Flex Pipe for Majestic (or Vermont Castings) 300 DVB

[skieratpsu]

Installing a used gas fireplace in basement corner. Need to vent straight up and then elbow through the rim joist. Fireplace only came with 18" of 4 x 7 rigid pipe (they had it installed on an exterior wall straight out the back). To me, it seems like my lowest cost option would be to use one length of 4 x 7 flex pipe. The manual seems to allow this, but of course says to use the expensive Vermont Castings only pipe. I don't see why I can't just buy something like this and be done with it.: http://www.woodstoves-fireplaces.com/napoleon-5-ft-vent-kit/

Does anyone see a problem with that? Relevant page from the manual is attached. The only think I'm worried about is the spring spacers that keep the smaller pipe centered. Doesn't seem to come with those.

I can't fine anywhere to buy the Vermont Castings (Majestic) brand flex pipe. I see it here in a kit (which i assume has the springs, but the price is way higher than the napoleon linked above. (broken link removed to http://www.woodstoves-fireplaces.com/majestic-up-out-flex-starter-kit/)/

Thoughts?

(broken image removed)

 

[DAKSY]

What brand is the rigid section you got with the unit?
It might be best if you ran more of that instead
of mixing flex & rigid.

 

[skieratpsu]

It is Duravent. It seems like the rigid is much more expensive (need 3 90 elbows), plus 3 lengths (including the one I have). I'd like to use no rigid and only 1 piece of flex. The manual indicates that you can bend the flex 90 degrees, so I wouldn't need elbows. I can get the napoleon flex for $70, whereas the 3 elbows and two additional rigid pieces would total about $350.

 

[DAKSY]

You should be able to reposition the adapter on the fireplace so that it becomes a top vented unit rather than a rear vented one. That will eliminate one elbow.
The problem with the different manufacturer's venting you want to use is that it hasn't been tested for use with your fireplace.
Common sense may say that 4"x7" venting is 4"x7" venting, but you are putting fire & a deadly by-product of that fire in your house.
One error in the assembly of mismatched, untested components & that deadly by product could leak into your living space.
Do yourself & your family a favor & install this correctly.