piping for hot water panels

[andyonu]

hi-newbie here-- i've done a bunch of research and I'm working on designing my closed loop solar hot water preheating system for a 6-unit apartment bldg.  I'm thinking about running the pipes from the roof down an old chimney that also is the flue for the boiler.  Advantage is I could capture some extra heat from the boiler flue gases.  disadvantage is that flue gases aren't so nice to copper?  any ideas?  pipe coatings?  fireproof insulation? Even if I can't capture any waste heat, the old chimney is still the best place for the pipe run.  

Also, I got a bunch of big old solar "hot air" collectors for free and I'm looking at the best way to plumb the boxes with piping so i can use them for heating water instead of air.  Anyone using old car/truck radiators inside a collector for heating water?  Any good links on the best way to design the piping for the collector? I'm thinking of soldering copper flashing to the copper tubes inside the box for more surface area facing the sun.

thanks!

andy o

[Capt Slog]

I know the idea of trying to extract heat from the flue gases sounds tempting, but I would say don't do it.

You rightly say that it will attack your tubing, but there is a more important factor.  The flue gases obviously go up the chimney because they are hot, cooling them down could affect the flow.  You stand a chance of causing carbon monoxide poisoning.

[Bruce S]

Capt;

  AMEN to that!!

Andy, one thing does come to mind when talking about the chimney, our codes say you must have a liner in there.

Ours is double walled steel; one thing if you have this would be to wind the plumbing down around the outside of the double walled lining . You would need to check code for this , it may not be allowed due to safety reason as Capt pointed out.

This would give you a little extra added heat, or at least help to maintain it's current temp while mvoing to other areas.

Also , you'll want to be careful when using old radiators, they used to be sealed with real lead solder, and some of the newer ones have internal plastic that was used for transmission cooling. Too hot and it'll be all over:-(

Hopes this helps a little

Bruce S

[wooferhound]

As I understand it . . .

The chimney parts need to be at 500 degrees or more or too much Creosote will condense onto the cooler parts, like the tubing you want to run. It would be accumulating creosote faster and it would be almost impossible to to clean properly.

[andyonu]

thanks--the building is about 120 yrs old.  the chimney is a huge old external brick thing, but past 100 yrs is has only been used as a flue for gas boiler-no wood crud and  no black creosote in there.  A 7" galvanized flue pipe from the boiler and hw heater is patched into the brick, but then it is just a huge opening.  At this point i'm just thinking of using it as a chase for the piping, but I'll still have to figure out how to protect and insulate the copper pipes.  I'm thinking of embedding them inside a 4" galvanized flue pipe then stuffing those with fiberglass insulation.  I can cut another opening in the brick below the boiler flue and seal it back up to prevent any CO issues.

andy o

[andyonu]

Thanks for the radiator cautions.  But if its a closed loop system, a little lead leaching wouldn't be a problem would it? just antifreeze in there, not potable water.

Do you know what type of pressure or temp radiators could handle?  I read somewhere most radiator caps are designed to vent at about 13 psi. I fear that's not enough.

thanks for your thoughts/ideas

andy o