Flue sizing question for EKO

[James Ascherl]

I have a EKO 40. I am going to drop a stainless steel liner down my chimney I have to go up about 24'. My chimney is in the very center of the house and has 6x10 clay liner. My questions are:
#1, Can I run a 6" flue even though the manufacturer demands an 8"? If I recall, many EKO owners reduced theirs to 6".
#2, If I can run the 6" flexible liner, how important is insulating the pipe, keeping in mind that the chimney is in dead center of my house?
#3, If I can safely run the 6", where is the best place to transition from the 8"? (I have to run approx 8' horizontal to chimney)

Thanks as always for any and all input.
Hope everyone is enjoying the summer.

 

[Duetech]

I have an EKO40 Super (older model) and ran it with 6" and transitioned from the "near" 8" to 6" right at the outlet via a custom built a reducer. My older unit did not come with a real 8" opening as it was a metric size and I did not like the way that 8" pipe fit the outlet. Technically speaking your inspector and code and insurance comapny and the boiler manufacturer will probably have a lot to say about using straight 6" instead of 8". My manual did not "demand" 8" and even listed 6" as viable (though 8" seemed preferred) so warranty was not an issue there and the insurance company accepted the installation and issued a policy.
Physically, if your fire tubes are the same as mine, the 6" will work without constricting needed air flow. My unit has 8 near 2" diameter pipes for the heat exchanger which equate to a little over 25" of area for air flow and a 6" pipe has a little over 28" of area. The nozzle is only about 8" of area but is host to a lot of expanding gasses and the resident turbolators in the heat exchanger only restrict air flow a little because those expanded gasses are already cooling and contracting. However if your unit will idle then you will run the potential risk of creosote and ash build up which will reduce or constrict the air flow of your chimney. My unit idled a lot so I had to clean the chimney frequently (1x-month) due to ash build up though creosote was never a problem except at the top of the chimney where the chimney was the coolest and the rain cap would drip condensate (messy and undesired). A straight burn with storage would probably eliminate that altogether. An 8" pipe will yield just over 50" of area and will not be as prone to clogging and restricting air flow. It's been a while since I looked but I believe that the mfg requires 18' minimum draft as well and the length of the chimney will effect the draft.
My 6" was triple walled insulated duravent and was "T" 'd to one short 10" piece of 6" black pipe that came out of the boiler that was non insulated pipe. One other 6" pipe came out of the bottom of the "T" where a barometric damper would go but basically it was a repository for ash build up. I always ran triple walled as soon as I could hook up to it as I like the way it stays warm inside and reduces the creosote build up. I don't like the thought of uncontrolled fires.
Your 10" x 6" clay presents an insulation problem and might require a custom fit.

 

[James Ascherl]

Thanks Cave for your input. I am running with 990 gallons of storage so hopefully I will eliminate some of the issues you mentioned. I should mention that the EKO is replacing a Timbereze wood burner (It had a water jacket and was hooked to the house to assist the oil boiler). The EKO is going in the exact same location so the venting is virtually the same, however, The Timbereze was straight 8" single walled, and was just shoved into the clay liner. That was in use for 30 years without any issues. I do not feel comfortable running the EKO straight into the clay liner so I will have to reduce it. I don't think I can squash a 7" pipe enough.
What is the best way to clean a chimney. I have a very steep slate roof that is three stories up, so cleaning from the top down is not practical.

 

[Duetech]

To be honest I can't say much about the Timbereze but from the sound it probably had a hotter exhaust than the EKO is intended to have at full operation (400*f). The exception to that is at start up where the EKO would probably be comparable to the Timbereze.
With a wood burner I had I had to go from the top down to clean the chimney. With the EKO I had the "T" which went straight up from there and since the exhaust outlet of the EKO is high enough I used the wire brush and a chimney rod kit. Inside the house I think you might need to "mod" the chimney cleanout to allow you to angle the chimney opening for the brush and rod assembly to enter the chimney. The other alternative is to find a reputable chimney sweep. With the EKO running to heat storage I think you will find that your burns are going to be long enough that they are going to leave the chimney rather clean. At full gasification my EKO looks like it's burning natural gas and not wood and all that can be seen is steam exiting the chimney. The ultimate secret for clean burns with a gasifier is dry, dry and dry wood at a moisture content no greater than the mfg suggests. Cleanout times should find themselves further apart as a result.