If you’re a pool owner (or considering getting one) and you’ve ever stared at that chilly blue water in early spring or late fall, wondering “when the heck can I actually swim in this?” you’ve definitely wondered about pool heat pumps. And if you’ve come to me as a pool heat pump supplier (I won’t name drop, but I’ve sold hundreds of these bad boys to homeowners, resorts, and even small apartment complexes over the last 8 years), the #1 question I get is: “How fast can these things actually heat my pool?” Pool Heat Pump
Spoiler alert: it’s not magic, but it’s way better than heating with a gas heater (and way cheaper long-term). Let’s break this down like I’m chatting with you over a beer after a long day, not writing a college thesis. No confusing jargon, just real stuff I’ve seen firsthand.
First, let’s get one straight: there’s no universal “one-size-fits-all” number. A lot of guys online will say “your pool heats 1 degree per hour” but that’s only true for super specific conditions. Like, if you have a 10,000-gallon small plunge pool, it’s mid-80s outside, no wind, direct sun? Sure, maybe 1 degree an hour. But if you have a 20,000-gallon big family pool, it’s 50 degrees outside, windy, and it’s early March? Don’t expect that same speed.
Let’s start with the basics of how a pool heat pump even works, because if you get that, the speed makes way more sense. Unlike a gas heater that burns fuel to make heat, a heat pump steals tiny bits of heat from the air (even when it’s cold outside! Down to like 40 degrees, it still works) and concentrates that heat to pump into your pool. Kinda like how your fridge sucks heat out of its inside to keep your milk cold, just reversed.
Now, the things that actually determine how fast it heats your pool. I’ve listed these out a million times for customers, and they’re the ones that actually move the needle:
- Your pool size (duh, but let’s be specific)
This is the biggest one, no contest. Let’s do quick math because I’m not trying to bore you, but it’s necessary. Pool volume is measured in gallons, right? For a rectangular pool, it’s length x width x average depth x 7.5. For round, it’s radius squared x average depth x 5.9. Got that?
Example time: A small 10,000-gallon plunge pool (like for a small patio) vs. a big 25,000-gallon standard family pool. To heat that pool 1 degree Fahrenheit, how much heat do you need? 10,000 BTUs. Wait, BTU is the unit we use for heating, right? So 10,000 gallons = ~10,000 BTUs to raise 1 degree. That means a small pool only needs 10k BTUs for 1 degree, while a 25k-gallon pool needs 25k BTUs for 1 degree. Makes sense, right? More water = more stuff to warm up.
So if you have a 50,000-gallon commercial pool? Yeah, that’s going to take way longer than a small backyard pool. I had a guy last year who bought a heat pump for his 40k-gallon pool and texted me after 2 days saying “it’s only warmed 5 degrees!” I didn’t panic, because that’s exactly what the math said it would take—he just had a way bigger pool than he thought.
- The heat pump’s BTU rating
This is the next big one, and this is where a lot of people mess up. They buy a cheap, tiny 30k BTU heat pump because it’s cheaper, then wonder why it takes forever to heat. Let’s pair that with our earlier example: a 25k-gallon pool. To heat 1 degree, it needs 25k BTUs. A 30k BTU heat pump would put out ~30k BTUs per hour in ideal conditions, so that would be almost exactly 1 degree per hour. But if you buy a 20k BTU unit for that same pool? Now you’re only getting like 0.75 degrees per hour, so 1 degree would take 1.3 hours. That adds up fast.
Pro tip from me: Don’t underbuy your heat pump. I see this all the time—people trying to save a few bucks upfront, and then they’re stuck waiting weeks for their pool to be swimmable. Rule of thumb: For residential pools, you want a heat pump rated for at least 80-120% of your pool’s volume in BTUs. So a 25k-gallon pool? Go for a 20k to 30k BTU unit, not a 15k. For commercial or bigger pools, we size them a bit higher because they get more use.
- Outside air temperature and wind chill
Here’s the thing about heat pumps: they get way less efficient when it’s cold outside. Even though they work down to 40 degrees, their output drops a lot when it’s chilly. A heat pump that puts out 30k BTUs when it’s 80 degrees outside might only put out 18k BTUs when it’s 50 degrees outside. That’s a huge difference!
And wind? Wind is the enemy here. If it’s 50 degrees but windy, it feels like 42 degrees, and that drops the heat pump’s output even more. I had a customer in Michigan last spring who thought his heat pump was broken because it only heated his pool 2 degrees in 6 hours. Turns out it was a super windy week, and his unit was sitting out in the open with no wind block. Once he put a small fence around it to block the wind, it jumped back up to 1 degree per hour.
Also, direct sun! If your pool is in full sun all day, that’s free heat. So if it’s 70 degrees outside, sunny, your pool might even heat on its own a little, plus the heat pump can take it the rest of the way faster. If it’s shady all day? You’re losing that free heat, so the pump has to work harder.
- Pool cover usage
Oh my gosh, this is the #1 hack I tell every customer, and 90% of them don’t use it at first, then come back a month later saying “why didn’t you tell me this?” A good pool cover (a solar cover, not the cheap flimsy ones) cuts down on heat loss by like 70-80%. When your pool is uncovered, all the heat you pump in evaporates right into the air. If you cover it when the pump’s running, that heat stays in the pool.
Let’s put this in perspective. If you have a 25k-gallon pool, uncovered, in 70 degree weather, you might get 0.8 degrees per hour. Cover it? That jumps to 1.2 degrees per hour. That’s 50% faster! I always include a free roll of solar covers with every heat pump I sell, because I’d rather my customers get the performance they expect, not some random number from a textbook.
- Water features and filtration
Wait, what do water features have to do with heating speed? Evaporation, that’s what. If you have a water fall or a spa jets running all day, that’s adding more evaporation, which means more heat loss. Same with running your filtration pump 24/7 (wait, no—wait, you do need to run your filtration, but running it longer than needed will pull heat out too). So if you turn off unnecessary water features when you’re trying to heat the pool, that’s another small boost.
Now, let’s put all this together with real examples, so you can see exactly what to expect. These are all actual pools I’ve installed or sold units for, so no made-up numbers:
Example 1: Small residential plunge pool (10,000 gallons)
- Heat pump: 20k BTU (properly sized)
- Outside temp: 80 degrees, no wind, full sun
- Cover used: Yes
- Expected heating speed: 1 degree per hour. So if your pool is 50 degrees, it will take about 30 hours to get to 80 degrees (swimmable temp for most people). That’s a long weekend of running the pump, which is totally fine.
Example 2: Standard family pool (20,000 gallons)
- Heat pump: 25k BTU (properly sized)
- Outside temp: 65 degrees, light wind, partial sun
- Cover used: Yes, only when the pump is running
- Expected heating speed: ~0.7 degrees per hour. So from 55 to 80 degrees? That’s (25 degrees needed) / 0.7 = ~36 hours. Still manageable over a week.
Example 3: Big family pool (25,000 gallons, plus a small attached spa)
- Heat pump: 35k BTU (oversized a bit to handle the spa too)
- Outside temp: 55 degrees, medium wind, shady most of the day
- Cover used: Sometimes, when I remember
- Expected heating speed: ~0.4 degrees per hour. Oh wow, that’s slow. From 50 to 80? That’s 75 hours, or over 3 days straight. Which is why I always tell people to make sure they size for their actual conditions, not just the pool size.
Wait, but what about when it’s super cold? Like 40 degrees outside, windy. I had a customer last year in Minnesota who wanted to heat his 22k-gallon pool from 45 to 75 degrees in February. I sized him a 35k BTU unit, but warned him it would be slower. Turned out, it only put out ~15k BTUs that cold, so heating speed was ~0.68 degrees per hour, so that took about 44 hours. Which was still way faster than a gas heater would have done, and way cheaper on the electric bill.
Now, let’s bust some common myths, because I hear these every single week:
Myth 1: “Heat pumps can’t heat my pool in cold weather.” Nope, they just get slower. If you want to swim in early spring or late fall, you can still do it, you just need to size your pump a bit bigger, and use a cover. I’ve had people swim in their pools in Ohio in mid-April, when it’s 50 degrees outside, with a properly sized heat pump.
Myth 2: “My pool heats 1 degree per hour, always.” No, that’s only in perfect conditions. If you say that, you’re either lying or testing in a lab. Real life has wind, shade, covers you forget to use, etc. So expect a little less, not a little more.
Myth 3: “I can use a smaller heat pump to save money.” Like I said earlier, this is a trap. You’ll save $200 upfront, but you’ll be waiting weeks longer for your pool to be swimmable, and you’ll end up paying more in electricity because the pump is working way harder to heat the pool slower. Proper sizing is worth every penny.
Now, what about the actual cost? Wait, you asked about speed, but people always ask this too. A pool heat pump costs way less to run than gas. For example, heating a 20k-gallon pool 25 degrees would cost about $15-$25 in electricity, vs. $100-$150 with gas. That’s why even if it takes a little longer, it’s a no-brainer for most people.
Here’s the thing I always tell customers: the speed of your pool heat pump isn’t a random number. It’s all about matching your pump to your pool size, your local weather, and how you use your pool. If you do it right, you’ll get your pool swimmable in way less time than you think, and you’ll save a ton of money over the years.
If you’re still not sure what size heat pump you need, or you want to know exactly how fast you can get your pool heated, I’m here to help. I’ve been doing this for long enough that I can look at your pool size, your local average temperatures, and give you a real, honest estimate—no sales pitches, no hidden fees, just what you can actually expect. Whether you’re a homeowner with a small backyard pool, a resort with multiple pools, or an apartment complex looking to add heat, I’ve got units that fit every need and budget. Don’t guess and end up waiting forever for your pool to be warm—hit me up to chat through your setup, and we’ll get you sorted.
R32 Monobloc Heat Pump References:
- American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). 2021. HVAC Applications Handbook.
- Pool & Hot Tub Alliance. 2022. Residential Pool Heating Guide.
- U.S. Department of Energy. 2023. Residential Pool Heating Efficiency.
- International Association of Plumbing and Mechanical Officials (IAPMO). 2021. Pool Equipment Installation Standards.
Guangdong Luckingstar New Energy Co., Ltd.
Guangdong Luckingstar New Energy Co., Ltd. is well-known as one of the leading pool heat pump manufacturers and suppliers in China. Please feel free to wholesale high quality pool heat pump from our factory. For customized service, contact us now.
Address: No.255 Hexiang East RD, C Area Heshan Industrial Zone,Heshan City, Guangdong, P.R. China
E-mail: info@luckingstar.com
WebSite: https://www.luckingstar.com/
