# Swimming pool heating problem

#### lauraaa

I need to work out the most cost effective way to maintain a swimming pool in a UK holiday complex that is closing for 1 month in January and hope that someone can help.

I would like to know if it would be cheaper to turn off the heating system for a month and then reheat it from base temperature or keep the heating on.

The pool is 10m x4m and is 1.4m deep
The ambient air temperature can be kept at 20 degrees Celsius but this could also be turned off.
The pool and the air is heated by an oil boiler

So I guess the question is in principle does it use less energy to allow the temperature to drop all the way and then heat it up rather than to just maintain it.

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#### Nugatory

Mentor
So I guess the question is in principle does it use less energy to allow the temperature to drop all the way and then heat it up rather than to just maintain it.
There's no single answer "in principle".

How much fuel is burned in a typical month keeping the pool heated? You're going to compare that number with a back-of-the-envelope calculation of how much fuel would be burned to reheat the pool.

#### lauraaa

Ok, so I would need to know what temperature the pool would drop to. Do you know if it would drop to the ambient air temperature or could it get colder? Thanks

#### Chestermiller

Mentor
Suppose the time interval were 100 years instead of 1 month. What would your answer to that be?

Chet

#### russ_watters

Mentor
Actually, guys, since the OP doesn't ask "how much", only "which is more" (edit: or, at least, that's the bottom line question), there IS an easy, in principle answer to the question:

You use more energy maintaining a constant temperature because the heat loss is proportional to temperature difference. So as the pool cools, the heat loss rate drops.

Last edited:

#### mathman

Warning - if the water freezes you are in trouble.

#### Nugatory

Mentor
Actually, guys, since the OP doesn't ask "how much", only "which is more" (edit: or, at least, that's the bottom line question), there IS an easy, in principle answer to the question:

You use more energy maintaining a constant temperature because the heat loss is proportional to temperature difference. So as the pool cools, the heat loss rate drops.
Hmmm - yes - you're right. To minimize the energy consumption, the winning strategy is to stop heating the pool any time that it's not required to be at its operational temperature and heat it back to that temperature whenever it is needed.

That does mean that sometimes the pool will be unavailable while it's warming up, and the important piece of information that we need is: What is the cost (lost revenue, angry customers) of that period of unavailability? That can range from zero (scheduled shutdown during the off-season, reheating complete when the doors open for the new season) to very high. In this case, OP has already told us that it's a scheduled off-season shutdown so it's easy.

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