too much vertical rise?

[DavidinVirginia]

I've have planned 26' vertical rise through 4" pipe up through an exsting (otherwise unused) chimney flue. reading back through the pellet stove manual I found where they say recommended max is 18'. What happens if i have too much vertical rise?

 

[johneh]

The best way I can think of to put it try blowing through a 25 ft. garden hose
same effect for the combustion blower

 

[Former Farmer]

I would think that you might get too much draft with the hot air pulling in combustion air as it rises up the venting. You may have to install some sort of damper to set your draft.