My laziness gets me in trouble

Fire in a fireplaceIn my last post, I pointed to Wired’s article on heating vs cooling as a singular good article in the lackluster series. I did admit that they didn’t give much in the way of detail, but figured that was just a result of the space limitations.

Well, I should have been less lazy and taken a closer look. The online version of the article includes links to their sources and it turns out that Wired is comparing a one-room AC unit in Phoenix versus a whole-house furnace in New England. No wonder the New Englander fares so poorly!

I can see why they did that, though. It’s a lot harder to compare actual numbers than to fil out a state in an online calculator (that doesn’t explain how it arrives at its numbers). Apart from the difference in size, it also seems odd to me that they chose fuel oil, since most homes (that aren’t heated by electricity) are heated by natural gas.

With those criticisms in mind, I ran my own numbers, often using the same sources as the Wired article. Here’s what I turned up.

The Wired article says that the New Englander produces 13,000 lbs of CO2 in a season. Based on their source for pollution figures, that comes out to 80.55 million BTUs for the season. If they used natural gas instead of fuel oil, it’s only 115 lbs of CO2 (rather than 161 lbs) per million BTU, meaning that a home using natural gas instead produces only 9290 lbs of CO2 a season.

However, I found a NYT article that states the average New England home uses 65,000 cubic feet of gas per season. Using Wired’s source for pollution levels, natural gas produces 120.593 lbs of CO2 per thousand cubic feet.

Instead of 13,000 lbs of CO2, the average New Englander probably produces more like 7,840 lbs of CO2!

Now for the other side of the equation, which was quite a bit harder. I tried to estimate the size of the AC unit needed to cool a house but couldn’t find any numbers that matched. Eventually, I hit upon the idea of using the government’s energy efficiency rating (SEER) to figure it out.

In 1997, the average AC SEER was 10.66. Since it’s now illegal to sell AC systems of less than 13, I’ll assume that the average has moved up to 12 by now. As a side note, window units aren’t required to meet this standard, so they tend to be less efficient.

The average American home is 2349 square feet(!) according to the National Association of Home Builders (in 2004, so it should match well with the heating data I had from that year). A 12 SEER air conditioner uses 100 kWh per MBTU (by definition). Dividing the house size by 1000 gets us 2.349 MBTUs required to cool the house. According to a Kansas State University study, houses in the south west use 12 times the base rate per season, so the total MBTU needed is 28.188. Times 100 kWh gives us 2819 kWh for the season.

Arizona’s power is relatively clean compared to other states, since it mixes coal (bad) with nuclear (good). In terms of lbs of CO2 per kWh, Arizona is maybe a little high at 1.56, much higher than Idaho, which is far and away the best at 0.03, but significantly better than the worst, North Dakota at 2.24.

Given the energy usage for the season, the typical Arizona home will produce 4400 lbs of CO2 (2819*1.56).

Wired’s final numbers were 900 lbs for cooling and 13,000 lbs for heating, an incredible win for cooling. My numbers show that it’s much closer, with 4,400 lbs of CO2 produced while cooling and 7,840 lbs for heating. It’s sad that Wired couldn’t run the real numbers, since they support its point, although not by such a ridiculous amount.

Of course, the real numbers are much more nuanced. If you use passive solar in New England, you’ll cut your emissions considerably. By the same token, a geothermal heat pump in Arizona would significantly decrease your AC usage. And, in either place, a smaller home reduces your emissions. A better point than encouraging cooling over heating would have been to encourage people to get smaller houses.

Too bad that conclusion wasn’t sensational enough for Wired. this!

6 Responses so far »

  1. 1

    arduous said,

    June 20, 2008 @ 1:13 pm

    Thanks for running the numbers correctly, Will. I did think Wired’s basic point (that it cost less to cool 20-30 degrees than it cost to heat 40-50 degrees) made sense, but I had also noticed that they were comparing a house to a room. Dumb.

    One of the nice things about living in LA, is I realize I don’t really need either the heat or the a/c. It really never gets cold. It does get pretty hot, but since I work outside the home, I don’t need to turn on the a/c in my apartment. Once it hits night, it’s cool enough that just an open window will do.

  2. 2

    Will said,

    June 20, 2008 @ 3:14 pm

    I do enjoy Wired’s longer articles, but since everything is online (with supporting links!), I’m seriously considering cancelling our subscription.

    That’s great! Not having to heat or cool is huge. I’m pretty sure that we heat and cool quite a bit more than we would if I didn’t work at home. On the other hand, I think we make up for that with reduced transportation needs, so it’s probably a wash.

    I do find myself sleeping later and staying up later now that it’s gotten warmer. I have a hard time falling asleep when it’s too hot, but if I wait until it’s late enough, we get a cool breeze and I don’t have to turn on the AC!

  3. 3

    Emily said,

    June 22, 2008 @ 3:42 pm

    Wow! Thanks for the impressive math. 🙂

    Do you have any good figures for heating with wood?

  4. 4

    Wil said,

    June 22, 2008 @ 6:15 pm

    It’s a lot harder to measure the impact of wood, since all of its carbon is biogenic (a part of the natural carbon cycle). However, if you want to cut carbon emissions overall (perhaps to offset other people burning non-biogenic carbon), wood produces about 195 lbs of CO2 per million BTU. If you’re like the typical New Englander, you produce 65.1 million BTUs in a season. That’s 12,695 lbs of CO2 (not far off from Wired’s original assumption!).

    That’s a lot, but as I mentioned, that’s biogenic carbon, so most of it would be released into the atmosphere anyway, through (forest) fires or decomposition, so I find it hard to say that burning wood is worse than burning natural gas.

    Also, people who heat with wood tend to be better about heating just a portion of their house (because it’s easier), so my guess is that wood-burners actually produce a lot fewer BTUs than the average person.

  5. 5

    Kirsten said,

    February 12, 2009 @ 12:24 pm

    Also, people do not realize it but much of the southwest has heating days in winter, so factored over a year, including the heat for the winter the numbers might be a lot closer.

  6. 6

    Will said,

    February 12, 2009 @ 12:31 pm

    That’s a good point, Kirsten. My grandparents live in the mountains of New Mexico and they get at least as much snow as we do here in Indiana, which implies to me that they’d probably use as much heating as we do.

    And, on the other side, I bet there are some places in New England that need cooling in the summer.

    It’s a complicated subject!

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