Preheating AUF/AOF

Has anyone tried preheating there AOF/AUF by putting a larger diameter pipe around their smoke stack. So for example i run an 8 inch stack, i was thinking of trying 10 inch pipe around it with a Tee at the bottom that could be reduced down to hook to my blowers. I run 800 degree stack temps but at the rate of flow my blowers use im not sure if it would get too hot. I also thought if not go all the way through the roof with the outer pipe i could add or subtract pipe lengths to adjust the temp. I wouldnt think i would want to run temps of more that 150 degrees but i think any would help. Thanks Jeff

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Originally Posted by Wanabe1972

Has anyone tried preheating there AOF/AUF by putting a larger diameter pipe around their smoke stack. So for example i run an 8 inch stack, i was thinking of trying 10 inch pipe around it with a Tee at the bottom that could be reduced down to hook to my blowers. I run 800 degree stack temps but at the rate of flow my blowers use im not sure if it would get too hot. I also thought if not go all the way through the roof with the outer pipe i could add or subtract pipe lengths to adjust the temp. I wouldnt think i would want to run temps of more that 150 degrees but i think any would help. Thanks Jeff

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go find my pictures and take a look

It looks like your pulling from the piggyback or steam away is that what you do or is this the wrong picture?

I have seen where some people have run steel pipe under the flue pan or in the transition area from the flue pan to the stack, basically making use of the hot air that is going up the stack. I think the idea is to have your blower pushing the hot air through the system from the start rather than having the blower handling the hot/super heated air.

Yes sir, I have a 2 x 6 with a 10 inch over an 8 inch stack. AOF & AUF. I think it works great! Truly believe it saves me fire wood. Would do it again.

It would definitely help but I'd have the blowers draw in cold air, push it through the space between the 8" and the 10" stack pipes (I'd go bigger to say 12" for the outer) and to the AOF/AUF nozzles.

The commercial high efficiency wood units (like our Force 5) draw in cold air and pipe it around the fire box to the nozzles but your idea is definitely something worth trying!

I'm going to try something but I'm not sure what yet. I think pushing the air is the proper way to do it but I have pulled hot air 160 to 180 degree through a squirrel cage blower for years without an issue.

Preheating will make a huge difference in fuel consumption. Increased our charge duration on the outside wood heater by feeding the blowers hot air from a 10" around an 8" well casing. Nearly a 40% increase in efficiency.

I have sketched out running a tube inside the chimney and into an AOF and AUF.

This was before I put an exhaust fan for a garage to remove the truck exhaust onto my air under fire. The pressure is so high I don't need any AOF to maximize the burn wood lasts longer next to no ash and stack color is clear 30-50 seconds after a charge of wood.

Pulling in ambient air will make the fans last longer. My motors need lubrication every 4 months when in hot air. annually for the one in the warm room air.

I am currently building a air preheater for my AOF on my 2x6 raised flue. It will be very similar to what was done here: http://mapletrader.com/community/sho...eated-AOF-mods.

The user that constructed this said it has held up well over the 2 years use so far. I'll post pics of mine when I get it put together.