Picture of Pool Heating XL-Lily Pads
First off, respect and credit to Make Zine and Cogzoid for sparking this idea. I modified their designs and instructions to make the project cheaper and more cost efficient.

Summer is upon us and that means it's time to open the pool. However, I don't have a pool heater, or the desire to spend thousands of dollars on one. After surfing the net I found a solution I liked: the so called lily pad passive pool heaters, and made it better!

Why Lily Pads?
  • They heat- by attracting and keeping more solar energy in the water
  • They slow evaporation- by forming a barrier between the air and the water
  • They are easy to use and store- just push them aside or stack them on the deck
  • They're safe- no solar blanket to get tangled in or caught under
  • They're cheap- ten for $35 (Pro versions will run you $25 each!)
  • They're green- they use no gas or electricity to heat, conserve water, and can last several seasons

We'll be making ten 4.77' (about 4' 9.25") lily pads. That's a combined surface area just shy of 180 square feet. That should cover a good chunk of just about any residential sized pool.

This project involves hot irons, please be careful.

Step 1: Materials and Tools

Picture of Materials and Tools
I bought all of my materials from Lowe's for a total of $35. Assuming you have to tools this shouldn't cost you a dime more.

  • Black plastic sheet, 10' x 25', 4mil (in building materials section)
  • 1/2" Black irrigation tube, 200'*
  • 10 1/2' barbed tube couplers
  • Vinyl electrical tape
  • Silver marker (anything that will mark on black plastic)
  • Measuring tape
  • Scissors
  • Saw
  • Soldering iron
  • Household Iron
*For this project we will only use 150', but I could only find 50', 100', and 200' rolls. Since 15' doesn't divide nicely into 50' or 100' you need to get the 200' roll and figure out something fun to do with the extra 50'. Also, the 200' roll was only a few dollars more then the 100', so it's cheaper this way.
HidiousTak3 months ago

I wonder if some kind of reflective surface on the bottom would heat the pool too.

Terranan3 years ago
Black garbage bags could make it cheaper...
CYNICALifornia (author)  Terranan3 years ago
I considered those, but they are generally a lot thinner and wouldn't make the 5' x 5' square I needed. Good thinking though.
50" x 64" (when split) and 3 mil thick. Not quite large enough for your home-made loops but big enough for hula hoops, at least the unweighted toy hula hoops for kids sold at our local HEB supermarket/grocery for a buck or two, which I think are about 3' across.
dmatusicky gtoal5 months ago

I was thinking use some pool noodles, zip ties, and a garbage bag.

freetrapp made it!5 months ago
Bought the supplies just like the instructions said. Great step by step. Very easy. I made mine a bit smaller to store them easier.
zubain2 years ago
I was wondering if an HDPE sheet (density 0.95 to 0.96) or LDPE sheet (density 0.92 to 0.94) would float on the water without a frame. This would be easy to cover the entire surface of the pool. To help the sheet to float, perhaps straight lengths of plastic pipes, sealed at both ends could be used as floats. The pipes could even be attached to the sheet for easy rolling up when not in use.
leonardipc2 years ago
A small line of silicone glue, do much more than an iron or soldering without the danger of burning. Sorry translator.
How did these survive the summer?
CYNICALifornia (author)  winston_smith2 years ago
I did not respond quickly as summer was a bit long this year here. They did fanrastic! They are not brittle or faded at all.
CYNICALifornia (author) 2 years ago
I did not respond quickly as summer was a bit long this year here. They did fanrastic! They are not brittle or faded at all.
gtoal3 years ago
Could you use a piece of tubing to mould a plug using oogoo instead of buying those barbed couplers? The smaller tubes of caulk they sell at the dollar store ought to make enough rubber. The stuff seals well, I've used it myself.
Rebreg3 years ago
one made of duct tape would be easier
l8nite3 years ago
cool? idea! I have some thick black plastic laying around and a couple of hulahoops..have to see if the hulahoops float
CYNICALifornia (author)  l8nite3 years ago
As long as you tape the seam where the two ends meet, you should have no problem.
the hula hoop didn't float real well, not to be deterred I looked around and realized I hada small pile of extra sections of automatic pool vac hose, 4 pieces made a nice size ring and I ziptied on rounds of thick black plastic, 3 "lilys" covered a good amount of the pool... now if it would just stop raining I can see how effective they are !
nrvalente3 years ago
Hi! Nice instructable! Two questions:
How many ºC degrees did the water temperature increased with these pads?
Why do you poke holes in the plastic?
CYNICALifornia (author)  nrvalente3 years ago
Thank you.

I don't know. I don't have a thermometer and haven't had a properly sunny day yet. However I have an unheated spa and there was a noticeable temperature difference. I may go buy a thermo to find out.

The holes allow the air bubbles to escape from under the lily pad or water to flow from on top. They keep it nice and tight on the surface.
Very clever!