Bard W24G3DA Installation Instructions Manual

Bard W24G3DA Installation Instructions Manual Manual pdf 30 page image

Manual 2100-631Page 30 of 5321. STANDARD ORIFICE SIZING ANDHIGH ALTITUDE DERATEThis furnace is shipped with fixed gas orifices for usewith Natural Gas and sized for 1000 BTU/cubic footgas. Make sure actual gas input does not exceed ratingplate input. You may need to change orifices to getcorrect gas input. Whether you do or not depends oninput, and your gas heat value at standard conditionsand elevation. Consult your local gas supplier for gasheat value and any special derating requirements. SeeSection 20 for more information.At higher altitudes, the density of the air is reduced.Therefore, for proper combustion, the quantity of gasburned in the furnace must also be reduced. Thisis called derating. This unit must be derated wheninstalled at altitudes greater than 6,000 feet abovesea level. A high altitude pressure switch must also beinstalled for operation above 6,000 feet. High altitudepressure switch kit number 8620-189 is designed forthis application.TABLE 7NATURAL GAS DERATE CAPACITIESFOR ALL MODELSW**G RatedInput Sea Level 1000 2000 3000 4000 5000 6000 7000 8000 9000 10,00041,00045,00040,50045,00039,20443,56037,90842,12036,61240,68035,64039,60034,99238,88034,18237,98033,69637,44033,04836,72032,64336,27032,07635,64061,00068,00060,75067,50058,80665,34056,86263,18054,91861,02053,46059,40052,48858,32051,27356,97050,54456,16049,57255,08048,96554,40548,11453,46075,00081,00075,00081,00072,60078,40870,20075,81667,80073,22466,00071,28064,80069,98463,30068,36462,40067,39261,20066,09660,45065,28659,40064,15290,000100,00090,000100,00087,12096,80084,24093,60081,36090,40079,20088,00077,76086,40075,96084,40074,88083,20073,44081,60072,54080,60071,28079,200113,000125,000112,500125,000108,900121,000105,300117,000101,700113,00099,000110,00097,200108,00094,950105,50093,600104,00091,800102,00090,675100,75089,10099,000It is the installer’s responsibility to see that thefurnace input rate is adjusted properly. Deratingmust be achieved by reducing the size of the mainburner orifices. Derating the furnace by adjusting themanifold pressure lower than the range specified inthe Section 19, “Manifold Pressure Adjustment” isconsidered to be an improper procedure.Above 6,000 feet elevation orifice changes arerequired, and capacity reductions are a function ofaltitude impact and orifice change. Pressure switchchange is required above 6,000 feet elevation. ForNatural Gas see the Altitude Table 7 below and theOrifice Tables 8 and 8A on following pages.