How many kilowatts heating element ?

Discussion in 'General Electronics Chat' started by Externet, Apr 11, 2016.

  1. Externet

    Thread Starter AAC Fanatic!

    Nov 29, 2005
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    A natural gas house heating furnace is 90000 btu/hr; runs less than 20% (perhaps 10%) of the time on a normal winter to keep the house comfortable.

    What electric heating element power could the gas burner be replaced with ? No problem if turns on 80% of time to supply the same amount of heat.
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    If i remember correctly, 1 BTU is equal to energy needed to rise the temperature of 1 pound of water by 1°F. Sadly I couldn´t be bothered to translate such a silly unit into anything meaningful ;)
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    1 kW = 3412.142 BTU/hr
    Electric furnaces come in 10kw to 27kw on average. In about 7 models.
    I have one for my garage that has 5 element selections for heat.
    Max.
     
  4. #12

    Expert

    Nov 30, 2010
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    90,000 BTUs/Hr is 26370 watts.

    Do you feel like you got pounced on?:D

    (I assume you can do the math now that you have the conversion factor.)
    5KW might do the job, but a 10KW heater only costs $50 (and the 6 AWG wire to connect it)
    while a 5KW will run on 10 AWG
     
    Last edited: Apr 11, 2016
  5. Externet

    Thread Starter AAC Fanatic!

    Nov 29, 2005
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    Just uncomfortable with gas-fed appliances because of safety about leaks; pilot lights, flames... do not like that.

    The BTU/hr and KW equivalence seems like should be something else more understandable as KWhr. (KW/hr ¿? ) -- So much gas burning during 1 hour related to so much Kw on during 1 hour.
     
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  6. MaxHeadRoom

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    Mideast USA? I don't quite see a 5Kw cutting it.
    The minimum we use here is 20Kw.
    BTW, modern gas furnaces to not have pilot lights anymore, as a rule.
    You could try Geothermal heat pump for heating/cooling also.
    Max.
     
    Last edited: Apr 11, 2016
  7. Externet

    Thread Starter AAC Fanatic!

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    Correct. 20KW is closer to the 90000 BTU equivalent of 26KW. But the time the gas actually burns in the furnace is ~10% in one hour.

    Perhaps ~5KW 'burning' 80% of the time...
     
  8. Hypatia's Protege

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    Mar 1, 2015
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    All the same, I agree with the OP -- Natural/LP gas service is an explosion and/or fire waiting waiting to happen! Around here HO Ins runs at least 2X for any means of fuel fired heating (by comparison to electric) and better than 3X where gas service is installed (Point being 'underwriters' know their statistics!) -- Can we say 'intrinsically unsafe'? --- Moreover, at ≈ $0.11 Per kWh - electric heating is not as costly as the fuel suppliers would have us believe!

    Best regards
    HP:)
     
    Last edited: Apr 11, 2016
  9. #12

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    Nov 30, 2010
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    The humans will feel more comfortable if the heater runs softly most of the time, and you aren't wasting the power used for the fan motor. It converts to heat at the same efficiency.

    I have the same feeling about flammable fuels. Then again, people who don't understand electricity can be just as suspicious of electric heat. The difference is, a fault in a properly installed flammable gas system can sneak up on you in several ways. A fault in a properly installed electric system just makes it stop.:D

    ps, a kilowatt of heater means a kilowatt hour per hour.

    If you have any doubts, you can buy the 10KW heater and don't connect half of it. If all else fails, connect the other half.
     
  10. MaxHeadRoom

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    To put it in perspective, I happen to live in a city of over 600,000 and the home heating, including water heating, is predominantly natural gas, it is extremely rare to ever hear of explosion/fire due to gas related, if it happens, it is often due to someone doing something stupid such as laying a basement floor using highly flammable adhesives etc.
    I consulted with my son-in-law who is a Fireman of 20+ yrs and he bears out the statistics that gas is not a principle cause of fires by any stretch.
    But due to the cost of Hydro electricity becoming more cost effective, there is now a trend to electric heating, after all we do have 15 hydro electric generating stations here. It should almost be free!.
    Max.
     
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  11. wayneh

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    Sep 9, 2010
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    My electric rate is rarely above $0.03/kWh (I have a real-time pricing plan). But even so, gas is still quite a bit cheaper. I don't consider it anymore a risk than electricity, so it's all about cost.
     
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  12. Externet

    Thread Starter AAC Fanatic!

    Nov 29, 2005
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    To run it 'softly' I was planning to run 230V heating elements I have on 120V. Will not get red-hot. Even can try electric range 'burning surface coils' which I have a bunch too. Or in series !

    See no mystery to it. As many as need to achieve the heat, properly placed/secured instead in the gas burner cavity and underpowered. Those coils are somewhere about 2KW at 230 V. To get rid of the gas paranoia. Clothes dryers have modular heating assemblies that can be adapted too.

    Also, the gas bill I have been paying is inflated with 'Service charge' , 'delivery charge' , taxes for this and for that. A detail in the bill shows ~$5 for metered gas consumption that ends in $40 ! with the added surcharges. Not just.

    Will let know how the surgery ends...
     
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  13. Hypatia's Protege

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    Mar 1, 2015
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    What can I say? A veteran firefighter's observation is clearly a quality measure!:) -- but then, by the same token, so are the findings of (insurance) actuaries... - Thus it seems said risk varies with locale (i.e. by installer, operator, etc...)
    For my part, sufficient hazards exist sans addition of those attending the piping of a flammable gas into my buildings!:eek: even did the alternative come at a multiple of the cost!

    For all that, I'd feel much better about gaseous heating fuels were the facilities equipped with external 'smart valves' designed to interrupt service upon detection of fuel contamination of indoor air and/or (if possible) 'pressure fluctuation signatures' indicative of leakage...

    Very best regards
    HP:)

    PS -- Yeah! I know! -- I'm the idgit who uses propane as a refrigerant:oops: -- Bang goes another window in my 'house of glass':eek::eek::eek::p:D
     
    Last edited: Apr 11, 2016
  14. Hypatia's Protege

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    That's an excellent rate!:):):)-- We seldom see less than $.098/kWh hereabouts (Xcel Energy) and that's considered 'bargain basement'!

    Would that be some manner of 'load management' arrangement?

    Best regards
    HP:)
     
    Last edited: Apr 11, 2016
  15. #12

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    Nov 30, 2010
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    Please measure the actual wattage or current or something. The math says half the voltage is a 4th of the power but these heaters change resistance according to temperature. I just don't know how much. There is also the fact that air flow keeps them cooler than one might expect.
     
  16. crutschow

    Expert

    Mar 14, 2008
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    Radiant electric heat, such as in a ceiling, tends to be efficient since it directly warms the objects (including the live ones) in the room, and only indirectly the air or the walls. Thus you can be comfortable at a lower air temperature then with a heater than warms the air.
     
  17. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Ha Ha HA Huh? Afraid of gas so you're going to cobble together a homemade electric furnace conversion out of old electric stove burners and maybe some dryer parts! :confused:

    MaybeI should have you meet up with an older buddy of mine who's house burned down due to electrical problems so he decided that the best thing to do with his new house was to toss the propane system and never look back. :rolleyes: :confused:

    On the more serious side of electric heat I would recommend baseboard heaters over a DIY furnace conversion and on top of that not go under 50% of the gas units BTU rating, ~15 KW, due to the likelihood of having horrible recovery times should the house ever cool off.
    Reason being my neighbors have all electric heat in their house and it sized to run near continuously when its real cold out which means that if they want t jump it up from 60 F to 70F for a family get together on a weekend they have to turn up the heat 3 - 4 days ahead of time to get there.:(
     
  18. ronv

    AAC Fanatic!

    Nov 12, 2008
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    I want some of that 3 cent per Kw Hr electricity.
    Better add your rate to your math calculations.
     
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  19. wayneh

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    Sep 9, 2010
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    Partly, but mostly because I have a semi-smart (logging) meter and hourly pricing. Most of the load management is by me, by time shifting things like the dishwasher and also banking by, for instance, cooling the house at night when the rate is low and coasting during the day. We also allow the power company to turn off our A/C compressor if they want, when the rate exceeds $0.14. That rarely happens but it's fine with me.
     
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  20. MrAl

    Well-Known Member

    Jun 17, 2014
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    Hi,

    For this and your previous post before that one...

    The difference in units is due to it being either a rate or just a set quantity. But time is always present so sometimes we dont have to mention time. A 10kw load that runs continuously is operating in time even though we dont mention that in the "10kw" itself.

    Time does get involved when the device does not run continuously however because then we have to consider the total energy, or the energy averaged over some time period.
    If we have a 40kw heater that runs 25 percent of the time then the total energy output is the same as a 10kw heater that runs for 100 percent of the time (continuously non stop). The only thing you have to watch out for is the original rating may be taking into account the worst case heating requirements. If the 40kw heater normally runs at 25 percent duty cycle, it may be that the original designer chose that rating because it was known that in that particular geographical location the temperature could occasionally drop much lower than the norm, and that 40kw would be required for rare but still possible weather conditions. Substituting a 10kw device may work most of the time, but may fail short during those extreme weather condition times. So some care has to go into choosing what size to install, and maybe a second one for those possible extreme times.

    Another consideration is the local/global distribution of the energy. We dont want all the heat in one location in the house, we want it distributed evenly so that all areas can get the heat they need. This may mean also taking into account the insulation properties of each room especially in older homes that have insulation in some walls and none or less in others. Cost considerations may make it worthwhile to add insulation in some areas.
     
    Last edited: Apr 12, 2016
  21. Hypatia's Protege

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    But isn't that when you'd need it most (assuming cost follows demand)? --- FWIW I could improve the rate for my residence building was I to permit the 'POCO' to 'fiddle' with power to my hot water boilers -- 'Tho there's something a bit too 'Orwellian' in that for my taste... --- My major 'gripe' is with their assessment of reactive power 'consumption' (do note the quotes) Re: my 3-θ (so-called 'industrial' service) though as long as usage remains in excess of the 5000 kWh/Mo 'wholesale threshold' it 'balances out' -- even so - until recently it was illegal to bill for 'VARs'...:mad: They know what their doing too - They seem to know it's not quite worth my while setting up an 'intelligent' power factor compensator -- Sly little gits!!!:mad::rolleyes:

    Well hey! -- Kudos on your arrangement! -- Seems you're getting a better deal than could be hoped for with a private wind farm?:cool:

    Best regards
    HP:):):)
     
    Last edited: Nov 21, 2016
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