I am looking to install all new kitchen appliances and wanted to see if my current service would be sufficient. I am trying to calculate the service load using Article 220 of the NEC 2014 and I am trying to figure out what my AC/Heating Load would be. I have a Gas Furnace and AC unit which the same blower motor.

My Furnace Unit is the G60UHV−36B−090. The datasheet can be found here: https://tech.lennoxintl.com/C03e7o14l/VIu12Ch2uV/ehb_g60uhv_0812.pdf

My AC Unit is this HS19-411: https://tech.lennoxintl.com/C03e7o14l/VIu12Ch2uV/ehb_hs19_0894.pdf

Blower Motor Calculation: Page 7 of the Furnace datasheet says the blower motor output is 1/2 hp. It also says that the furnace runs of 120V-60Hz-1 phase and no more than 12 amps. Table 430.248 says the full load current for a 1/2 hp motor is 9.8A. Since my motor is running off of 120 V, this means the blower motor load is taken as 9.8A * 120V = 1176W?

AC Unit Calculation My AC unit is running off 240V (30A double pole breaker). Page 6 of the AC Unit datasheet shows the Electrical Data for the unit. Now this is were things get a bit confusing. The table lists three different currents for the AC unit (HS19-411), Rated load amps for the compressor, full load amps for the condenser, and then a minimum circuit ampacity. Which one of these is relevant for the purposes of a load calculation?

Total AC/Heat Load Now since the AC and Heat won't be running at the same time I would need to take the largest of the two loads and use that in the total calculation. Apart from the blower motor running, I don't think the furnace uses much electricity at all since it is a gas furnace. Therefore, I would use the AC Unit Load (240V * whatever current is relevant) plus the blower motor load and then that would be my AC/Heating load correct?

Thanks in advance for any help.

1 Answer 1


Use the MCA for the outdoor unit

Best I can tell, outdoor units are accounted for in load calculations using the condensing unit's nameplate Minimum Circuit Ampacity. This is listed at the bottom of the same table you found the compressor power specs in, but also includes other accessories, such as the condenser fan.

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