Wood Boiler Efficiency

[DaveBP]

So I see the pictures of the Garn side vent flues coming out the wall and dripping into the barrel.

What do you do with all that "molasses" in the barrel?

 

[heaterman]

why are people saying such great things about the mod-con gas and oil boilers - what are they doing that allows them to condense at high temps that the wood boilers can’t do?

My understanding of gas mod/cons is that the exhaust gas is exposed to a second heat exchanger surrounded by the cooler RETURN water after passing through the SUPPLY water that all the standard boilers use. But with a typical baseboard system the return temps may not be low enough to get efficient condensation. Radiant systems (and snow melt for sure) would get better use of all the extra cost of a condensing boiler, I think.

Exactly right on the return water temp. There are some variations on that design however. Many of the mod/cons on the market use a Euro designed and built HX from Giannoni (sp) that basically only allows condensing to take place in about 1/3 to 1/2 of the HX. By contrast, the HX in the Viessmann design is capable of condensing on its entire surface. Even a baseboard system can be coaxed into condensing mode with proper use of a reset control that keps water temps low in the milder parts of the winter. Probably 75% of the BB systems I see will work quite nicely at reduced water temps in all but January/February type weather.

 

[heaterman]

So I see the pictures of the Garn side vent flues coming out the wall and dripping into the barrel.

What do you do with all that "molasses" in the barrel?

Never encountered someone that had to empty one. It's basically just water vapor that condenses when it hits the cold atmoshpere. The primary function of the barrel is to catch any hot stuff/embers that may make it all the way through. Garn's move a LOT of air.