Insulated Ductwork

[wewantutopia]

Hi guys,

So I have finished my solar air heater panel and am ready to hook it to the house (I'll create a seperate post in the future describing it etc).  I have it placed against my south facing front porch and to get the heat into the house it needs to run through about 5 feet of duct work (both ways).  I am looking for opinions.

I am considering this: menards.com/main/heating-cooling/ductwork/flexible/4inch-x-25-flexible-insulated-duct-black-jacket-r6/p-1390982-c-9503.htm

I am questioning this because 1 it is only r6 (I'm in Chicago) and 2 it is a flex line.

I was hoping to use rigid ductwork, to minimize resistance and slowdown inside the duct, and cover it with some sort of xps duct insulation (maybe 2 inch xps for r10) but I can't find anything like that.  My inlet and outlet are 4 inch. 

Does anyone know of a product like this (the ridgid foam over metal duct)?  Or, what do you think of using the product linked or something like it?

Thanks!!

[thirteen]

Contact a boiler repair company in your area or an furnace co. and see what they have. They do make insulation that goes on piping that splits open and folds around the pipe I work on asphalt plants and all of their pipes are wrapped. You could put the 4 in PVC pipe inside a larger pipe and just use the cans of insulation foam between to insulate it after you center it. You will need to check the heat range for the pipe. Just an idea to ponder. 

[birdhouse]

I was hoping to use rigid ductwork, to minimize resistance and slowdown inside the duct

my HVAC guytries to steer clear of the pre-insulated flex stuuf, purely because it slow down the airflow sooo much.  he runs mostly rigid metal, hand wraps it with as fiberglass as he sees fit, then duct tapes some tyvek type barrier over the top to keep it all tight and clean. 

thirteen's idea with pipe in a pipe with spray foam (great stuff) in between is a great idea.  you could even use snap link metal 4" (for heat reasons) with 6" pvc around that.  drill holes in pvc to get even foam insertion spots.  sounds like a winner to me.

adam

[wdyasq]

There is a question or two that may or may not be relevant. Will it hurt to loose the heat from your collector?  IF your heat goes from the porch, through a wall into a place where the heat is needed, who cares if the duct is insulated?  If it goes 5' in ambient in CHHHHHH...icago, you may not get any heat from your panel.

Birdhouse has a decent idea, although you will want as much insulation as practical. A 4" pipe surrounded by a 6" pipe gives 1" space to insulate. The BEST rigid insulation is ~R7 per inch.

At one time, there was available a fiberglass board that could be cut and folded. A few layers of that would work well. Or, one layer of foil/fiberglass and more layers of good rigid foam, overlapping. One 4' X 8' sheet of 3/4" rigid foam would make a lot of 4" duct cover.

Ron