This summer’s record-high temperatures have sent us all running for the pool.
As the nation’s 5.4 million in-ground residential swimming pools do their part in keeping us cool, we began to get curious about how much energy they use.
It’s been estimated that 9-14 billion kilowatt hours of electricity are consumed each year just to maintain these 5.4 million swimming pools. That’s more electricity than is used each year in 11 individual US states and Washington DC. It’s as if all the retail electricity consumption in New Hampshire could grind to a halt, and then be routed to power the nation’s swimming pools.
So we wondered: how much more energy does a home with a pool use each year, relative to a home without a pool?
To investigate, we examined energy consumption data from 2 million homes (all with gas space-heating) in a climate-moderate part of the Western US, representing a mix of pool homes and non-pool homes. We were able to identify homes with pools by cross-referencing anonymous, publicly available property records. Then we looked to see if any patterns emerged related to pool ownership and energy use.
A pattern emerged: pool homes annually consume 49% more electricity and 19% more natural gas than their non-pool neighbors. The result for a pool owner is approximately $500 per year in higher energy bills – and nearly double that in states with higher electric and gas prices.
But the question remained: is this ~$500 difference in energy consumption strictly due to the energy requirements of maintaining pool? Or are there additional factors at play? Let’s dive into the analysis…
Exploring reasons why pool homes use 49% more electricity per year than non-pool homes
Let’s consider three key factors that contribute to pool owners’ high energy bills: 1) the pool itself, 2) large home size, and, 3) lifestyle.
1. Pumping and filtering 20,000 gallons of water is extremely energy-intensive
The strongest driver of pool homes’ high energy use is…the pool! Let’s take a look.
It takes a lot of electricity to continually pump and filter the ~20,000 gallons of water that typically fills a US in-ground residential pool. It’s an astonishing amount of water: the average human being drinks only about 15,000 gallons of H2O in their lifetime. A pool pump uses more electricity than any other appliance in the house except the air-conditioner.
Motivated by regulatory requirements, new pool pumps are becoming increasingly energy-efficient, but existing pumps’ electricity consumption has been estimated at a whopping 2,000-2,500 kilowatt-hours per year. At the national average electricity price of 11.8 cents/kWh, a pool pump can add upwards of $250-$300 to a family’s annual electricity costs.
Heating the pool can also be a major driver of pool-related energy use, especially when the pool is left uncovered. Pool heating is almost always done by natural-gas heaters (or in some regions by solar water heaters), rather than by an electric heater, and can be costly: even occasional heating can add $100-$250 to one’s yearly gas bill. However, very few pools—by one credible estimate, only about 10% of them nationwide—are heated. Likewise, our data reveals minimal difference in swimming-season natural gas usage between pool homes and non-pool homes. This suggests that residential pool heating is indeed rare, and therefore has minimal significance for our analysis.
So if pool pumping represents a little over half of the energy consumption difference between pool homes and non-pool homes, then what other factors may account for the rest of difference?
2. Homes with pools are bigger
As you might predict, homes with pools tend to be larger than homes without pools. Bigger homes mean higher energy usage. The average pool home in our dataset was 2,052 square feet. That’s 21% larger than the average non-pool home (1,693 square feet).
We saw above that the average pool home uses 49% more electricity and 19% more natural gas per year than the average home without a pool. But would we still see this big of a difference if we only compare homes of similar size?
Confining our analysis to 40,000 homes of similar size (2,500-2,600 square feet), we found that the energy consumption gap between pool homes and non-pool homes becomes only somewhat smaller: pool homes of ~2500 square feet still consume 42% more electricity and 14% more natural gas than equivalent-size homes that don’t have a pool.
The bottom line: homes with pools are larger, and the larger home size itself does appear to account for greater energy consumption. But only by a little bit.
3. Across the (diving) board, pool owners are likely to carry on a high energy consumption lifestyle
Our data suggests that pool owners systematically use more energy for reasons beyond their energy-intensive pool pump or their large home size.
We found that pool homes use significantly more electricity and natural gas than similarly sized non-pool homes in all 4 seasons, rather than just during the peak-swimming summer months. Even considering that some pool owners are likely to run their pool pump periodically in non-swim months to keep the water clean and pretty, the fact that pool homes use significantly more energy in every season (see the electricity usage pattern for similar-sized homes below) points to behavioral differences that may go beyond maintaining a pool.
A couple of lifestyle-related explanations for pool homes’ higher energy usage throughout the year may include:
• Pool homes have more occupants. Our demographic data from the Western US shows that homes with pools have on average 9% more children (1.18 compared to 1.08 children) than non-pool homes. It seems reasonable that a family with kids would be interested in a yard with a backyard pool. At the same time: more kids = more humans using energy around the house.
• Pool homes have a higher income. Data from the Association of Pool and Spa Professionals indicates that the median income for households with in-ground pools is $104,000 per year (double the national median income). Higher income implies a greater likelihood to own additional TVs, a second refrigerator, and other discretionary appliances.
In other words, a swimming pool may be a canary in a coal mine of high household energy consumption.
Some friendly cost-saving advice to neighbors with pools
We’ve seen that the pool itself is the largest driver of pool homes’ high energy usage. Fortunately, there are some simple steps that a homeowner can take to save hundreds of dollars each year on pool-related energy costs…
• Use a pool cover. First, a cover keeps the pool water clean, which means that the energy-intensive filter pump doesn’t need to run as much. In addition, a cover can reduce evaporation from the pool by more than 90%, which saves a lot of water (and keeps the water warmer). Without a cover, the entire 20,000 gallons in the pool can evaporate each year, and refills aren’t free. Replacing all that water can easily add more than $100 to a pool owner’s annual water bill in water-scarce regions.
• Install a variable-speed pump. A “variable-speed” pool pump is critical to maximizing pool energy efficiency. In contrast to a standard “single-speed” pump, a variable-speed model alternates between slow and fast modes to optimize energy use throughout the day, reducing pump electricity consumption by up to 75%. Many utility companies offer a significant rebate upon purchase of an efficient pool pump.
• Reduce pool pump run-time. Many pool owners simply run their pool pump longer than is necessary to keep their pool clean. It’s best to determine the minimum required run-time and stick with that. In one study, pool owners in Florida who reduced their pumping time to less than 3 hours per day were still happy with their pool’s water quality.
In the meantime, don’t forget to work on the efficiency of your swim stroke.
Special thanks to Chris Tan, Efrat Levush, Jillian Cairns, and Arhan Gunel.
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Methodology Notes: Data is based on a sample of 2.04 million homes– a mix of pool homes (318,000) and non-pool homes (1.72 million)–in the Western US. For comparability of energy usage across the homes considered, this analysis is strictly confined to homes with gas heat. Energy cost estimates are based on national average 2011 energy prices: $0.118/kWh and $1.08/therm. Estimate for lifetime water-drinking is based on a pool with approximate dimensions of 18 ft x 30 ft x 6 ft, a rule-of-thumb turnover time of once per day, eight 8-ounce glasses of water per day, and an 80-year life expectancy. Due to the relatively moderate climate in the Western US and exclusive consideration of gas-heat homes, the reported results for annual per-household electricity consumption are lower than the US national average of 11,500 kWh/year.
Data Privacy: All data analyzed here are completely anonymous and treated in strict adherence to Opower’s Data Principles.
Author’s note: The analysis and commentary presented above solely reflect the views of the author(s) and do not reflect the views of Opower’s utility partners.