What rise do I need in my ducting, for gravity heat flow for Kuuma VF100?

[motoguy]

Planning the ductwork to tie the Kuuma into my existing (propane) furnace ductwork. What slope/rise do I need, in order for the Kuuma heat to safely "move" in the event of a power outage? I found this for plumbing, but I'm now sure how it works for ductwork:

2 1/2" or smaller 1/4" per foot
3" to 6" 1/8" per foot
8" or larger 1/16" per foot

It looks like the main trunk line from the Kuuma plenum, to the (propane) furnace plenum, will be 21" x 9". This size seems to work with the clearances I have available, the width of the existing trunk (21.5"), as well as the 180-200 sq/in of volume needed for the Kuuma.

Will 1/16" per foot suffice? Total run will be 26'. 9' from Kuuma to wall, turn a 90, then 17' to the tie in at the existing furnace. The 17' run will be directly underneath the existing trunk line (too small to want to tie in to the end of the existing trunk...so I'll just run under it, and tie in near the existing plenum). I'm running on pretty tight clearances as is (keeping 1" between trunk line from Kuuma and combustibles after 9'...will have 6" from Kuuma to 9' mark), so I need the least slope that will safely do the job.

 

[brenndatomu]

I believe that 1/4" per ft is considered minimum (the more the better) I could be wrong though. I'm sure @STIHLY DAN will know. You could always install a safety heat dump door in the plenum if you can't get enough rise...http://www.yukon-eagle.com/FURNACEACCESSORIES/SAFETYHEATDUMP/tabid/200/Default.aspx
Sounds to me like this would really be a good idea anyways since you are tying in so far away from the Kuuma

 

[STIHLY DAN]

You don't need any slope, you are not draining the air. You only need the ductwork large enough and enough outlets. I don't like the long run to tie into your propane unit, you may want to increase HP if you go that route. If you are running underneath existing ductwork why not just run new takeoffs? That way there is less static pressure and no need for backdraft dampers.

 

[motoguy]

Didn't get the ductwork replaced last year, so lived without the Kuuma last winter. Finally got the ductboard/flex replaced with metal (main trunk line, as well as all branches), and the tie-in system for the Kuuma. I'll post some photos tomorrow. We followed Kuuma's requirement, with 6" (actually, we gave a lot more) for the first 6' of service plenum, and 1" after that. The whole trunk line is at least 1" from combustibles, but some of the 6" branch lines are in direct contact with the romex in the joists.

Fired the Kuuma for it's test run tonight. So far, it's doing well. I need to install my manometer in the flue, so I'll do that after letting it die down tomorrow. Then I'll seal the flue seams up well with stove sealant, and / or seam tape. Our flue is an external add-on affair, so I'd like to give it all the help I can. I've got a 90 coming out of the back of the Kuuma, into a 45 through the concrete foundation wall. Then a 90 up, with a couple of 45's to clear the roof overhand. We haven't had a flue/smoke problem (other than at startup) with the wood stove before (Arbor Avalon), but...if I can do a little bit of work to help it out, I'd rather do that.

 

[Bootstrap]

That's a lot of angles with the chimney pipe, if I understand you correctly. But if theres no other way, then theres no other way.

 

[motoguy]

That's a lot of angles with the chimney pipe, if I understand you correctly. But if theres no other way, then theres no other way.

Here's what I have going on, from exit of Kuuma to the top.

 

[motoguy]

You don't need any slope, you are not draining the air. You only need the ductwork large enough and enough outlets. I don't like the long run to tie into your propane unit, you may want to increase HP if you go that route. If you are running underneath existing ductwork why not just run new takeoffs? That way there is less static pressure and no need for backdraft dampers.

Here is how it ended up.

 

[Bootstrap]

Its kind of ballsy to have a baro damper on a wood stove. If you ever had a chimney fire it would rage out of control quick.

 

[JRHAWK9]

Its kind of ballsy to have a baro damper on a wood stove. If you ever had a chimney fire it would rage out of control quick.

This is not a wood stove to begin with. It's not ballsy at all on wood furnaces.....they are actually required on most.

It's a Kuuma, you practically don't even have to clean the chimney, must less have to worry about a chimney fire.

 

[brenndatomu]

Its kind of ballsy to have a baro damper on a wood stove. If you ever had a chimney fire it would rage out of control quick.

.they are actually required on most.

What he said ^ ^ ^

 

[maple1]

^^ x2.

 

[Bootstrap]

So it doesn't burn wood?

 

[maple1]

All wood burners are not stoves.

Most furnaces & boilers spec baro dampers so as to maintain constant draft specs, automatically. And very little chance of a chimney fire with clean burning furnaces & boilers. I am heading into winter 5 with mine, haven't had a brush in my chimney since summer of 2012. I know guys around here with older wood furnaces (i.e. not newer 'cleaner burning' ones) who also haven't had to sweep their chimney for years. So running a baro on a wood furnace is hardly 'ballsy'.

 

[Bootstrap]

Good to know. I cleaned my chimney this year. It wasn't too bad. I could've not done it.