Lennox International Inc G24-200 installation instructions Setting blower CFM

Setting blower CFM

Note − Turn electrical power off when adjusting mo- tor pulley. Blower RPM adjustment is accomplished by changing the motor pulley opening. Loosen Allen screw and turn pulley clockwise to increase RPM or turn coun- terclockwise to decrease. Re-tighten Allen screw. (See Blower motor/drive installation section for the pulley alignment and belt tensioning method.)

1 − Enter table 13 at design CFM and total external static pressure. (Design total external static pressure equals the sum of all pressure drops across all acces- sories which are installed external to furnace and all ductwork/accessories. See table 14 for external filter box with filters pressure drops, C17 coil pressure drops and EMD17M economizer pressure drops.)

2 − The table yields a value for design BHP and RPM.

3 − Select drive kit so that motor maximum BHP (as shown in table 15) exceeds the value from table13.

4 − Run the blowers and measure the actual blower shaft RPM and total external static pressure.

5 − Adjust RPM to the value in table13 which will result in the design CFM. From design CFM and actual Total Exter- nal Static Pressure reading, Table 13 gives required BHP. This value should still be lower than the maximum BHP delivered by the motor as shown in table 15.

6 − As a final check, measure the motor’s current draw and compare it to the motor’s nameplate service factor amps rating (SFA). If the current draw is not less than or equal to the SFA rating, reduce the motor’s load until it is.

TABLE 13

CFM vs TOTAL EXTERNAL STATIC PRESSURE

								Total External Static Pressure − in. w.g. (Pa)
Air
	.10 (25)		.20 (50)		.30 (75)		.40 (100)		.50 (125)		.60 (150)		.70 (175)		.80 (200)		.90 (225)		1.00 (250)		1.10 (275)
Volume
cfm	RPM BHP		RPM BHP		RPM BHP		RPM BHP		RPM BHP		RPM BHP		RPM BHP		RPM BHP		RPM BHP		RPM BHP		RPM BHP
(L/s)
		(kW)		(kW)		(kW)		(kW)		(kW)		(kW)		(kW)		(kW)		(kW)		(kW)		(kW)
2400	- - - -		- - - -		535	0.30	600	0.35	665	0.45	720	0.55	755	0.65	825	0.75	875	0.85	920	0.95	965	1.05
(1135)						(0.22)		(0.26)		(0.34)		(0.41)		(0.48)		(0.56)		(0.63)		(0.71)		(0.78)
2600	- - - -		- - - -		545	0.35	610	0.40	670	0.50	725	0.60	780	0.70	830	0.80	875	0.90	920	1.00	965	1.10
(1225)						(0.26)		(0.30)		(0.37)		(0.45)		(0.52)		(0.60)		(0.67)		(0.75)		(0.82)
2800	- - - -		- - - -		560	0.40	620	0.45	680	0.55	735	1.05	785	0.75	835	0.85	880	0.95	925	1.05	965	1.15
(1320)						(0.30)		(0.34)		(0.41)		(0.48)		(0.56)		(0.63)		(0.71)		(0.78)		(0.86)
3000	- - - -		- - - -		570	0.45	630	0.55	690	0.60	740	0.70	790	0.90	840	0.90	865	1.00	930	1.15	970	1.25
(1415)						(0.34)		(0.41)		(0.45)		(0.52)		(0.60)		(0.67)		(0.75)		(0.86)		(0.93)
3200	- - - -		- - - -		585	0.50	640	0.85	685	0.70	750	0.80	800	0.90	845	1.00	890	1.10	935	1.20	975	1.35
(1510)						(0.37)		(0.45)		(0.52)		(0.60)		(0.67)		(0.75)		(0.82)		(0.90)		(1.34)
3400	- - - -		535	0.50	595	0.55	655	0.65	710	0.75	760	0.85	805	0.95	855	1.05	895	1.20	940	1.30	- - - -
(1605)				(0.37)		(0.41)		(0.48)		(0.56)		(0.63)		(0.71)		(0.78)		(0.90)		(0.97)
3600	- - - -		550	0.55	610	0.65	665	0.75	720	0.85	770	0.95	815	1.05	860	1.15	905	1.25	945	1.40	- - - -
(1700)				(0.41)		(0.48)		(0.56)		(0.63)		(0.71)		(0.78)		(0.86)		(0.93)		(1.04)
3800	- - - -		570	0.60	625	0.70	680	0.80	730	0.90	780	1.05	825	1.15	870	1.25	910	1.35	955	1.50	- - - -
(1795)				(0.45)		(0.52)		(0.60)		(0.67)		(0.78)		(0.86)		(0.93)		(1.01)		(1.12)
4000	- - - -		585	0.70	645	0.80	695	0.90	745	1.00	790	1.10	835	1.25	880	1.35	920	1.45	960	1.60	- - - -
(1890)				(0.52)		(0.60)		(0.67)		(0.75)		(0.82)		(0.93)		(1.01)		(1.08)		(1.19)
4200	550	0.70	605	0.80	660	0.90	710	1.00	760	1.10	805	1.25	850	1.35	890	1.45	930	1.60	970	1.70	- - - -
(1980)		(0.52)		(0.60)		(0.67)		(0.75)		(0.82)		(0.93)		(1.01)		(1.08)		(1.19)		(1.27)
4400	570	0.80	625	0.90	675	1.00	725	1.10	770	1.20	815	1.35	860	1.45	900	1.60	940	1.70	- - - -		- - - -
(2075)		(0.60)		(0.67)		(0.75)		(0.82)		(0.90)		(1.01)		(1.08)		(1.19)		(1.27)
4600	590	0.90	645	1.00	695	1.10	740	1.25	785	1.35	830	1.45	870	1.60	915	1.75	950	1.85	- - - -		- - - -
(2170)		(0.67)		(0.75)		(0.82)		(0.93)		(1.01)		(1.08)		(1.19)		(1.31)		(1.38)
4800	610	1.00	660	1.10	710	1.25	755	1.35	800	1.45	845	1.60	885	1.75	925	1.85	965	2.00	- - - -		- - - -
(2265)		(0.75)		(0.82)		(0.93)		(1.01)		(1.08)		(1.19)		(1.31)		(1.38)		(1.49)
5000	630	1.10	680	1.25	730	1.35	775	1.50	815	1.60	860	1.75	900	1.90	940	2.00	975	2.15	- - - -		- - - -
(2360)		(0.82)		(0.93)		(1.01)		(1.12)		(1.19)		(1.31)		(1.42)		(1.49)		(1.60)

NOTE − All air data is measured external to furnace using rear return air opening without air filters in place.

Bold text indicates 2 H.P. (1.5 kW) drive kits.

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