Why is my pool water warmer at the deep end than the shallow?

[Freddie]

So this is throwing me off, I always thought shallow water heats up faster. But when I went for a swim yesterday, the deep end actually felt noticeably warmer than the shallow end. I don’t have a heater running, just normal circulation with my pump. Is it possible my return jets are pushing warm water down there and not mixing right? Or is something else weird going on with circulation? Never noticed this before, and now I can’t un-feel it.

 

[Isabella]

So this is throwing me off, I always thought shallow water heats up faster. But when I went for a swim yesterday, the deep end actually felt noticeably warmer than the shallow end. I don’t have a heater running, just normal circulation with my pump. Is it possible my return jets are pushing warm water down there and not mixing right? Or is something else weird going on with circulation? Never noticed this before, and now I can’t un-feel it.

That’s unusual, but not impossible. If your return jets are angled downward and most of your circulation flow is ending up in the deep end, it could trap warmer surface water down there while the shallow side stays cooler with more evaporation. I’d try adjusting the return eyeballs to circulate more across the surface and see if the temps even out.

 

[Zephyr]

So this is throwing me off, I always thought shallow water heats up faster. But when I went for a swim yesterday, the deep end actually felt noticeably warmer than the shallow end. I don’t have a heater running, just normal circulation with my pump. Is it possible my return jets are pushing warm water down there and not mixing right? Or is something else weird going on with circulation? Never noticed this before, and now I can’t un-feel it.

I had almost the same thing happen one summer. Turned out my shallow end skimmer wasn’t pulling much water, so circulation was super uneven. Deep end kept “collecting” heat, while the shallow end got cooled by wind and splash-out. Check your skimmer suction and make sure your pump basket isn’t clogged, sometimes that small stuff makes a big difference.

 

[Michael Young]

Sounds like a little ‘thermocline day.’ Light wind + returns angled down can push that warm surface skin downward along the slope, so the deep end becomes a warm pocket while the shallow end gets cooled by wind/splash evaporation. Quick check: use two thermometers one 8–12 in below the shallow surface, one near the deep bottom read them at the same time around 3–5 pm. If there’s a >2°F gap, you’ve got stratification. What fixes it for me: aim 1–2 returns slightly upward to create a gentle surface swirl, add an extra afternoon mixing cycle, and make sure the skimmer weir moves freely. Fun sanity test: drop a few ping-pong balls; if they all ‘park’ in the deep end, your flow is indeed diving there.

 

[Lily Allen]

This is interesting! It could be the depth affecting the water circulation. I’ve noticed before, the deep end can feel warmer, maybe because of the wind cooling the shallow part. Haha, now I’m curious to check the pool pump system again!

 

[Grace Hall]

Sounds like warm water is collecting in the deep end. Your return jets might be angled down while the shallow side cools from wind/evaporation. I’d aim the eyeballs a bit upward to sweep the surface, then run the pump 1–2 hours in the afternoon to mix it.