flue size for gas conversion

Billy March

Back in the day (late 70's early 80's) I did alot of work for a shop that was an authorized installer for BUG. That was when you would convert oil fired boilers to gas. WE would run the gas line, vaccuum out the old boiler,downsize the flue pipe and install a gas conversion burner. The gun I am involved with right now is an Economite 400.It's probably been over 15 years since I did a conversion without changing the whole boiler,but I don't remember what size flue pipe we would reduce to. The customer seems to be having a problem with the pilot light blowing out sometimes.I think she might have a possible problem with the chimney(brick with clay lining)but I want to redo the flue pipe first because it still has the original 8" flue from the oil boiler with the barometric still attached. After I do this ,if she still has a problem I want her to have her chimney inspected but I don't know of a reputable chimney company. I want to instill new flue pipe and remove the barometric and install a horzontal diverter but I don't remeber what size the E400 required. Does anybody know what size flue these conversion burners required?

Dale

Varies

Since the economites have variable input ranges the vent connector size will vary. These conversions need to be set up with a gullitine flue restrictor using a CO2 meter to be accurate. If you don't besides dangerous CO readings you'll get bad overfire draft and wildly high stack temps. You should always have a barometric on these. Timmie I think puts the flue restrictor after the barometic, we follow the old bacarach rule of putting it before. Contact economite for a copy of the original install instructions or better if you're near RhodeIsland take the conversion class from Timmie.

Ranger

I agree with Dale..

..as a "rule of thumb" I was taught many,many moons ago takeing into consideration that it is assumed that you have the correct imput rate orifice installed that on an older open pass (like a porkchop) boiler you would downsize the flue one size from the origional (i.e.origional breach was 7" you would re-run in 6") to compensate for "overdrafting"
w/the new gas gun but remain the same size for a tight (like a pin,close pass) boiler."double-swinge" barometric damper a must.As always,follow the manufactures instructions above all else.I think Fields Controls has some training literature on this subject also if I am not mistaken.

Unknown

Billy, the sizes

are

250,000 BTU 7"

320,000 BTU 8"

400,000 BTU 9"

Remember however there are many things that can cause pilot outage other than flue size and chimney problems. Have you taken a set of millivolt readings? Have you done a combustion test? The burner itself may need cleaning as the squirrel cage on those are known to get plugged with dirt and dust.

If you are interested I have a complete manual on gas conversion burnersand combustion analysis.