How-To: Lily Pad Pool Warmers

Lily Pad Pool Warmers from MAKE Volume 23

Lily Pad Pool Warmers from MAKE Volume 23

With temperatures on the rise and the first day of summer only 3 weeks away, pool season is just about upon us. Back in MAKE Volume 23, rocket engineer Edward Hujsak shared an efficient, low-cost, safe, and easy way to warm your pool. His project is the Lily Pad pool warmers, and they’re essentially made of hula hoops covered with black polyethylene film. The how-to is freely available for you on Make: Projects, where community member Daniel Busby commented, sharing the video he made of his Lily Pad build. The only difference between Edward’s instructions and Daniel’s build is that Edward used a soldering iron to spot weld the plastic to the hoops, and Daniel chose to use a household iron. Here’s Daniel’s video:

YouTube player

In his article, Edward also included an interesting sidebar titled “The Pool Owner’s Dilemma”:

The thermal behavior of swimming pools is complex, due to a number of factors that act to cool the water, while the sun and artificial means work to keep the water warm. Cooling forces are at work day and night, and include evaporation, conduction into surrounding soil, air current effects, and nighttime longwave (infrared) radiation into space.

Gas-fired heaters are the most common pool warmers, but up-front costs for equipment and installation run into the thousands of dollars. And then there’s the operating cost and the price of natural gas. These heaters are prodigious polluters; for an average-sized pool, a 1°F rise in temperature results in spewing 50lbs to 60lbs of carbon dioxide into the atmosphere.

Roof-mounted solar heaters are a second option. Water from the pool is pumped through solar-heated heat exchangers and returned to the pool. Like gas-fired heaters, solar heaters are costly and are generally unsightly. They’re also a problem in frost-prone areas.

Bubble plastic blankets are passive devices that cover the pool. They function mainly as water conservation devices by inhibiting evaporation, thus slowing evaporative cooling. They also block nighttime radiation loss. Manufacturers claim these blankets also behave as warmers, transmitting additional energy from the sun into the water. But water already has a very low albedo (ratio of incident energy to reflected energy). It’s about .10 for deep water, a bit higher in white-bottomed pools, and it’s doubtful that bubble covers improve on that. (The low albedo of water is the reason for the great concern about the receding of the polar ice caps. Open water warms much more rapidly than ice fields, which reflect more than 80% of the sun’s energy.) Moreover, pool blankets destroy the aesthetic appeal of a backyard pool; they’re hard to manage, difficult to clean, and unsafe where small children are around; and they’re often dumped after a single season.

18 thoughts on “How-To: Lily Pad Pool Warmers

  1. Eliot says:

    Dan Busby is the lead engineer at Syyn Labs

  2. lolokoliesko says:

    i think that is much easier to paint bottom of pool with black color – then colder water that is usually on lower levels can be heated and circulate.. or not? ;)

  3. lizzy peace says:


  4. Nathan (@Moriash) says:

    Or to make it massively more complicated and expensive for little benefit (beyond cool points), make them hexagonal, to fill in the voids when the breeze close-packs them against one side of the pool. (What? You don’t have hexagonal hula hoops at your local Toys R Us? Suppose you could make do with PVC pipes, six 60 degree elbows each.) Maybe embed strong rare earth magnets in the sides, perhaps two magnets per side, with the north side of one magnet a few inches from the left end and the south side of the other magnet a few inches from the right end. Provided you kept them all with the correct face upward, that would tend to snap them into the close packed configuration as the sides slid past each other. Probably wouldn’t work so well in the curved pool, though. Very silly, and next-to-no concrete benefit to doing that, but it’s fun to think about.

  5. DIY Pool Heater | House of Ellis says:

    […] and a roll of black plastic? Apparently you end up with a low cost and trendy looking pool heater! Read more here. Share […]

  6. r says:

    I think this is a great idea. wonder if there is a way to work a solar cell into the project tod something cool like circulate water along the top of the plastic surface to improve heating, or maybe circulate the pool water, or to have a downward facing LED that lights up the pool at night,
    I do like the hexagon idea above. The magnets are a great idea, BUT (!!) if you have a small child who falls in the pool, it would potentially trap the kid under the magnetic seals, so i would be VERY careful about it’s application.
    The black bottom pool is always a cool idea, but it looks so awful! I did so one in croatia that was made of the same black stone in the area that look mighty awesome. the rest I’ve seen look like moss ridden hell holes!
    How about an arduino drive mirror that reflects more light until the pool, or onto a black “obelisk” so that the is more concentrated heat transfer to a neat artistic structure

  7. Peggus says:

    Help fund Daniels beer habit and check out his other awesome projects like “A Movable Feast”:

  8. MAKE | Your Comments says:

    […] response to the How-To: Lily Pad Pool Warmers piece, user Nathan (@Moriash) has a novel idea: Or to make it massively more complicated and […]

  9. How To Make Lily Pad Warmers — Homestead and Survival says:

    […] How To Make Lily Pad Warmers […]

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I'm a word nerd who loves to geek out on how emerging technology affects the lexicon. I was an editor on the first 40 volumes of MAKE, and I love shining light on the incredible makers in our community. In particular, covering art is my passion — after all, art is the first thing most of us ever made. When not fawning over perfect word choices, I can be found on the nearest mountain, looking for untouched powder fields and ideal alpine lakes.

Contact me at or via @snowgoli.

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