Episode 89: Exploding Water Heater

Air Date: November 7, 2007

A water heater can explode and shoot through the roof of a house like a rocket.


In small scale testing, the Mythbusters started with a small six gallon water heater and disabled all of its safety features under the theory of poor installation or neglect. While the water heater eventually ruptured, it did not explode like a rocket. The Mythbusters then upgraded to larger thirty gallon water heater which exploded with significantly greater force, sending the water heater several hundred feet into the air. In order to confirm the stated myth, the Mythbusters obtained a full size fifty two gallon water heater and built a shack around it with a roof that followed standard California building codes. The water heater eventually exploded, shooting through the roof five hundred feet into the air and disintegrating the shack. In light of these results, and the fact that there is documented evidence corroborating the myth, the Mythbusters deemed it confirmed.

(The MythBusters revisit this myth in Myth Evolution to see if a water heater can explode through the roof of a two-story house.)

If a person is being dragged by a horse, the friction caused by the movement will make their jeans catch on fire.


Wearing full body padding and a denim shirt and jeans, Tory allowed himself to be pulled along the ground by a horse. While the movement and friction did increase the surface temperature of the jeans, it wasn’t enough to cause the jeans to combust. The Build Team then moved the experiment into the lab, where they simulated the friction caused by being dragged by a horse with a power sander. However, when they applied the jeans to the power sander, the jeans were torn apart before they could combust. The Build Team agreed that friction alone cannot make jeans catch on fire.

Shrinking jeans while wearing them in a hot bath for six hours can kill you.


The theory behind this myth is that if a person wore a pair of jeans and sat in a hot bath intending to shrink them to fit, the shrinking jeans can cut off blood circulation to the legs which can cause a lethal clot or require the legs to be amputated. The Build Team experimented with a pair ballistic gel legs with tubes running through it to simulate blood vessels. They then covered the legs in jeans and put it in a hot bath for six hours, but found no change in blood flow. They then had Grant wear a pair of blue jeans and had him sit in a hot bath for six hours. During the experiment, Grant was continually monitored by a medical expert and by the end of the six hours, he was declared healthy and in no risk of death. The Build Team decided that the myth was busted, but reminded the audience that blood clots and cutting off blood circulation are very real dangers and should not be taken lightly.


  1. thedanc says:

    Like the 747 v taxi, the water heater wasn’t much of a myth. This is clearly plausible from the onset and so the episode was just a demonstration. It was the coolest thing I’ve ever seen on TV though! Since there is NO WAY I’d try this at home, I really enjoy the show.

  2. Mike Hughes says:

    I have also heard of an exploding water heater. I really like the way you scientifically approach all of the myths. The problem I have with your water heater test is that the tank was made into a sealed vessel by plugging the water inlet line and T&P valve. In a real house with all safety devices disabled the pressure in the tank would surely increase but not higher than the incoming line pressure from the street main, rarely higher than 125 psi. The presure would push back into the street main. I do really enjoy the show.

    • Plausible says:

      That would only be true if there wasn’t a pressure reducing valve on the incoming water line. That’s why expansion tank are required when a pressure reducing valve is installed. That would prevent the pressure from pushing back into the street main.

  3. Mike says:

    About the shrinking jeans myth, it was a girl who bout jeans that was skintight to begin with, and then went swimming in them, and let the sun dry them on her.

  4. Jombi says:

    For the hot water heater myth:

    The myth was whether or not the hot water heater would launch like a rocket or explode like a bomb.

  5. Sciencegalage11 says:

    Hey, last year, for the Science fair I dicovered that if you shake hairspray up ( in a arisol can) then spary some in a cap without a hole the cap will explode because of the reaction of the carbon dioxide in the unstable inviorment. (that was my concution in the fair, I would have won, exept I had umonia and couldn’t show up in time so I was diqualafied) This from a 10-year old!

  6. Dan says:

    I do Oklahoma’s longest-running morning radio show (26+ years!)…but on Jan. 20th, 1982, I was going to report on some small story, when I heard the Star Elementary School in Spencer, OK., had exploded. The hot water heater beside the school’s cafeteria had a jammed relief valve, and the explosion killed 6 students, and one teacher. We had media from all over the country come to cover the tragedy, even landing helicopters in the parking lot of a funeral home next door to the school. I even personally had to put out a grass fire across the street, started by a non-moving line of cars that had gathered to witness the
    carnage, and their catalytic converter
    under the car caught the grass on fire! I’ll always remember that day, as will most Oklahomans…and it’s proof a water heater CAN be deadly.
    Dan Stroud, KXY Radio

    • Cassandra H. says:

      I was in the cafeteria at Star when this happened. I was in 4th grade. I was seated on the same side of the cafeteria as the hot water heater at the last table furthest from it. It seemed to happen in slow motion, but I remember seeing the ceiling peeling upward as if I were on the inside of one of those old-timey sardine cans that you had to use a key to roll the top back with. When it started to come back down, rebar, dust, and cinder block chunks were falling everywhere. When I looked behind me, I realized that the blast had pushed our table about 15 feet back closer to the back wall. I don’t remember hearing the blast, just watching as the roof peeled up like that. One of my friends was up closer to the lunch line and said he remembered flying high up in the air. The hot water heater was found in the playground. So, yeah, this was no myth to begin with. But I don’t remember anyone having burn injuries. Wouldn’t the lunch ladies have gotten burned, especially since the cash register was right next to the closet where the heaters were? That is a day all of us who were eating lunch will remember. I try to see what I can find about it every Jan 19th. If anyone runs across any of the old newspaper articles on this, there was a picture of a child’s lower legs and feet and the rest was hidden by a hedge or bush. Makes you think that it was a dead body, but no, it was me. We had to wait sooooooo long for the emergency crews to arrive because dispatch had sent them to Star Spencer High School instead of Star Elem. School in Spencer. I had nightmares for years and still get very nervous when I see a cylinder shaped hot water heater.

  7. William says:


  8. Mike Itnyre says:

    I am a vivid fan of Myth Busters. I am fully aware of hydro dynamics However there is one built in safety system on a hot water heater. The incomming water connection. If all of the other safey devices were disabled the increased pressure would simply over come the incomming water supply pressure. This would occure at 100 PSI or less and the hot water heater would stay well within it’s rated pressure. Results no explosion. This of course if the water service has not been shut off. So there you have it 3 safety devices.

    Thanks, keep the episoids comming

    • Plausible says:

      pressure reducing valve can keep the pressure in the house water system, doesn’t allow back flow. that why expansion tanks are required to be installed when prv’s are installed.

      • Ffjohn says:

        I second that, a coworker of mine had one detonate in an apartment fire. Obviously a lot of heat involved but somewhere the lines where sealed and boom.

  9. Steve says:

    The hot water heater explosion referenced in the show occurred in Burien, Washington located 10 miles south of Seattle. For a link to the story go to http://www.komotv.com/news/archive/4014621.html The water tank went through a large beam and 2×6″ car decking (flat roofed building) before coming to rest some 460 feet away. The rear of the store was cinder block and was blown out by the blast. The small strip mall was later torn down due to the damage. A plumber had capped the relief valve believing it was defective. He had intended on returning the next day to replace it.

    Another water tank explosion occurred in Kent, Washington in the early 80’s. The hot water tank was located in the basement of a church. It caused significant damage when it rocketed through the roof of the two-story building coming to rest in an adjacent lot.

    Love the show!

  10. Jon Tuck says:

    I want to point out a couple of things that you need to consider.It is the fact that most municipalities in urban areas now have backflow preventers at the meter or where the water line enters the building, this creates a “closed system” this arrangement WILL allow pressure to build to extermely high levels, Thermal Expansion tanks and relief valves limit the pressure to less than the rating of the T+P valve. You must also consider the incoming static pressure starting at 55 or 60 psi, this baseline pressure would help the problem happen faster, It all must work together to be safe
    Questions welcomed

  11. Dylan B. says:

    I personaly love your show.You should try a florida myth.try if you have a fanboat in the back of a pickup truck the fanboat can push the truck.Oh by the way I am 10.

    Please write back Adam.

  12. Kusumura says:

    Jeans can kill you? I’ve swam around in a pool for about 8 hours with my clothing on to test this at home (Aswell as it being a Saturday night party =P) and erm.. Well. If you tire out too quickly.. But that’s in a pool or the ocean. If you manage to tire out in a bathtub, you have some *deep* issues to sort out.

  13. David says:

    In reply to Mike about the pressure not exceeding city pressure, that is mistaken. A pressure reducing valve, check valve or most newer water meters would restrict backflow into the city water supply, which is why most locations require a seperate expansion tank be installed now to give the pressure somewhere to go or it can build and leak at the T&P valve even under normal conditions.

  14. Paul Malley says:

    Jeans Can Kill You

    The one parameter you didn’t appear to control was the water temperature.

    You simply left your man in the tub for six
    hours letting his skin go wrinkly.

    Water temperature is very subjective, the
    lady wife does washing up in water that
    scalds me.( I mow the lawn)

    Put a sample of denim in water at a controlled temperature, then check the ammount it has shrunk, you could also put
    a force meter on another sample and check
    the force it can exert whilst trying to shrink, then do your tests again.


    Replace the sandpaper on the belt sander
    with a lenght of denim.
    Increase the speed of the sander by a factor of five or ten.
    If gas will burn it, so will friction

  15. Robert Bogden says:

    Hi- Love the show. I would like to see Tori and Grant do more controls (or at least talk about them on the show) for their experiments. For example- with the pig blood/denim jean shrinkage experiment: there should have been a negative control and positive control (tubing running through tub without any possibility for constriction-proves pig blood is not coagulating), and a positive control- another tube that they artificially constrict to show that the pump and blood flow can be constricted (perhaps the pump was compensating for any constriction).

    As scientists, we know that proper controls are fundamental to doing good research. Plus you guys are responsible for teaching viewers about how scientists think! :)


  16. Michael H says:

    How long did it take for the water heaters to hit the ground after exploding? The 30 gallon went “several hundred” feet and the 52 gallon went “five hundred” feet.

  17. Gerrie van Deventer says:

    Water Angel.An early warning detection system on your geyser to protect the geyser from exploding.Also a electricity saving device.www.waterangel.co.za

  18. Nathan says:

    For the jeans catching on fire, I agree the sanding belt should not be sand paper but something with a high coeficiant of friction but low abrasiveness. it might even catch on fire at the speed they were useing, but if not certianly a higher speed would catch them on fire.
    The hot water tank… AWSOME!! I am watching a rerun of it right now!!

  19. Katchall says:

    Id like to know whether a water heater would explode and burn down a house due to “flammable” fumes in the same room – a storage room.

  20. jeff long says:

    did they say how high it went?

    • Carmen says:

      did you read the summery?

  21. c says:

    Does anyone know, or did they mention on the show, why the hot water tank always failed down and rocketed up? Is it designed to do this? Wouldn’t it be safer to have it fail up, rocket down (since these usually sit on a ground or sub-ground level) and have it pushed itself into the earth? I admit I know little of water heaters but this diagram: http://homerepair.about.com/od/plumbingrepair/ss/hwh_tank_gas.htm –doesn’t show any feature that would make it consistently fail down and rocket upwards. Any thoughts?

  22. James Denson says:

    I have not seen the episode, but I was an eyewitness. I was in third grade, I believe. I was sitting in the opposite corner of the cafeteria and our class was very close to taking our school trays back to the front. There was a sudden explosion and I put my head down and covered with my hands. When it was over I looked up and saw the opposite corner of the cafeteria collapsed, teachers and students screaming, and dust everywhere. I believe this may have something to do with my later mild asthma. By the way, my younger brother was outside on the playground where the water heater landed.

  23. Jason O'Dell says:

    I have not seen the eppisode either but I was an eyewitness to the Star Elementary Explosion in Spencer, Oklahoma. I was in 1st grade and on the playground when the water heater exploded. I really don’t remember much of what happened but I do remember the explosion, the cinderblock wall falling and the screams of the other children and adults.

  24. Garr says:

    Well, I love this show and I rather enjoy the way you guys perform your tests. My only question on this episode is this: where can I get the body armor that Tory wore to perform the “being dragged behind a horse” test?

  25. Phill says:

    What if the cowboy had some NOT SAFETY matches on his back pocket?

  26. Danny Coffey says:

    I to remember the day of the explosion I was a boiler and pressure vessel mechanic at the time. today I am a licensed boiler and pressure vessel mechanic and licensed boiler operator.

    But people still don’t relize what power a water heater can have, But we in Oklahoma know what can happen when not cared for, Their families still miss Them.


  27. felixnoir says:

    In Melbourne, Australia, in April or May 2011, a factory was badly damaged by a badly-maintained exploding water heater that ended up in a yard 200 yards away. I hope I’m remembering the newspaper story correctly.

  28. Rick Norvell says:

    I am a licensed plumber in Alaska and am very concerned about the comments from others about the water heater explosions being a myth as the pressure will back up into the main.The problem nobody is understanding is steam that occurs when the tank overheat as a result of low water and or bad thermostat. Water will expand something like 1600 times in an instant when it goes from water to steam, and is very explosive. It is not water pressure itself that is the problem, but instant steam volume. Think 1600 water heaters full of water at the same time, and all trying to occupy the space of one!

  29. Richard L. Manning says:

    I remember vividly the Star School Cafeteria Disaster. I worked in the Midwest City Police Dept. Records Division and was on duty when the incident occurred. I am also a former student of Star School and was familiar with that cafeteria layout. It was my responsibility that fateful day, to keep a running log of casualties and contacts with family members for our department. It was a very sad duty dealing with the families involved. I learned later that my father had just passed the school in his car when the explosion demolished the cafeteria. There is a memorial bench located at the former school site, remembering those who perished.

  30. Enrico Martinez says:

    WHY IN THIS EPISODE 89 “A water heater can explode and shoot through the roof of a house like a rocket.” IS CONFIRMED???

    WHILE IN EPISODE 85 “Aerosol cans placed in an open fire can explode with lethal force.” IS BUSTED???

    If a water-heater can punched through the roof like a rocket; so does an aerosol-can can explode (and hit a person) with lethal force.

    They are both sealed cylinder metal, and both subjected to heat. They just differ in size, but very much alike in lots of properties.

    SO… DO THE MATH!!!!


    • Golfball says:

      @Enrico: In order to make the comparison you are making, the pressure required for the individual vessels to fail would also need to be similar, this is not the case. (Aerosol cans are only rated for 200psi, significantly lower than the 300psi of water heaters, and aerosol canisters burst (from the top) at temperatures below the boiling point of water.)

      The burst aerosol can will not be moving nearly as fast (and is much smaller) than the hot water heater. In order for a flaming aerosol can to be lethal (even if both water heater and flaming aerosol are moving at the same speed), the can would have to be much heavier.

  31. Harry says:

    My experience is you can compress air not water.
    I would think under most conditions the tank would
    rupture rather than turn into a projectile.

  32. Greg says:

    Episode 71 is inaccurately linked to this episode.

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