# heat calc.



## JohnJ0906

Do you mean central heat? If so, see 220.51. ('05 NEC)


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## rll77

yes. heat pumps.


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## rll77

so do electric central units with heat pumps fall under the catagory of "electric space heating?" or am i missing something here ?


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## JohnJ0906

4 central air handler units, with 4 heat pumps, correct?
Do the AHUs have electric heat strips for backup?
This will probably ALL go on the service calc at 100%, unless the electric backup won't run at the same time as the heat pumps.
Also, I suspect on of those heat pumps will be your largest motor (add 25%)


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## rll77

not sure if they have heat strips. still gotta talk to the hvac guys . if they go at 100% thats gonna bump my service from 400 to 600. so its crucial i get this straight.


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## BryanMD

rll77 said:


> not sure if they have heat strips. still gotta talk to the hvac guys . if they go at 100% thats gonna bump my service from 400 to 600. so its crucial i get this straight.


They (almost) always do, the issue is how many watts each.
Definitely get cutsheets and have it in writing from the MC what he is using.


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## rll77

ok . im gonna find out tomorrow. I ,ve never built a 600 amp service for a residence before. anybody got any suggestions on the best way to go about it ?


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## BryanMD

rll77 said:


> ok . im gonna find out tomorrow. I ,ve never built a 600 amp service for a residence before. anybody got any suggestions on the best way to go about it ?


Call the poco.
They all do things differently.
And there may be issues (charges too) related to transformers and feeds;
akin to what they do for a small commercial customer.

With 400A (and especially with 600A) you are going to have multiple panels and probably in more than one location in the house. Check how they (and the AHJ) want that sort of thing handled and what sort of set up is best for YOU and THIS project.


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## rll77

well , i know im gonna have 200 upstairs and a 200 downstairs and probably a 400 in finished basement . what im figuring is how im gonna feed these panels.


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## rll77

outside service , ct s, troughs, etc. never designed one this size before.


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## a-bulb

I've done some pretty big resi services up to 1,200 amps. The most recent was a 800 amp, the poco in my area requires cts on anything over 320 amp. So I have a 800 amp ct cabinet, from there into a MDP with 200, 125,100 amp breakers that feed my panels 2-200 amp, 4-125 amp, 100 amp pool panel and 200amp to ATS from ATS to 200amp panel and then a 100 amp sub off that. can also skip out on the MDP and go with the tap rule and just have a ct cabinet with main and that will save some $...for the customer of course :whistling2: but like BryanMD said check with your poco and ahj and ask plenty of questions.


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## rll77

ok. let me try this again. im trying to decifer the code on calculating a heating load for a house. can anyone help ? i ve got four central units with heat pumps with back up heat. would thay all go at 100% load, or 65 %, or would this be considered space heating and i can derate it to 40 % since i have four or more? need help with this one .


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## Speedy Petey

rll, please don't start a new thread to continue the conversation. 
You are getting help here so keep it going.


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## JohnJ0906

OK, are you doing a standard calculation, or using an optional method?


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## idoelectric

Article 220.82 C 6. 2005 NEC


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## randomkiller

rll77 said:


> ok. let me try this again. im trying to decifer the code on calculating a heating load for a house. can anyone help ? i ve got four central units with heat pumps with back up heat. would thay all go at 100% load, or 65 %, or would this be considered space heating and i can derate it to 40 % since i have four or more? need help with this one .


 
Heat pumps used as a primary source aren't space heaters. On the coldest days they will all be on together running fulltime.


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