CO2 emissions and compact fluorescent bulbs (updated)

There’s something about the idea of global warming that seems to drive people of a certain mindset completely insane. You start seeing things like: “the planet’s not warming up!” “Okay, maybe it is warming, but humans couldn’t possibly be causing it.” “Fine. We are causing global warming, but we can’t do anything about it.” “What, we can? Well it’ll destroy our economy.” “You mean it won’t? Well, you must be French.”

And then you get guy’s like Andrew Longman whose argument runs something like, “I don’t believe in global warming, but you do. And congress’s ban on incandescent bulbs is going to put out more CO2 which in your mind means we’re baking the planet. Stupid liberals.” Then, after derisively stating that liberals are not hard headed quantitative types, proceeds to lay out an argument that is so stupid, a 12th grade physics class could take it apart.

Unfortunately, a 12th grade physics class isn’t here right now, so we’ll have to do it ourself.

Longman’s argument is that incandescent bulbs replace some portion of the normal heating used in a house. An NPR story told him that electric heat is more efficient than burning natural gas – in terms of CO2 emissions per unit of heat, therefore, by converting to CF bulbs we are using less electricity to heat our homes and more natural gas therefore, we are putting out more CO2 than if we used the original incandescents. He then proceeds to describe liberals as soft headed and laughs that their silly utopian dreams are undone by lack of an engineering mindset.

That’s a challenge that’s hard to resist. So let’s take this apart. First, Longman doesn’t realize that he’s comparing three different kinds of heating. He’s simplified to two: gas and electric. But let’s be quantitative and list all three:

  1. natural gas heaters
  2. electric resistive heaters
  3. heat pumps

Natural gas heaters burn natural gas, heating air that is then circulated around the house. Pretty simple idea. Relatively efficient.

Of course, very few people heat their homes with electric resistive heaters. This is the “emergency” or “auxiliary” heat setting on your heat pump. You run electricity through something resistive and generate heat. It’s a one to one conversion of heat for electricy. Every watt you put in, you get one watt of heat out. Run it for a length of time, and you can covert to watt-hours or BTUs. Now wait, I mentioned that you get electric resistive heaters by running electricity through a resistor – that’s a light bulb! Okay, we now know that light bulbs are electric resistive.

It’s very expensive to use electric resistive heat. So most people using electric heat use a heat pump. Think reverse air conditioner – you air condition the outside in winter extracting the heat and putting it into the house. A given heat pump, operating at a given temperature differential will have a specific coefficient of performance (CoP). Essentially, how much electricity does it take to extract a given amount of heat. Depending on circumstances, that CoP may be between 2 and 5. In other words, it takes 1 watt of electricity to extract between 2 and 5 watts of heat from the outdoors and move it inside. Hrm, now we’re starting to see how NPR got its numbers for pounds of CO2 created heating a house with electric vs natural gas.

But of course, Longman has challenged us to be quantitative and so we must preserve persevere. Let’s look at his example. Assume you have a house that contains 30, 100 watt bulbs that are always burning. In his example, a conversion to 20 watt compact fluorescents would mean that instead of getting 3000 watts of heat from the bulbs, you now get only 600 watts of heat from the bulbs and have to burn the equivalent of 2400 watts worth of natural gas. Using his soft, fuzzy, NPR numbers (that he’s misunderstood), Longman says that you emit less CO2 with the incandescents.

But he hasn’t really shown that. So let’s do the math. Basic numbers we’ll need:

  • CO2 emissions per unit of heat from natural gas
  • CO2 emissions per watt-hour of electricity
  • watt-hours consumed using our 30, 100 watt bulbs over a period of time

According to the Natural Gas Association, 1 billion (1,000,000,000) BTUs of heat from natural gas produces 117,000 pounds of CO2.

According to the Department of Energy, we produced 1.341 pounds of CO2 per kilowatt hour of energy generated in 2000. (Note, this is generated, some power is lost in transmission, so this is an upper lower bound for [CO2 generated by] power energy used in a home).

Now we’re getting somewhere. So 30 bulbs at 100 watts each, use 3000 watts of power or 72 kilowatt hours per day. That works out to 96.552 pounds of CO2 per day for heating your home with light bulbs.

What about natural gas? Well, we don’t have a CO2 pounds per kwh for natural gas, but since the CoP of a light bulb is 1.0, we have a conversion from electricity to heat. Our 72 kwh of electricity converted directly to heat turns out to be 245800 BTUs. Which turns out to generate 28.7586 pounds of CO2 if produced by natural gas. Of course, we haven’t replaced100% of our light bulb heat by switching to CF bulbs, only 80%. The other 20% is still [comparable to] electric resistive. So if we take 80% of 28.7586 and add 20% of 96.552, we get 42.311 pounds of CO2 generated by using 30, 20 watt CF bulbs.

Now, unless I’ve forgotten my basic math, 42.311 pounds is less than half of 96.552 pounds. So, I think that means that Longman was full of crap and is apparently a fuzzy headed conservative and not really a quantitative man at all.



Oh, so I forgot to look at summer when we’re trying to cool the house. Turns out that the difference is even greater. In the summer, all of the heat is waste heat – we don’t want it and we need to get it outside. Assuming we’ve got a high efficiency air conditioner, it takes about one watt-hour of power to remove five watts-hours of heat, i.e., let’s assume a CoP of 5.

In the summer, running Longman’s 30, 100 watt bulbs 24 hours a day still takes 72 kwh per day plus we’ll need to run the a/c for another 14.4 kwh per day. That gives us a total of 86.4 kwh creating at least 115.824 pounds of CO2.

If we assume that all of those bulbs are now 20 watt compact fluorescents, then we require 14.4 kwh for light, plus another 2.88 kwh for cooling. Total of 17.28 kwh per day for lighting and cooling the lighting. Those 17.28 kwh will create… 23.17 pounds of CO2. Or not surprisingly, one fifth the CO2, since the bulbs use one fifth the electricity.

Of course, not everyone is going to use 30, 100 watt bulbs for lighting 24/7, but the relative proportions stay the same.


  1. Nelson Cruz said,

    February 14, 2008 @ 12:23 pm

    Using electricity for heating is very inefficient. Most electricity is still produced by burning fossil fuels and converting the heat produced to electricity. The problem is only about a third of the heat is converted (33% efficiency). The theoretical maximum is 60% if I remember my thermodynamics classes correctly.

    And then, even more energy is lost traveling from the power plant.

    However if you burn something (like gas) directly in your house a lot less heat is wasted. A gas powered water heater is said to be about 85% efficient (some heat escapes up the smokestack). A gas powered air heater, the kind you place in your living room, puts all the heat to proper use! Some heat is still wasted with the extra ventilation required for safe use. A fireplace is likely very inefficient… but the fuel is renewable (usually wood, a form of biomass), so no net CO2 added to the atmosphere.

    So unless we start generating more than 66% of our electric power from Nuclear plants and renewable sources like wind and solar, electric heating is never going to be better in terms of CO2 emissions, and most likely cost as well. Currently the opposite is true. In the US more than 60% of power still comes from fossil fuels:

  2. Jeff said,

    January 10, 2009 @ 6:56 pm

    100 watt Edison bulb does not equal a 20 watt mercury CFL … it takes a 26 watt CFL … so you start out wrong by 30% …

    Most people claim that Edison bulbs waste 90% on heat … so your heat number is off as well … plus cfl’s contribute almost no heat (that’s why they are so efficient at generating light) …

    so to recap

    equal light
    inca bulbs = 72kwh = 96.5 pounds of CO2
    cfl bulbs (26watt) = 18.7kwh = 25 pounds of CO2

    equal heat I’ll assume 10 watts for the cfl (221,000 btu’s)
    23 pounds of co2 if heated via natural gas …
    86 pounds of co2 if heated via electricity …

    so the totals in wintertime are:

    with natural gas heat
    CFL bulbs = 42 pounds per day
    Inca bulb = 96 pounds per day

    with electric heat
    CFL bulbs = 111 pounds per day
    Inca bulb = 96 pounds per day

    gee … if I have electric heat maybe I should stick to inca bulbs …

    or better yet maybe I should use halogen bulbs ?

    100 watt inca = 65 watt halogen for equal light and heat …

    so the Halogen totals in wintertime are:

    with natural gas heat
    CFL bulbs = 42 pounds per day
    Halo bulb = 62 pounds per day

    with electric heat
    CFL bulbs = 111 pounds per day
    Inca bulb = 62 pounds per day

    yes the summer months mean more AC to counter the heat generated with either the inca or halo bulbs …

    of course in the real world most of us have at least 6 months of winter heat vs 3 months of summer AC …

    again if you have electric heat CFL is not the way to go …

    again who is running 30 bulbs 24/7 ? horrid example made even worse with sloppy facts (20 watt cfl = 100 watt inca ???)

    You are not saving the world by switching to cfl’s …
    You may be saving Al Gores investment portfolio but not the world …

    And all that natural gas that you are using which has to be TRUCKED to your house with a really nasty diesel engined truck … thats gotta count against your total CO2 output as well …

    Since we are now at a 10 year point with no global warming maybe its time to look up some real science and see for yourself that you’ve been conned …

    Facts are terrible things and correlation does not equal causation …

    So why do the facts show that there is a horrible correlation between global temperatures and CO2 levels ?

    In the last 100 years the largest long term drop in global temeratures (1940-1970) occured at the same time the largest increase in CO2 occured ???

    How can it be that Al Gores famous IC Ice Core Sample charts shows temperatures rising 800 years BEFORE CO2 rose ?

    You are being conned … wake up

  3. cec said,

    January 12, 2009 @ 10:04 am

    Awesome – trolls without understanding.

    Yes, I agree that a 100 watt incandescent is not a 20 watt CF bulb – this was the larger of the two numbers that Longman cited (he specifically said 15 or 20 watt CF bulbs were equivalent to 100 watt bulbs). I also agree that no one in their right mind is running 30, 100 watt bulbs 24/7 – again, that was Longman. Please read before commenting.

    Regarding your numbers, it’s difficult to follow your derivation, but the numbers themselves are flat out wrong. If you have an electric heat pump, then your heating is more efficient than using electric resistive heaters. This means that you are using less electricity with a combination of CF bulbs and heat pump than if you are using electric bulbs. Halogen bulbs are better than regular incandescents, but still not as efficient as CF bulbs. Finally, please remember that (essentially) all of a CF bulb’s wattage is converted to heat. Even the light energy converts to heat when it strikes an opaque object in the house.

    As to the global warming rants. Let’s see:

    * natural gas is often piped to homes (at least where I live).

    * no one’s talking about saving the world through CF bulbs, but every bit helps. moreover, this saves me money 🙂

    * regarding the 1940s to 1970s cooling period. I’m not certain what the relevance is. Yes, there was a cooling period, yes CO2 was on the rise at that time. There are any number of factors involved in the temperature of the planet and CO2 and other greenhouse gasses are only some of them. Most scientists point to sulphate aerosols due as being the “culprit” of the cooling period. These aerosols scatter the incoming light, reflecting some of it back out of the atmosphere. Climate models that include such aerosols demonstrate the same 1940s to 1970s cooling period. Finally, temperature *lags* CO2 in every rational climate model, so what’s your point?

    * regarding CO2 and ice cores. yes, there is a 200-1200 year lag in the historical ice cores (I’ve read the original research paper). But that’s completely irrelevant. We know that greenhouse gases hold in heat. If they didn’t, then the Earth would be significantly colder than it is now. We also know that green house gasses, specifically CO2, are rising right now and that the temperature is lagging the rise in CO2. Just b/c in past years, temperature preceded CO2 does not mean that’s the case here. Yes, when the planet heats, CO2 starts increasing in the atmosphere. Among other reasons, this is b/c a warmer ocean can absorb less CO2 (think of a warm coke). But the authors of the paper acknowledge that once CO2 started increasing, the temperature kept increasing.

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