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  1. #1
    DIY Member idoc4u's Avatar
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    Question 2 electrical questions

    Hi,

    I have 2 separate questions to ask, if you guys have some input, I'd appreciate the thoughts.

    1. If on a 15A breaker I have 3 - 100W lights + 12 - 65W lights + 1 water softener tranformer on the same circuit, this equals 1080W being used if they are all on at the same time not including the softener. The softener uses I believe .02 kW/h. While you should not exceed 80% of the 15A circuit (1440W) and although I don't know exactly how much draw the softener has but it seems like it would be very little, would it be a problem for any reason to have 15 fixture + the softener on the same circuit as long as the 1440W (80% rule) is not violated?

    2. Does anyone know the maximum ft sq covered by indoor electrical fireplaces and do they require a dedicated 20A circuit like electric base board heat? The big box stores sell units that cover 400 sq ft. and use 400Watts, from what I recall. The blowers seem rather weak, however. I'm considering gas instead, but thought I'd ask.

    Thanks for your input.

  2. #2
    Electrical Contractor Jim Port's Avatar
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    For general use circuits like you describe there is no 80% rule. It is a good design idea tho.

    Can't really help on the fireplace without knowing how many watts it draws.

  3. #3
    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by idoc4u View Post
    Does anyone know the maximum ft sq covered by indoor electrical fireplaces and do they require a dedicated 20A circuit like electric base board heat? The big box stores sell units that cover 400 sq ft. and use 400Watts, from what I recall. The blowers seem rather weak, however. I'm considering gas instead, but thought I'd ask.
    1 watt per sq. ft. sounds a bit light. In-floor electrical heating is usually 12 to 15, and a typical space space heater draws over 1000 watts. But as to gas versus electricity: Electric heat is 100% efficient (no $$ floating out the chimney) and never explodes.

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    Plumber jimbo's Avatar
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    Start with 10 watts per square foot on electric heaters, down to 30║. Add for lots of glass, poor insulation. X2 for Zero degrees, X3 for minus 30║.

    A hair dryer uses 1200 watts, so if some mutt in hd thinks that 400 watts will heat 400 square feet......good luck.

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    DIY Member Lightwave's Avatar
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    There's no such thing as a rule of thumb for heater sizing. You must do a load calculation to estimate how much power you'll need to heat a given room.

    Heating requirements vary hugely depending on room construction characteristics in addition to square footage. For example, in the same house, I have a 120sq/ft room that needs nearly 7,000btu (2kw electric) to heat and a 260 sq/ft room that needs only 4,500btu (1.3kw). The difference is all in the insulation, glass area, orientation, and ceiling height. There's no way to go from square footage alone to heater size--you have to do a proper Manual J load calculation to take into account construction in addition to volume.

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    Moderator & Master Plumber hj's Avatar
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    400 watts is less than two red infrared heat lamp bulbs. If the room was tightly sealed and insulated it MIGHT warm it up a little bit, eventually. But, a toaser oven might do just as good, or better, for a lot less money. Watch your television set. I believe the Amish are "giving their fireplaces away", just pay shipping and handling.
    Last edited by hj; 06-30-2010 at 06:30 AM.

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    Plumber jimbo's Avatar
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    Quote Originally Posted by hj View Post
    . I believe the Amish are "giving their fireplaces away", just pay shipping and handling.
    The rip off is a little different than that......the fireplace is free...you have to buy the "handcrafted cabinet" which sets you back a bundle.

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    DIY Junior Member IAMIR's Avatar
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    You are correct in saying rating a CB at 80%. NEC Sec. 384-16(c). You should not exceed 12 amps for a 15a breaker or 1440 watts. As an Electrical Estimator/Project Manager we run into this often on desighn build projects. The local jurisdictions will often look a load calculations in determining approval of permit drawings.

    The heater thing I am not familiar with so I will plead ignorance.

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