Original message
| siestavista
 |  "furnace deregulation"
, posted Tue 7 Oct 17:43  
what is the oriface size or bit size to deregulate a furnace in the altitude of 4,500' with an input rating of 75,000 btu's?
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Replies:
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| Silvertop
| "Re(1):furnace deregulation" , posted Wed 8 Oct 07:21
75,000 btu's at sea level (14.7 psig) or 4,500' (12.5 psig)
When you alter the manuf operating range (bit size) of a unit you are asking for a big "BANG". If I understand you correctly, you want to get more heat out of the unit. There are a lot of safety issues involved here....heat chamber stress, air volicity and gas pressure....you may need to bite the bullet and purchase a larger unit
One step at a time
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| | siestavista
| "Re(2):furnace deregulation" , posted Wed 8 Oct 12:52
this is a modifided sears model. the unit is overfireing. the gas valve has been replaced and a standing pilot replaces the old spark ignighter. It has a 42 oriface now. the natural gas specific gravity here i image to be on the safe side would be 1000btu's at 4500' to 4600' i know it has not been deregulated. so, at .80 x 75,000 = 60,000. if you look on the chart, and i'm guessing, would be a 38 judging from the overfire.
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