HELP, gas heater not working

I have a Modine 250,000 BTU natural gas heater in a 30 X 100 green house. It is filling the GH with smoke and has soot all on the heater. We replaced the vents(smoke stack) because the gas company said it isn't "drawing" properly. It's still not working. It's heating the green house, but the smell and soot is awful. What could be wrong and why after 2 years, did it decide to do this? (especially when it's supposed to be in the single digits tonight?)

Susie, I don't know a thing about heaters, but I am praying for you. This is awful, and there's not another thing I can do. I'm praying for your help to come too!!

duh, Johnnie works in heat!! He said sounds like the heat exchanger is cracked. Buy a new heater :(

me again, nothing blocking vent??? sounds too new to be cracked unless something happened to cause it. (from Johnnie)

when did you replace stack???

Replaced it today after the problem was discovered. The heat exchanger isn't cracked (as far as we can tell) Bill went back this evening in the dark to see if it was. That's how we found the last one cracked and why this one is so new. Couldn't find anything in the vent.

sure wish we had a clue. I am still praying though, cause I know that's a big profit maker.

Gas and air mix? is it burning yellow or blue?

It's burning blue.

Johnnie's lost, he was certain it wouldn't be. I'm sorry, I sure wish we could do something to help

Bill and Steve are going to take the stack apart again tomorrow. I hope they find out what is wrong, I don't want to have to wash those ferns!!

better than losing them though!!!

check down inside heater where stack connects to heater.

He will check, thanks. I have to come to Atlanta to get my DD today, she is home sick.

oh susie!!! that ride again so soon. sorry, maybe next week you'll get a break!

I hope so, I wanted to come visit you again!! I'm going to just go and come back since they are calling for snow. This may be for the best, since it's supposed to be bad all week.

well, if the snow looks like it's going to move in, just come south and have collards and black-eyed peas with us!! please do be careful, you know how us Georgians drive when they say the *S* word!!

Yeah, about like the Tennesseans!!! "Okay Bubba and Billy Bob Joe, lets see if we can do one of them donuts here in the middle of the road on this ice." "Shore Clem, lets see ifn we can do a hunert goin down that hill and stop at the bottom."