Help with load calculation

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BattleCat

Member
Location
NJ
I don't have that much experience with residential load calculations other than what I've done in school and licensing testing years ago :p

I have a few questions that I would greatly appreciate help with.

I am using the Load Calculator spreadsheet that can be found on Mike Holt's website. I don't see any entry boxes for some things, so I wonder if we just shouldn't include those things? Bathroom exhaust fans? Ceiling fans? Garage door openers? A small counter top microwave? I'm curious what appliances in a typical house should be listed?

The house in question is all natural gas, the only big electrical load is central air. So what do I count the air handler as? The air handlers are used for both forced hot air and central AC, but they are just gas furnaces so they don't use much power. The air handler entry in the load calculator is only for electric heat. So I wonder if I should just add whatever the air handler uses to the AC condensor? How would you go about that?

One other thing that I am curious about is if this calc automatically includes calculating the 25% of the largest motor to the load calculation? I don't see it listed anywhere on the spreadsheet.
 

Gregg Harris

Senior Member
Location
Virginia
Occupation
Electrical,HVAC, Technical Trainer
I don't have that much experience with residential load calculations other than what I've done in school and licensing testing years ago :p

I have a few questions that I would greatly appreciate help with.

I am using the Load Calculator spreadsheet that can be found on Mike Holt's website. I don't see any entry boxes for some things, so I wonder if we just shouldn't include those things? Bathroom exhaust fans? Ceiling fans? Garage door openers? A small counter top microwave? I'm curious what appliances in a typical house should be listed?

The house in question is all natural gas, the only big electrical load is central air. So what do I count the air handler as? The air handlers are used for both forced hot air and central AC, but they are just gas furnaces so they don't use much power. The air handler entry in the load calculator is only for electric heat. So I wonder if I should just add whatever the air handler uses to the AC condensor? How would you go about that?

One other thing that I am curious about is if this calc automaticallyincludes calculating the 25% of the largest motor to the load calculation? I don't see it listed anywhere on the spreadsheet.


Take a look at 422.12 depending on the gas furnace it could require 15,20, or 30 amp individual branch circuit
 

kingpb

Senior Member
Location
SE USA as far as you can go
Occupation
Engineer, Registered
This probably won't help you, but just keep in mind the NEC is based on minimum(s). If you are trying to cheapen your cost, then follow it to a tee. I guess if you were trying to do a load calc for a bunch of pop out residential homes it works, but personally, the NEC is to thin for my liking and if I was designing my own home or a custom home, I would be much more liberal with the loads and number of circuits. It is my belief that services are generally too small. But I am more old school, such as I would not mix lights and receptacles either.

Happy Thanksgiving!
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
You don't figure in ceiling fans and bath fans because they are included in the watts per sq, foot. The counter top microwave is figured in with the small appliance branch circuits at 1500 watts times 2.

There are places for microwave on the spreadsheet but I would only use that for a built in setup. Also bottom right has places for continuous motors and non-continuous motor. The 125% is in the continuous motor calc.
 

BattleCat

Member
Location
NJ
You don't figure in ceiling fans and bath fans because they are included in the watts per sq, foot. The counter top microwave is figured in with the small appliance branch circuits at 1500 watts times 2.
Gotcha! So I guess the garage door openers are already factored into the watts/sqft?

There are places for microwave on the spreadsheet but I would only use that for a built in setup. Also bottom right has places for continuous motors and non-continuous motor. The 125% is in the continuous motor calc.

So should I add one of the AC condensing units to the continuous motors so that it gets applied? I remember always doing an AC unit in a dwelling for the 25% largest motor load.

As far as the air handling units, just ignore them because they are gas and the AC condensing unit is already factored in?
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I would add the nameplate for the gas units-- usually around 13-16 amps and I would not add 125% to the A/C. I would add the garage door openers to the calc because they are permanent install and not moveable as the appliance on the counters.
 
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