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Cool Hand Luke Meets Air Conditioners

Rules Of Thumb Often Lead To Oversized Air Conditioners

Using the wisdom of Cool Hand Luke to explain building enclosures, mechanical systems, or indoor air quality is a long established tradition in building science.  Joe Lstiburek’s Cool Hand Luke Meets Attics is the pinnacle of this genre, of course, but other seminal works in this line are Cool Hand Luke Meets Ventilation and Heating by John Shaw Billings, Cool Hand Luke Meets Water in Buildings by Bill Rose, and Cool Hand Luke Meets the Insulated Man by Professor John Strauberry.*

I’ve attempted many times to foray into this arena but have always ended up deleting what I had written.  My hesitation stems  from my fear of failing to communicate clearly.  The Building Science Fight Club can be ruthless, you know.  Nevertheless, I’m going in deep this time, even if I do end up with egg on my face.  You may think I’m bluffing, but this time I’m ready.  I have no intention of digging my own grave.

Cool Hand Luke as an air conditioner

What is Cool Hand Luke most famous for?  Eating 50 boiled eggs in one hour.  That makes him like an air conditioner, which eats heat from inside your home.  Luke ate 50 eggs in one hour,** and that was his absolute maximum egg-eating rate.  What is your air conditioner’s heat-eating rate?

Let’s say you have a 2 ton air conditioner.  Because of those 19th century guys with their scary tongs and huge blocks of ice, we know that 2 tons of air conditioning is equivalent to 24,000 BTU per hour.  That’s how much heat your air conditioner can eat.  That’s its capacity.

Cool Hand Luke has a capacity of 50 eggs per hour.  That’s it.  And we know that’s his maximum capacity because he just barely got that 50th egg down his throat in the last second.

Matching capacity to load

Mechanical equipment works best when its capacity is close to the load.  For Luke, the load would be the number of eggs he needs to eat per hour.  A healthy adult male eats about 2,400 kilocalories (usually called calories) per day, or 100 kCal per hour.  A boiled egg has about 78 kCal in it, so Luke really needs to eat only 1.3 eggs per hour.

I’d say he was way oversized for this job since his egg-eating capacity is about 39 times higher than his egg-eating load.  Is it any wonder he could hardly move after his feat!

It’s the same thing with your house.  If you have a 2 ton air conditioner and a half ton cooling load, the air conditioner is oversized and somebody’s not going to feel so good.  You’ll probably have the sweats one minute and chills the next.  It won’t be pretty.

The Cool Hand Luke solution to oversizing

Having an oversized air conditioner can be a problem.  But the wisdom of Cool Hand Luke goes far beyond attics.  Here’s what you need to do to get your oversized air conditioner’s capacity to be a closer match to your load by following Luke’s example.

Start by boiling 50 eggs.  Peel them all, and divide them equally into two bowls.  Take one bowl to the part of your air conditioner that sits outside and smash the eggs into the air conditioner coil on that unit.  You want to reduce the total air flow by a little less than the amount that you’re oversized.  If you’ve got a 2-ton air conditioner serving a half ton of cooling load, you should try to spread those 25 eggs out over about 60 to 70 percent of the coil. That’ll leave you with the capacity you need plus a little extra.

Air conditioner outdoor unit buried in mulch
Air conditioner outdoor unit buried in mulch, an alternative to the Cool Hand Luke method of reducing capacity [Photo credit: Howard J Saunders, HVAC Hacks]
Then you take the other 25 eggs and smash them into the return grille inside your home to reduce the amount air being drawn in to match the reduction in the outdoor unit.  This is important because you don’t want your air conditioner to be unbalanced in any way.

There you have it.  An fictional solution to a real problem.  If you try it and it doesn’t work, get in touch with me because my micro-split heat pump should be for sale by the time those eggs in your air conditioner start smelling bad.


Allison Bailes of Atlanta, Georgia, is a speaker, writer, building science consultant, and founder of Energy Vanguard. He is also the author of the Energy Vanguard Blog and is writing a book. You can follow him on Twitter at @EnergyVanguard.


* There are so many deserving works in this genre but I really can’t write this article without mentioning two more:  “Cool Hand Luke Meets the Energy Nerd” by AJ Builder and “Cool Hand Luke Meets Honest Buildings” by Henry Gifford.

** By the way, Luke’s feat was great in the movie but pales in comparison to the real-life record:  141 eggs in 8 minutes.


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