When are things good enough?

Way back in the Jurassic when it was brand new, our old boiler was maybe 60 percent efficient – that is, it burned only slightly more than half of the natural gas it sucked in. Put another way, 40 cents of every dollar spent on heating was literally going out the chimney as uncombusted fuel. When we bought the house, of course, the boiler was A) no longer new and thus much less efficient, and B) leaking more gas than it burned. But let’s be generous and say the old guy was 55 percent efficient.* With a monthly heating bill that sometimes topped $400, that’s a lot of lost green – and literally tons of unnecessary CO2 emissions.

You’re going to see huge savings – financial and environmental – moving from 55 percent to 85 and above. According to our friends in the government, upgrading from a 55 percent efficient boiler to a 90 percenter will keep 1.5 tons of CO2 out of the atmosphere every year. For us, a 30 percent gain in efficiency would be at least a hundred bucks off our monthly heating bill during winter, and probably $50 a month on average. If you pull out your slide rules, you’ll find that means over 60 months we’d save $3,000 – the cost of a new boiler – giving us a simple payback period of 5 years.

So the equation should be simple: Get the most efficient boiler, save the most money and energy, right? Well, sort of. Obviously, replacing a 55 percenter with a boiler that burned at 97 percent would save many more tons of energy over its lifetime than, say, an 85 percenter, or even a 92. Right on, go green and all that. Financially, the picture’s a little different.

Here’s one example. We looked at a popular little item called the Munchkin – a sealed combustion, condensing boiler – that runs at 92 percent. On sale (which it has been for almost a year from this friendly retailer – free shipping!), the unit we’d need costs $2,125. Using it, we’d gain 37 percent in efficiency – and in dollars. If we spend $1,000 a year on heating (entirely likely here in Boulder), we’d save $370 a year. The boiler would pay for itself in about 6 years, well short of its 15- or 20-year expected lifetime. Handy, right?

Another boiler worthy of our lust was a Buderus, really the Benz of boilers: sealed combustion, condensing, with an almost astonishing 97 percent AFUE – and small enough to hang on the wall. (Sweet!) But it costs nearly $2,000 more than the Munchkin. And that 5 percent gain in efficiency would save us only another $50 a year – it would take 40 years to pay back that $2,000 difference in upfront costs.

But is 92 percent good enough? Depends on your measuring stick.

===

*Just a note on efficiency: With all the percentages, I’m speaking of a boiler’s Annual Fuel Utilization Efficiency, or AFUE (“A-few”), a measurement set by the feds. Technically, the AFUE is the ratio of heat output of a furnace or boiler compared to the total energy consumed by a furnace or boiler. But I think of it as how many of my dollars are being wasted on uncombusted fuel: An 80 percent AFUE means 20 percent of my heating bill is, in effect, for nothing.