapped with a fabric and painted with something.
                Wayne, Virginia, usa.,13kw tracking gt.

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                • #9
                  There's not a lot of DIY stuff for covering exposed outside air ducts but the Armaflex can work as well as rigid fiberglass insulation boards. Both must be covered with a protective jacked or cladding to be rain-tight and survive long-term. The insulation we sell at work is not intended for home use but easily survives the high temps and does not turn to goo as it ages like some foams.

                  We apply a self-adhesive, multi-layer foil jacket on the outside to mummify the installation and protect from UV, hail and such. The self-adhesive exterior covering is made by Ventureshield. You're looking at several hundred dollars at least for what we offer but it normally only goes into biopharma plants and food process areas where they demand fiber-free, plenum-rated insulation products. We sell our TechLite melamine foam insulation through Grainger and McMaster-Carr if you want to price it out but I think you are better off with a rubber, closed cell foam like Armacel or similar product from Namaco.

                  Dave W. Gilbert AZ
                  6.63kW grid-tie owner

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                  • #10
                    Originally posted by skizman View Post
                    The ducts will be about 4' and 10' long. The heater box is 4'x6'. Here in NW S. Carolina it usually stays in the 30s and 40s in the winter. So what can someone suggest for wrapping the ducts and waterproofing??? Thanks!
                    What's the duct diameter or cross sectional area and shape ? round/square/rectangular ? Armaflex or "Armacell" is good stuff but not cheap. It's also available in sheets of varying thickness with cladding on one side, adhesive on the other. It has an insulating "R" value of ~ 4/in. It's pretty impervious to water, but must be protected from sunlight as it will quickly be harmed by UV. Depending on the air temp. inside the ducts, 2" thickness will probably suffice. The drawback is the upper service temp. for Armacell is ~ +180 F. The upper service temp. for armacell is, for some reason, higher at +220 F. An air collector may operate at close to that that +180 F., but that would be a poor domestic HVAC design. More likely, a power or blower failure would cause stagnation temps. higher than that.

                    I've had 1" thk. Armaflex on outside piping for my solar water heater and habe it wrapped with aluminum (not cloth) duct sealant tape. No breaks or failures after 8 years of continuous and daily service. But,- it is protected by the alum. tape and not exposed to sunlight.

                    Google "Armaflex" and/or "Armacell". Like I wrote, and not a plug, good stuff, fit for service, durable and trouble free.But, you want nice - you pay nice. One thing: If you use it, compress it about 3 or 4 %, it'll tend to shrink a bit and contract. over time. Edge gaps, separations and exposed areas that are not insulated can be a much bigger heat robber than they look or you may think.

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                    • #11
                      Thank you for taking the time to pass on all this info. I can't afford the Armaflex or Armacell. I'll just have to do the best I can from the main home builder chains.

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                      • #12
                        Originally posted by skizman View Post
                        Thank you for taking the time to pass on all this info. I can't afford the Armaflex or Armacell. I'll just have to do the best I can from the main home builder chains.
                        I appreciate where you're at. Been there. Lots. Unfortunately, cheap insulation, like fiberglass batts, etc. will waterlog with either direct water ingress or vapor condensate if not surrounded w/ a vapor barrier. What are the duct dimensions ? And round or rectangular ? The heat loss may not be very large compared to the amount gained by the collectors. Gimme' some dimensions to work with.

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                        • #13
                          I would use some some foam, like the pool noodle type. Cheap and easy to come by as packaging a lot of times. Use a larger diameter metal pipe to go around it for further protection. Or use a better insulator if that's not good enough, with a metal larger-diameter duct around the inner one. Shoe Goo, or amazing goop or other Miracle glues I have luck with outdoor applications.

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                          • #14
                            Originally posted by Brian53713 View Post
                            I would use some some foam, like the pool noodle type. Cheap and easy to come by as packaging a lot of times. Use a larger diameter metal pipe to go around it for further protection. Or use a better insulator if that's not good enough, with a metal larger-diameter duct around the inner one. Shoe Goo, or amazing goop or other Miracle glues I have luck with outdoor applications.
                            Safety first. Just be careful of temp. limits and offgassing. Noodle foam may melt. If the duct is round, whatever you put around it can be wrapped with a larger AL duct. Just split the outer wrap lengthwise and strap it together. It'll be reasonably water tight if not a vapor barrier. Again, just watch offgassing and temp. limits. Always think safety.

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                            • #15
                              Yeah that pool noodle foam doesn't sound dependable. So this is exactly what I did. I wrapped the metal ducts with 2" duct wrap insulation. Then used foil/foam duct wrap with two wraps. I tried two different 3M foil tapes and neither would stick on that shiney foil/foam wrap. I'm talking about the long edge of each wrap where it ends. The tape just won't stick good, so I wound up wrapping the entire ducts with the foil tape like a candy cane. Then I will coat the ducts with elastomeric roof seal. That's some great stuff. Then I'll probably use some old tarp to wrap it all just for more protection from the rain or snow. Gotta do whatcha gotta do!!
                              I appreciate you guys offering a helping hand!

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