DIY Outdoor boiler heat exchanger

[AK Steve]

Those of you who have built wood boilers, what did you do for the heat exchanger inside the boiler? I've thought of several ideas, but they all get expensive fast when you include all the giblets and gravy.

 

[Matfam]

Copper is probably the easiest thing to use. I’d caution you on building any type of boiler DIY... Water expands 1600 times in volume when it changes state to a vapor. If you don’t have a particularly strong grasp of what you are doing, this will be dangerous.

 

[NSMaple1]

Heat exchanger inside the boiler? Not sure exactly what you mean there. Usually boilers are either simple water jacketed things where the firebox walls exchange the heat to the surrounding water (inefficient heat exchange), or there are tubes inside connecting the firebox with the smoke exit, all surrounded by the boiler water, that exchange the heat to the water (crud up easily so frequent cleanings required - need to be designed for easy cleaning). Made usually of the same material as the firebox I believe.

 

[cantoo]

Mine has rectangular tubes inside at the top that allow the flames to surround them and heat the water. They work well even though there is a pile of fine ash dust on top of them all the time. There is a good exchange of heat to the water on the bottom and sides of the tubes. I'm slowly gathering all the materials to build one. Intend to build it about the same design and same size as I like the one I have now. Mine is a Pacific Western and is a stainless model. My new one will likely be regular steel. I just noticed a tiny crack in mine where the smoke bypass rod slides into the burn chamber. My son has a tig welder so we'll clean it up and weld it in the next couple of weeks.

 

[cantoo]

And I'm assuming you mean a open system wood burner and not a closed system wood boiler so steam won't be involved.

 

[AK Steve]

Copper is probably the easiest thing to use. I’d caution you on building any type of boiler DIY... Water expands 1600 times in volume when it changes state to a vapor. If you don’t have a particularly strong grasp of what you are doing, this will be dangerous.

I don't intend to cross the phase envelope, but it's certainly possible. The calculations are pointing me well away from that much temperature increase.