Water to water heat exchangers and wood furnaces

dlabrie · Nov 28, 2004

I have been researching outdoor wood furnaces. From what I can see, there are 2 basic types, pressurized and atmospheric (non pressurized). A pressurized system would hook up directly to my FHW system to make a closed system. An atmospheric system would transfer heat via a Flat Plate, water to water heat exchanger. This would keep the 2 systems separate, hence avoid any contamination/corrosion issues associated with atmospheric systems. My question is, How well do the exchangers work? I realize they can't be as effective as a direct link to my FHW system, but are they close?

Also any opinions on outdoor wood furnace brands would be a great help.

Thanks,

Mackinaw · Nov 28, 2004

I've been considering an outdoor furnance myself. I would think you would want a water to water heat exchanger no matter what. If you have an open loop system, wouldn't you still need anti-freeze in the system? I just starting to look at these so I'm not sure. Either way a heat exchanger would allow you to transfer heat to your FHW system and your domestic hot water. Use one exchanger for all your hot water needs. Heat exchangers are expensive, but they work if sized correctly. An open loop system would have a minimum of 160 degree fluid. With a properly sized exchanger you should have no poblem getting all the heat you need.

brad_oatley · Nov 28, 2004

What will you do with the excess heat?

dlabrie · Nov 28, 2004

There isn't much excess heat. The wood furnace closes down when there is no call for heat. The hot water stays stored in an insulated water jacket. When the system calls for heat, the vent on the wood furnace opens, a fan comes on and the fire comes to life to heat the water. It runs just like a FHW boiler, but with wood.

Birdhunter1 · Nov 29, 2004

I use to work for a sheetmetal contractor that carried these. They wren't a big money maker and we didn't put alot of them in but we did sell and service them, they work good too.
Hardy woodburners.
http://www.hardyohio.com/

thcri · Nov 29, 2004

( There isn't much excess heat. The wood furnace closes down when there is no call for heat. The hot water stays stored in an insulated water jacket. When the system calls for heat, the vent on the wood furnace opens, a fan comes on and the fire comes to life to heat the water. It runs just like a FHW boiler, but with wood. )

Our company has put about ten of these systems in. You will have excess heat. All of the systems we put in do shut down when everything is satisfied, however we found that having a hot water fan coil in a garage worked pretty good. The heat in the boiler won't shut down fast enough to prevent the water from getting too hot.

Just our experience.

murph

SPIKER · Nov 29, 2004

Ive been looking at building my own, as I ahve access to everything needed including the Stailness Steel and shop presses benders cuters and tig machines. I was looking at different designs for years, and was thinking best ones recogmend using a hot water storage tank, which the cool tank water is heated by flowing through the boiler and the tank gets nice & how, the boiler shuts down nearly completely (or burns out) but there si a large suply of very hot water to use for hrs to come, once a day fireing for many applications depending on tank size, and how much wood is put in... TARM units suggest this. and no smoky yuck outside all winter long as the other types are smoldering after shutting down to a slow burn.

MarkM /forums/images/graemlins/shocked.gif

EdK · Dec 14, 2004

( TARM units suggest this.)

And you'd do well to follow their suggestion. I researched them, visited two installations and am in the process of installing my own. It's hard to argue with running full bore at the highest efficiency thus burning out the full load, storing the heat, and letting the thermostat call upon the reserve in storage as needed.