Introduction: Pool Heating XL-Lily Pads

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.

Step 2: Step 1 - Make the Hoop

Picture of Step 1 - Make the Hoop
In both the video's referenced, they used hulahoops. While theirs were awesome, I wanted larger lily pads and didn't want to pay high prices for a bunch of hulahoops. Here is the solution: make our own hoops.
  1. Measure and mark 15' from the end of the tube
  2. Cut at the mark
  3. Using the cut tube as a reference, stretch, mark, and cut nine more 15' lengths
  4. Lay a tube so it lays flat
  5. Seat one end of a barbed coupler in one end of the tube
  6. Seat the other end of the tube to the other end of the barbed coupler and push them together
  7. Tape the joint for good measure
  8. Repeat for the other nine lengths

Step 3: Step 2 - Cut the Plastic Sheet

Picture of Step 2 - Cut the Plastic Sheet
This is easy! The ultimate goal is ten 5' x 5' squares.
  1. Unroll a length more than 5' off the roll of plastic sheet
  2. Measure and mark 5' from the edge
  3. Cut at the mark
  4. Unfold the sheet and cut down the center crease
  5. Repeat for the rest of the roll
If your roll doesn't have a center crease just measure, mark, and cut at 5' again.

Step 4: Step 3 - Attach Plastic Sheet to Hoop

Picture of Step 3 - Attach Plastic Sheet to Hoop
This is the only tricky part, and it's not too bad. What we're going to do is weld the plastic sheet to the hoop.
  1. Preheat iron to medium (I used level 4 of 7)
  2. With the plastic sheet laying atop the hoop, press the iron against the top edge of hoop
  3. Hold with light pressure for about one second, then remove
  4. Continue doing this, working your way around the entire hoop
  5. Cut off excess plastic sheet from around the hoop
  6. Using a hot soldering iron poke a few (5-9) holes in the plastic sheet
Perfect! You're done! Now repeat this step nine more times.

Tips for using the iron to weld the plastic sheet to the hoop:
  • Take your time and go easy
  • Do this over a heat resistant surface (tile, concrete, etc.)
  • Angle the iron so it leans away from the hoop. This was any accidental melting will be on the excess to be cut off
  • Be careful about leaving hot irons around the house


JGDean (author)2017-06-06

I'll bet it would work to just laminate black (or blue or green if you can get them) vinyl sheeting (drop-cloth-type sheet, black is available at local home improvement centers) to bubble wrap. The size of it really doesn't matter as long as you cover most of the pool. Making them in smaller pieces (the lily pad concept) is a great idea. The solar covers sold through pool supply stores are expensive and hard-to-handle.

MeinardP1 made it! (author)2016-06-13

My 1st attempt at an Instructibles build..... was much easier than expected. I did use silicon glue as suggested in a comment instead of melting the sheeting to the tubes to save our house iron and seems to be holding up well. Going to make some smaller rings to fill the gaps with the leftover materials. Considering this 100% successful..... minus the cloudy days we're having at the moment.

Terranan (author)2012-06-05

Black garbage bags could make it cheaper...

CYNICALifornia (author)Terranan2012-06-05

I considered those, but they are generally a lot thinner and wouldn't make the 5' x 5' square I needed. Good thinking though.

gtoal (author)CYNICALifornia2012-06-22

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 (author)gtoal2015-03-23

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

GennieP (author)dmatusicky2016-01-16

I was thinking about trying this. We're you at heating your pool with noodles, zip ties, and garbage bags? This seems like the simplest, cheapest way to do it.

GennieP (author)GennieP2016-01-16

We're you successful at heating your pool?

dmatusicky (author)GennieP2016-01-16

We were swimming not long after this, but im not really sure how much had to do with the "lilypads" to be honest. I also learned to run the pump at night. Apparently running it during the day causes heat loss. So that could have been a factor.

HidiousTak (author)2015-06-02

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

freetrapp made it! (author)2015-03-14

Bought the supplies just like the instructions said. Great step by step. Very easy. I made mine a bit smaller to store them easier.

zubain (author)2013-07-16

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.

leonardipc (author)2013-01-22

A small line of silicone glue, do much more than an iron or soldering without the danger of burning. Sorry translator.

winston_smith (author)2012-09-12

How did these survive the summer?

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)2012-12-01

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.

gtoal (author)2012-06-22

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.

Rebreg (author)2012-06-16

one made of duct tape would be easier

l8nite (author)2012-06-06

cool? idea! I have some thick black plastic laying around and a couple of hulahoops..have to see if the hulahoops float

CYNICALifornia (author)l8nite2012-06-07

As long as you tape the seam where the two ends meet, you should have no problem.

l8nite (author)CYNICALifornia2012-06-08

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 !

nrvalente (author)2012-06-06

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)nrvalente2012-06-06

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.

SelkeyMoonbeam (author)2012-06-04

Very clever!

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