Introduction: Turn an Old Coffee Maker Into an On-demand Water Heater (nevermind)

Picture of Turn an Old Coffee Maker Into an On-demand Water Heater (nevermind)

Update:  Nevermind this one.  Too many electrical shock risks to make it advisable even as an experiment.

Hey guys, this was a fun and novel idea I had but on retrospect, I don't think it's really something safe enough to recommend for people to try for realz, so I am deleting it...

Thank you for reading!

Step 1: Are You Forgetting Something?

Picture of Are You Forgetting Something?

Did you read all the safety warnings and follow them?

Are you sure you want to do this?

Did you feed the cat? 


Step 2: Bathtime

Picture of Bathtime

Fill up the tub as usual. 

The initial water temperature of the bath was 96 degrees.

Step 3: Enjoy a Long Soak

Picture of Enjoy a Long Soak

Read a book or watch all the Sketchup tutorial videos from the comfort of your nice warm bathtub.


Step 4: How Effective Is It?

Picture of How Effective Is It?

Thank you and stay safe.



cnathan (author)2013-01-17

I actually made a homemade water heater using a coffee maker and some other supplies. I travel in a motor home and do not like using LP gas so I ripped out the gas heater and built a rather cheap but efficient water heater. All in all, I spent maybe $60 to build and took a day to construct. I made a supply list and step-by-step instructions but it's not letting me add photos. I made a 20 gallon tank and it takes about 6 to 8 hours to get around 110-130 degrees. The only problem I have had with it so far is if I use well water, I have to clean the water lines once a month as lime and calcium build up. I use vinegar to clean lines.

foobear (author)cnathan2013-01-18

Awesome, good to hear that this idea can actually work. I got so much flack for this one that I deleted most of the article. Maybe you will post an instructable that people will appreciate.

Rayvillian913 (author)2010-11-28

Used this years back to heat a hot soaking tub for my wife. You don't need a pump just put the coffeemaker at the water level of the tub and add a siphon hose to put the water back in the coffeemaker tank, that will make the two water level stay equal. Works great except the pot would calcium up after about 2 months of continual use and have to be replaced. I've since gone to a 5 gal bucket heater and a waterbed thermostat teaked a bit to raise the temp to 110 degrees.

foobear (author)Rayvillian9132010-11-28


desertdog (author)2010-11-28

Interesting approach. Reminds me of a guy I know that used the heating element from an electric hot water heater heater to achieve the same thing.

As far as I know he is still alive.

DragonDon (author)2013-10-18

Well this is disappointing. Heck, quite a few things here are a 'bad idea if you don't understand the risks'.

foobear (author)DragonDon2013-10-19

Yeah, I tried to delete this one, but it was in a contest, so I couldn't

mikesnyd (author)2011-01-23

What is the aproxima GPM output of hot water? Thanks. I was just wondering how long i am going to have to wait for a tub to be filled. I have a small 100L tub i want to fill for my camping expiditions. due to the girlfriend not wanting to camp unless she has hot showers/baths everyday. Thanks

tinstructable (author)2010-12-31

Can someone say sketchy? Haha, don't kill yourself with a coffee maker next to a bathtub.

Cartuner55 (author)2010-11-28

Damn, forgot to feed the cat.

KadenP (author)Cartuner552010-12-05

So did I. Anyone want to loan me a cat so I can feed it and get past step 3?

fly_boy_bc (author)2010-11-29

Why not READ the instructable before submitting a critical comment?

"Not sure it wouldn't be easier just to turn on the hot water to re-heat the bath"

The FIRST PARAGRAPH tells you why he does not do this.

I have EXACTLY the same problem AND I have a spare (and gutted) coffemaker I was using as a distillery. I will be lounging in warm water all night!

siwasher (author)fly_boy_bc2010-11-30

Sorry for overlooking that point, but I wasn't being critical. I love the idea.

espdp2 (author)2010-11-29

That's what the cat is for!

fly_boy_bc (author)espdp22010-11-30

Of course! That's why we had to feed the cat! He's our TEST BATHER!

Ultra-Indigo (author)2010-11-29

You don't need to start a siphon the coffee maker already does that normally when you use it to make a pot of coffee. That is why the water in the tank in the back of the pot doesn't get hot and all the hot water ends up in the pot. The key is there is a ball valve inside the heating element so when the water heats up it expands and creates lower pressure on the hot side drawing in the cold water past the ball valve which in turn gets heated up. That is why you don't have a pump on the coffee maker in the first place.
The ball valve is also the part that gets kludged up with lime and you have to clean it with vinegar or it gets too hot and you burn out that little heat fuse. I like the bike tire (cheap and easy) but it might be better with silicone tubing to withstand the heat hate to have the tube leak in the middle of a nice bath.

Oroka (author)2010-11-28

Interesting project, but how big is your water heater? Unless it is teeny tiny, you should be getting a lot more hot water out of it. Perhaps a element is burned out or something.

foobear (author)Oroka2010-11-29

It has just enough capacity to fill the tub once only. It requires a 30-40 minute wait to heat up all its water again.

Oroka (author)foobear2010-11-29

wow, that is quite small.

Used hot water heaters really are not that expensive. As long as the tank is solid, the rest of the tank is pretty simple.

foobear (author)2010-11-29

I assume you mean the hot water outlet of the coffee maker and not the tub.

foobear (author)2010-11-29

Certainly, don't try this at home.

jptrsn (author)2010-11-28

Check out

It explains how the coffee maker works without a pump. That means that if you take the heater assembly, hack both hoses into the tub, and keep the whole thing lower than the water level in the tub, it should work without a pump.

Use really long hoses, and you won't have the safety hazards that this project entails.

Let us know if you work on it more! 

foobear (author)jptrsn2010-11-28

I like this idea. It's very simple. I'm not sure how to easily get the siphon started to get the water flowing from the tub to the element though.

jptrsn (author)foobear2010-11-29

If you've got enough of a length of tubing, getting the siphon started is pretty simple. I use the following method for cleaning my fish tank and draining the swimming pool:

1) Submerge as much of the tube as you can in the water.
2) Cap the open end of the tube (a thumb comes in handy here).
3) Pull the tube out so that the water in the tube goes up over the edge and comes down to a level lower than the surface of the water.
4) Remove thumb.

As long as the water in the tube is lower than the surface, the pressure differential will push water through the tube. Get the water going, then raise the open end of the tube and put it back in the tub. As long as it's primed to the heater element, it'll draw cold(er) water from the tub.

foobear (author)jptrsn2010-11-29

I see what you're saying. I'd like to find an easier way though.

espdp2 (author)foobear2010-11-29

How about one of those squeeze bulbs for a marine outboard motor's fuel tank? A few squeezes will push water up and over the edge of the tub, and the bulb will let it keep flowing in that direction.

foobear (author)espdp22010-11-29

The problem is you'd have to somehow squeeze it from the device side to get the cold water flowing into it. Just having trouble visualizing how to hook that up.

DeusXMachina (author)2010-11-28

Using something like that, I think you could come up with a slightly more elegant and less dangerous kludge.

foobear (author)DeusXMachina2010-11-29

interesting. I didn't know about this device. thanks

computurwizard (author)2010-11-29

If you are gonna play around with this, then you need to replace the electrical outlet in your bathroom with a GFCI outlet and make sure the coffeemaker is properly grounded. PLEASE do this, it could save your life!

foobear (author)computurwizard2010-11-29

I thought GFCI outlets were required by code in all bathrooms. I don't know. Maybe not in every state.

foobear (author)2010-11-29

Definitely don't try it if you feel like that. Stay safe.

sheilamommy (author)2010-11-28

Room's ambient temp 51 degrees. And I thought I kept my house on the cool side. I will show your instructable to my kids to let them know how goodthey've got it at 65 degrees.

foobear (author)sheilamommy2010-11-28

Yes, I bought an old fixer upper and it has no insulation anywhere! So, even with all the heaters on and the fireplace, we couldn't keep it warm enough. Outside was 20 degrees or so.

espdp2 (author)foobear2010-11-29

Hire a teenager to put in some fiberglass and spray-can insulation. It will save you lots of money over running the heaters and fireplace. Anything is better than a drafty box.

Also, you should look into a pellet stove. They are just about the greenest heating solution out there, not TOO terribly expensive, and easier than a fireplace to keep going.

foobear (author)espdp22010-11-29

certainly good advice

foobear (author)2010-11-29

Thanks, that was constructive feedback.

fly_boy_bc (author)2010-11-29

This is exactly the way to do it and I assumed it was the way this instructable worked before I read it. Really easy to imement and no syphoning difficulties.

I think it will be easy to make sure it is safe too. Just make sure there is no way for the coffemaker element to get wet. (on he outside) NO danger.

WingDings (author)2010-11-29

:D Lethal!

Rayvillian913 (author)2010-11-29

I use an old water bed heater for the heatpad for seed starting. Put the heater in the bottom of a wood box with 1x4 sides. put a plastic sheet to keep water from the heat element than 1 1/2" wet sand on top to spread the heat out. Thermostat bulb buried in the sand controls it. You have to add water occasionally.

abfarrer (author)2010-11-28

Ok, I can see you hesitance to have gas installed to make for more hot water, but do yourself a favor, and look into electric on-demand water heaters. you can get small "point of use" models that mount under a sink, I'm sure you can find something that would fit your needs far more safely than this contraption.

Of course, it will cost you more than $10.

Spokehedz (author)2010-11-28

Nice... Like the sous vide heater in the kitchen. :P

gijoebob (author)Spokehedz2010-11-28

I was thinking the same thing.

JesusFreke (author)2010-11-26

Now you just need a small water pump to pump water from the bathtub into the reservoir. Your local hardware store likely carries a small desktop water fountain style water pump. I had got one for around $25 iirc.

Although, you would probably need some sort of water level sensor/cutoff for the reservoir too, otherwise you'll end up overfilling or under filling it.

foobear (author)JesusFreke2010-11-27

I love those fountains, they seem full of hack potential. I saw one at Goodwill yesterday for 8 bucks and thought it was too pricey. Tempting though...

joeny1980 (author)foobear2010-11-27

Nah, the pump element alone is only a few bucks . I bought one from Home Depot for like $6. Your combination of electricity and water is scary, but probably the most dangerous thing here is using that glass carafe in a tub. Imagine hitting the edge of the tub and breaking it. With shattered clear glass IN the water, next to your naked body... definitely extremely dangerous.

I also think you can get rid of the body of the coffee maker and add a much larger reservoir.

foobear (author)joeny19802010-11-27

Yeah, I only added the carafe part back in because as it's running, you can see all this extra heat from the heating element is just being wasted. I wanted to reclaim it somehow, putting the carafe full of water on there was all I could think of.

mary candy (author)2010-11-26

the cat is so cuuuuteeeeeeeee

foobear (author)mary candy2010-11-27

yes she is a super awesome cutie, with a fun loving little personality too

Rainh2o (author)2010-11-26

Why not just pump the water through the heating element refill, no worry about overflowing the water resevoir, and if you had a long enough hose, you could set it far away from the tub all together.

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