Hahha, funny about Europe. I grew up in eastern Europa. We had a boiler but it was much bigger like you said than when I have now. I think these OWB are too small. Our's were more like the Garn units. You just lit it every two days. It held about 2000ga water and stored a lot of heat. They were coal and wood fuel.
My NCB 250 coal is "rated" for 6000sqft, our house is 4000sqft. I have 0F drop from the OWB to the house; the line is well insulated the ditch is 6 1/2 foot deep.
However, when my blower runs, my water temp drops a lot. Pretty big swings. So, I was thinking to instal the tank in the basement like you said. I figured my central heat blower runs about 10 min avg; the water pump is 20 gpm on high; so in one heat cycle about the entire boiler water is circulated, and the boiler water temp drops about 10+F. So, if I could add 100-200ga like you said, may be I could prevent the swings being so bad.
Otherwise my boiler has been working great for 3 seasons now.
I'll try to get a tank around 150-200. May be a domestic water heater tank.
What kind of tank did you use? I wonder what else could I use other than a water heater tank? would a new oil storage tank work?
Like this;
http://www.uniquetruck.com/p-28285-roth-eco-double-wall-tank-165-gallon.aspx thanks
european style boilers use huge tanks they load up with heat kind of like a batch burner.
imo 50 gallons is not enough,but i have 275 and for my boiler it kind of big``ìmo``again
in the 100 to 200 range seems not bad.my dad installed 200 on his boiler and recovery times are good
and temp swings are alot less wild.
also a semi nude tank makes one heck of a radiator if you got a cold basement.
don`t forget if the basement is cold,the whole house is cold
alot of people are not keen about external tanks on this site for there own reasons,but i have had good luck with mine.
the europeans are way ahead of us when it comes to wood boiler heating and i feel there ways are good examples to follow
just my opinion again
good luck