I’ve been scoping out kerosene stoves for eventual use on a sailboat, and I keep coming across various BTU ratings for them.

A little investigation reveals that the unit they are really talking about is “BTUs per hour”. A single BTU, according to Wikipedia:

A BTU is defined as the amount of heat required to raise the temperature of one pound of liquid water by one degree from 60° to 61° Fahrenheit at a constant pressure of one atmosphere.

All this talk of BTUs for stoves was fine for comparing one stove to another, but what I was really curious about is how my cheesy little kitchen stove compared to a kerosene stove. I decided to try and measure the effective BTUs of my favorite burner.

Experiment-wise, I figured that I could provide the one pound of water, and that I had the equipment suitable for measuring time and temperature (as long as the temperature change was large enough). And one atmosphere of pressure was roughly available here in Ann Arbor (850 feet above sea-level).

I was going to have to fudge the whole “60° to 61° Fahrenheit” thing, what as I wasn’t expecting my cute wireless meat thermometer to be that precise.

The procedure I settled on was to pre-heat the burner (on high), then pre-heat the pan I was going to use (so that the burner wouldn’t be heating the pan so much as heating the water).

Then I would take the (starting) temperature of the water. At that point I would pour the water in the pan and start a timer.

I decided to let the timer run for two minutes, hoping that the temperature change would be large, but not push the temp too close to boiling (where things get all latent-y). Pouring out the water and measuring the final temperature would give me all the data I needed.

The final temperature did flirt with boiling at 170º, so one minute would have probably been a wiser choice, but I figure that I got away with two minutes. The math at that point is pretty simple:

(Final temperature minus starting temperature) times 30 = effective BTUs per hour.
(170 – 56) * 30 = 3,420

(If I — or you — were to use one minute instead of two, ‘times 30′ would become ‘times 60′.)

I am aware of the fact that I strayed 110º away from the 61º that is the official reference, but am willing to live with that. Switching to one minute would get me closer to something more scientific, but I like that large temperature change for its measurability.

The big take-away from the experiment? Well, I’m guessing that the burner I was testing is rated somewhere between 8,000 and 10,000 BTUs/hour, but I was able to get less than half of that into the water. Interesting. I wonder where the larger figures come from?

I’m looking forward to getting my hands on some Kerosene burners to test. Leave a comment here if you come up with any interesting numbers of your own, thanks.

Extras:

There are 3.41 BTUs per hour in 1 watt, which means that my burner was getting around 1,003 watts of energy into the water. Sounds about right.