Anyone have a heater but no spa?

[djdonte]

Our pool does not get warm enough to swim in until mid to late May, even though the ambient temperature starts getting hot well before that. Same for the close of swim season, the pool gets cold while it's still hot enough to swim outside. I chalk it up to the pool being so close to the house that it does not get a ton of direct sunlight all day. We are thinking of installing a heater to extend our pool season. Is this a dumb idea?

 

[Bperry]

Our pool does not get warm enough to swim in until mid to late May, even though the ambient temperature starts getting hot well before that. Same for the close of swim season, the pool gets cold while it's still hot enough to swim outside. I chalk it up to the pool being so close to the house that it does not get a ton of direct sunlight all day. We are thinking of installing a heater to extend our pool season. Is this a dumb idea?

People do that all the time. I have one but the heat exchanger died and I haven’t replaced it yet.

 

[sande005]

Mine has had one for over 30 yrs. Just signed a contract to replace, since the now second one finally wore out! If I waited for mother nature here in Minnesota, swimming would only be July 4-Labor day. It was worse when we bought the house, and two gigantic pine trees shaded the pool for 90% of the day....

That said - it takes a LOT of BTU's to heat water. My home furnace is about 70K btu's, and it keeps the well insulated house nice even at -30F. My pool heater is 270K btus - almost 4 times bigger. It roughly takes an hour to raise the water temp 1 degree. (Yeah, I simplify way too much - a host of different factors at play here, but you get the idea...)

So it is a must for me to have to extend the pool season. Just that I have to watch over it, as the bill a month later sometimes results in me having to sell many, many nice things....

In Texas, you may want to delve into the economics of heat pumps vs conventional heaters.

 

[SJPoe]

Our pool does not get warm enough to swim in until mid to late May, even though the ambient temperature starts getting hot well before that. Same for the close of swim season, the pool gets cold while it's still hot enough to swim outside. I chalk it up to the pool being so close to the house that it does not get a ton of direct sunlight all day. We are thinking of installing a heater to extend our pool season. Is this a dumb idea?

We have an inground pool in Mid-Michigan. 5 months of the year, it's too cold to swim regardless of the pool temp

The other 7 months, we heat the pool. Yes, it's worth it. We typically open the pool mid-late April (yay, only another few weeks!!!), and last year we swam until October 18th. Most people around here are opening Memorial Day to Labor Day, and most aren't doing much swimming until late May...

The May gas bill can be a bit...spicy...but I think I worked it out once where it ended up costing me like a couple bucks a day over the course of the season, and having a warm pool for 7+ months of the year was worth way more to me than a Starbucks coffee. My wife is also of the opinion than anything less than about 85F is 'freezing', so we tend to have it set pretty warm. There is some fairly easy math you can do to come up with a rough idea of what the costs would be - but your mileage will obviously vary, and there are a lot of factors around size, shape, sun-exposure, ambient temperature, wind and so on that all contribute to your heat loss/demand.

If I had to replace the heater, I'd maybe consider a heat-pump setup rather than Natural Gas, but I haven't run the actual numbers to see where the break-even point would be.

 

[djdonte]

You hit the nail on the head. Our pool is typically open Memorial to Labor day, yet it stays hot for 1-2 months before and after that in Texas. Heat pumps are not very popular here, I think due to the hot climate we have but I am not an HVAC expert. I calculated roughly 360 sq feet of surface area on my pool so I'm thinking a 150-200K BTU natural gas heater.

 

[SJPoe]

You hit the nail on the head. Our pool is typically open Memorial to Labor day, yet it stays hot for 1-2 months before and after that in Texas. Heat pumps are not very popular here, I think due to the hot climate we have but I am not an HVAC expert. I calculated roughly 360 sq feet of surface area on my pool so I'm thinking a 150-200K BTU natural gas heater.

In theory, a heat-pump would be BETTER in a hot climate for heating something...as there is more ambient heat available to start with. The newest generations are good enough that they can generate 'heat' for the house in as low as -15F outside weather...

Like I said, I haven't dug into the relative costs/efficiencies but I think it would definitely be worth it for a new-install.

 

[gkw4815]

Your pool must be particularly shady...I'm also in the Houston area and we started swimming a couple of weeks ago. Pool is currently at 79 with no heater use. When we covered the pool at the start of November last year (just ahead of leafpocolypse) the water was in the low 80s and swimming was still comfortable.

We do have a gas heater but 99% of the time it's only used to heat the spa (roughly once a week all year long). We might run it enough to heat the whole pool to 85 for an early March weekend.

Two considerations specific to a gas heater on a spa-less pool in Houston:
-it isn't great for your heater to sit idle for months at a time. Good to fire it up for 30 minutes or so at least once or twice a month all year long (but only if the water temp is above 68 degrees so as not to suffer corrosive condensation damage).
-Note that if you heat your whole pool during months with mild to warm days and cool nights (March, November, and sometimes April) you will lose a lot of water to evaporation.

 

[Buggs]

Our 400K BTU heater gets a workout every year - usually all season long due to the cool Idaho nights. We're on our 3rd heater in 27 years, the current one installed in 2021. Last year we extravagantly enjoyed our pool later than usual - deep into the unseasonably-mild fall weather. Though autumn temps were warmer than typical, they were still somewhat cool and it showed in the 2024 gas bill (~$0.60/Therm).


I've got a brand-new solar cover that's been sitting in the box for a few years. If we're going to keep doing this late-season stuff, it might be time to finally install the cover on the reel and start using it.

 

[Newdude]

Heat pumps are not very popular here, I think due to the hot climate

Heat pumps prefer warmth and humidity. You got boat loads of each.

Many have built in spas by you and with 1/3 the BTUs they don't want to wait for the HP so they typically use gas heaters.

 

[djdonte]

Interesting points! My water is currently 76F, a little cold for swimming if you ask me. My pool gets sun the morning and lunchtime. It’s close to my two story house, so right during the hottest part of the day maybe 2ish, the sun starts to disappear behind the house.

I don’t want to do a heat pump. My 150 panel is getting close to its max and I would like to leave room for an EV charger. The gas meter is in close proximity to my pool pad, so I’d rather run gas line than a new circuit if I could avoid it. I will ask the folks I get quotes from about their opinion of heat pumps though. I just don’t see them often here.

 

[SJPoe]

Interesting points! My water is currently 76F, a little cold for swimming if you ask me. My pool gets sun the morning and lunchtime. It’s close to my two story house, so right during the hottest part of the day maybe 2ish, the sun starts to disappear behind the house.

I don’t want to do a heat pump. My 150 panel is getting close to its max and I would like to leave room for an EV charger. The gas meter is in close proximity to my pool pad, so I’d rather run gas line than a new circuit if I could avoid it. I will ask the folks I get quotes from about their opinion of heat pumps though. I just don’t see them often here.

Just to be clear, no one is saying you MUST get a heat pump - you've given at least two good reasons to go with the NG version anyway...it's really just a decision point that should get called out. Different folks have different priorities and needs.

With gas right near the pad, and other reasons why the electric route might be more problematic, a NG setup sounds like a good fit. NG is definitely more 'immediate', as much as these things are on 50 tons of water, but its also probably more expensive per degree of heating. YMWV

As for sizing, you're probably in the right ballpark - I have a 250kBTU on my 18x36, and have no issues maintaining temps throughout the season without getting a horror show in the mail from the Gas company.

 

[sande005]

My Minn. pool I referenced earlier will be getting a 266K btu heater as replacement - the same size as the old one. 18x36 pool also. BTU's are BTU's, so your pool will take a fixed number to get to, and stay at, a fixed temp for any given time period. The advantage to going big is that it can be warmed faster. So over time, small or large will give you the same gas bill. But the small may make you wait 12+ hrs (depending on the start/end temp) before you can swim, and the big may cut that wait time in half. So if you can upsize, without big expense, do it.