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56 | DE-RATING FOR ALTITUDE INSTALLATION
Appendix H - De-rating for altitude installation
When the appliance is installed at an altitude higher than 2000 ft, the fan speed must be set to the top of the available range in any case and a de-rating
of the input capacity must be considered in function of the altitude combined with the total length of the vent and combustion air pipe as reported in the
following table (input BTU/hr):
SSB 800 SA
Altitude (ft)
0-2000
3000
4000
5000
6000
7000
8000
9000
10000
SSB 1000 SA / 1000 TL
Altitude (ft)
0-2000
3000
4000
5000
6000
7000
8000
9000
10000
To calculate the de-rating of the input capacity follow this example:
We have an SSB 1000 SA boiler installed at 5400 ft with a 6" flue system. The equivalent length of the vent pipe installed is 55 ft.
The equivalent length of the air combustion pipe installed is 35 ft.
The total equivalent length of the flue system is 55+35 = 90 ft. The maximum equivalent length for this type of installation is (see IOM manual) 100 ft.
The % range is 90/100 = 90%. This value is within the 75% and 100%.
Now the correct de-rating value is given from the value of the fourth column (From 75% to 100%) of the SSB 1000 SA / 1000 TL table that crosses
the row with 6000 ft: 783520 BTU/hr.
6720866942 (2018/06) US
From 0% to 25%
From 25% to 50%
798000
732482
708185
683889
659592
635298
611001
586707
562408
From 0% to 25%
From 25% to 50%
1000000
917896
887450
857004
826557
796112
765665
735220
704773
From 50% to 75%
798000
798000
719768
707056
695893
683603
672021
660151
648144
636698
624272
613246
600397
589793
576523
566341
552648
542888
From 50% to 75%
1000000
1000000
901967
886035
872047
856645
842131
827256
812212
797866
782296
768478
752376
739087
722461
709701
692541
680310
From 75% to 100%
798000
694344
671312
648281
625250
602220
579187
556159
533126
From 75% to 100%
1000000
870105
841243
812383
783520
754661
725800
696939
668078
SSB
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