Want to make sure my calculations are right

[hotblueelectric]

Customer is building a 238 sq foot room with a bathroom, and wants to install (2) tankless water heaters. Thats it, lights, plugs, water heaters and window unit a/c /heat pump. He wants separate temperature for the sink than the shower. I tried using Mike Holts residential calculator which does not have provision for the tankless water heaters, and come up with around 149 amp total load. I think there may be a glitch in the version 2010H, or maybe because I am inputting the w/h loads at the bottom under other loads.
Any ways ran the calculation myself and just wanted to make sure I am OK.

lighting load 714 VA
w/h loads 31200
heat pump a/c 4800

total load 36714

1st 10000
26714 x .40 10685.6

total 20685.6 /240 = 86.19

Total Load 86.19

This look OK

 

[chris kennedy]

If your adding this to an existing service, you need to figure new and existing loads as per 220.83(B).

 

[gndrod]

Customer is building a 238 sq foot room with a bathroom, and wants to install (2) tankless water heaters. Thats it, lights, plugs, water heaters and window unit a/c /heat pump.

heat pump a/c 4800

This look OK

As Chris K mentions, [220.83(B)] combines existing and new load Demand factoring. Note this includes 100% of the larger of connected heat or A/C load, but not both.

Does the 4 ton window unit have heat strips installed? Check it out. This may reduce the heat pump optional deduction in favor of a lower total service capacity calculation.

 

[suemarkp]

Even if you're trying to calculate a feeder for just this equipment, the heap pump goes in at 100% -- you don't get to apply the 40% factor to the heating/cooling loads.

I'd be careful of using a storage water heater calculation value for a tankless because storage water heaters are continuous loads whereas the tankless wil not be. That spreadsheet cell will probably be treating the VA you enter as continuous.

 

[hotblueelectric]

I am coming off a separately metered shop with a 200 amp service, shop has only outlets and lights