#1  
Old 06-01-2009, 12:23 AM
Serf
 
Join Date: Apr 2009
Location: Yokohama, Japan
Posts: 3
Default Using Oven Exhaust heat for heating slab?

Greetings from Yokohama. I'm planning my restaurant design (December '09 open) and have been wondering about harvesting the exhaust heat from the oven to heat my outdoor veranda concrete slab!! Has anyone tried reclaiming duct heat? I'm thinking hydronic floor heating technology here. Am I mad?!
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  #2  
Old 06-03-2009, 04:38 AM
Il Pizzaiolo
 
Join Date: Mar 2009
Location: USA
Posts: 1,436
Default Re: Using Oven Exhaust heat for heating slab?

i have no experience with it, But im sure it could be done and is a GREAT idea... Maybe you could run piping thru the oven to heat water that wouuld run under the floor (in piping) as well.. You might need a holding tank to help control temperature properly.

Good luck
Mark
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Old 06-03-2009, 04:58 AM
Serf
 
Join Date: Apr 2009
Location: Yokohama, Japan
Posts: 3
Default Re: Using Oven Exhaust heat for heating slab?

Thanks Mark. The holding tank I picked up a few months ago. A beauty stainless job. I was worried about messing with the thermal mass of the oven, and that's why I'm thinking exhaust duct... I'm thinking a coil that goes right around the duct for about a meter. That's a lot of exposure to the heat, and then it's straight into the tank and then off to the patio. In theory...
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Old 06-03-2009, 06:05 AM
Il Pizzaiolo
 
Join Date: Mar 2009
Location: USA
Posts: 1,436
Default Re: Using Oven Exhaust heat for heating slab?

my thought, would be place your coil around the outside of the oven, then insulate over it. If you are high volume you will be constantly burning a fire in the oven to hold temp and the water should heat fairly quickly (guessing) but will be insulated and will continue to gain heat for the holding tank even after the oven is shut down. The only downfall i see with your idea is your only heating when your burning.. Other than that i think either way could work very well...

tell me what you think..

mark
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  #5  
Old 06-03-2009, 07:22 AM
Il Pizzaiolo
 
Join Date: Nov 2006
Location: San Antonio
Posts: 1,719
Default Re: Using Oven Exhaust heat for heating slab?

Hi Iggy!

I tend to think "around the chimney" makes more sense. However, it should be noted that chimneys get seriously hot (especially uninsulated stone wrapped chimneys) and that you may encounter boiling (depending on your flow rate) and corrosion issues. Hot water exacerbates corrosion and if you mix metals you will also have to deal with galvanic corrosion. All present design problems whereever you put the coils. Boiling could be seriously dangerous - especially if you have a closed (potentially pressurized system). Your storage tank should probably be vented to make sure it doesn't explode or rupture a connection in your plumbing.

IF you run your oven purely as a pizza oven it might not make much difference where you put the coils but if you plan to use it as a bread oven or for baking you would not want the water in the coil cooling your oven.

Good luck!
Jay
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  #6  
Old 06-03-2009, 11:49 AM
Master Builder
 
Join Date: Mar 2008
Location: Washington State USA
Posts: 780
Default Re: Using Oven Exhaust heat for heating slab?

Iggy, Great idea and to add to what Jay contributed: I would make the system open with a well vented expansion/storage tank. You will probably have some concern as well that with the slab that is to be heated lower than the heating coils in an open system the storage/expansion tank will need to be at the same height as the heating coils. One could design it so the expansion of the heated water drives/pumps the system eliminating pumps (convection driven). I would think in order to have a fail safe system one would want to remove any possibility of pump failure causing dry hot pipes and consequent live steam when water encounters them. Then too you might consider two loops: one convection to heat the storage tank and the other to take the heated water to the slab so that you could adjust the temp in the slab. No need heating the slab on a hot summer day :-)

Many years ago I stayed in a two story home in the Lake District in England where a set of pipes behind the cast iron fire back heated a radiator/storage tank in the bedroom directly upstairs. It worked by convection of the hot water and I was told had been working successfully for over a hundred years.

Bests,
Wiley
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  #7  
Old 06-03-2009, 03:18 PM
Il Pizzaiolo
 
Join Date: Nov 2006
Location: San Antonio
Posts: 1,719
Default Re: Using Oven Exhaust heat for heating slab?

Hi Wiley!

I was thinking about natural convection also just so it couldn't "fail" - at least for the circulation to the tank. The circulation through the slab should probably have a pump - if nothing else to allow temperature control. In a natural convection system you would tend to want to have the storage tank above the heating coil and that will require some thinking (at least for a free standing oven). In a restaurant there is likely to be an easier configuration! Glad you mentioned it!

And good luck, Iggy!
Jay
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  #8  
Old 07-05-2009, 11:59 PM
Serf
 
Join Date: Apr 2009
Location: Yokohama, Japan
Posts: 3
Default Re: Using Oven Exhaust heat for heating slab?

Thanks guys for the feedback. In consultation with a builder and research of current systems the expansion tank is a must as is the heat exchanger plan. That way we avoid the summer patio griddle effect. And we keep the metal pipe oxidization away from the closed line to the slab.
Wiley, that UK heating system is a real hangover from the Roman invasion you know!
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