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</o:shapelayout></xml><![endif]--></head><body bgcolor=white lang=EN-CA link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Dear Darren<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>First the cast iron grate is about right for the 4 kW (average, not peak) power you want. I have been trying to make a 4 kW stove that burned clean and the whole grate area is about 155 x 220 after discounting the parts that are hiding under shields. What matters is the volume of coal or wood burning at once. That sets the power level.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>I just want to confirm that the bleed hole takes hot fire gases from the top of the combustion area into the flue before they go down into the heat exchange, in other words like a GTZ 7.5 (now to be called a GIZ 7.5 after their name change).<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><br>***** Do people think this should this provide sufficient secondary air or should I put another similar secondary inlet in the front of the burner??? *****<br><br><span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Actually I can’t see it clearly. How big is it?<o:p></o:p></span></p><p class=MsoNormal><br><span style='color:#1F497D'>></span>With this 'door' wide open the bleed hole is 5cm x 10cm<br><br><span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>That is easily large enough.<o:p></o:p></span></p><p class=MsoNormal><br><span style='color:#1F497D'>></span>My friend had a grate from an old coal stove that appeared to be a suitable size and we intend to use - from memory this grate is approx 15cm x 20cm. Thinking of having the 15cm side in front of the 10cm throat through into the combustion area.<br><br><span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>The whole grate does not need to be under the combusting zone. About ½ is correct to give a crossdraft through the bottom of the fuel in the hopper.<o:p></o:p></span></p><p class=MsoNormal><br><br><o:p></o:p></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>>></span><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Based on the hopper size, and presuming you have about 4 metres of chimney, </span><o:p></o:p></p><p class=MsoNormal><br><span style='color:#1F497D'>></span>If the chimney was shorter what would be the effect? <span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Power is related to the draft, taller chimney means more draft means more power. You can choke it of course with a damper.<o:p></o:p></span></p><p class=MsoNormal><br><span style='color:#1F497D'>></span>The primary air hole should be 30x120mm? With a valve so its adjustable?<br><br><span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Yes. If you are quite short, it will be obvious in the thermal efficiency number because too much excess air (secondary air oversupplied) will give a cool burn and a high Stack EA (= low efficiency).<o:p></o:p></span></p><p class=MsoNormal><br><span style='color:#1F497D'>></span>Shes got plenty experience making air tight doors<br><br><o:p></o:p></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'> </span><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Good!</span><span style='font-size:11.0pt;font-family:"Calibri","sans-serif"'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>The Hopper size:<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>></span>Am I better reducing dimensions more than we are talking here?<br><span style='color:#1F497D'>></span>Throat?<br><span style='color:#1F497D'>></span>Hopper area? <span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>You can easily slim the hopper by dropping clay slabs inside it to narrow it. Ditto with the grate actually.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>></span>- or do I not want the entire floor of the hopper to also be a grate?<br><br><span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Yes, almost. As the air is not rising into the hopper other than enough to get over to the combustion area, making it too small or too much tucked under the combustion area will limit the power, maybe to the point of it not working well. In your drawing you have the grate nicely angled but stopping before it got under the combustion area. With the angled grate extending from under the hopper (except perhaps the bit at the very front) to the back of the combustion area (the flame runs vertically from there) you can make a crossdraft fire that is adjustable across a pretty good heat range.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><br>Perhaps you can make a good drawing in cross section of what you have now.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Regards<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Crispin<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>