# Shower: water heat transferred to room air

How much heat from a shower goes to heating the room?
We have a 9.5 KW walk-in shower and it heats up a chilly bathroom without the need to switch on the 2kW wall heater.
I was wondering how much heat typically gets transferred from the hot shower water to the room air?
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On 14/11/2017 00:35, pamela wrote:

You will need a thermometer, stopwatch and measuring container to arrive at a result.
Power lost into room (kW) = (flow rate (l/min) * temp drop(shower head to plug hole (deg C)) / 14
Andy
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On 13:38 14 Nov 2017, Andy Bennet wrote:

I hoped this had been worked out before for an average shower giving a rule of thumb which might have said a quarter (or whatever) of the heat gets passed to the air.
The sort of statistic which might find its way into the newspaper or get quoted, although I hadn't heard it.
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On 14/11/2017 15:51, pamela wrote:

As you can see from the formula I provided, the shower/room heat transfer is determined by the shower flow rate and the temperature loss in the shower stream.
The temperature change in the room will, in addition to the power transfer to the air by the shower, be a function of room air volume, the current air temperature, and any additional cooling/air change in the room.
Unfortunatly there will not be an average answer due to the variables involved in each installation.
But I think I answered your original question about "how much heat typically gets transferred from the hot shower water to the room air".
Andy
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On 14/11/2017 15:51, pamela wrote:

The short answer is that the loss to the air is negligible when comared to the energy that went into heating the water - certainly not a quarter - or even a tenth of that.
You are using a flow of water (lots of it with a high energy density), to heat small amount of air with a low energy density.

That's because when you do the sums, its not really significant, and ultimately not really that important.
You pay the money to heat the house, you can do that by heating water and pumping it round some radiators, and by squirting it out of a shower head in direct contact with the air. One can argue that the shower heating the room is a bonus from a comfort point of view, even if not from a condensation one.
--
Cheers,

John.
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On 14/11/2017 15:51, pamela wrote:

I am sure the Express could make it's own figures up if it needed a report on such a thing:-)
--

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On 19:31 15 Nov 2017, ARW wrote:

Yes, I'm sure of that too!
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On 13:38 14 Nov 2017, Andy Bennet wrote:

This seems a good approach but the water will have lost heat to the shower floor before it gets to the plug-hole. As it's a walk-in shower there's quite a bit of shower floor that gets wet.
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On 14/11/2017 00:35, pamela wrote:

You already have enough information. If it warms it up as effectively as a 2 kW heater, it is 2 kW.
There is no *general* answer because it depends on too many parameters, not least the flow-rate of any extractor fan.
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On 14:14 14 Nov 2017, newshound wrote:

It's not identical to a 2kW fan heater but it replaces the need to put the fan heater on - in some circumstances.
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On 14/11/2017 15:49, pamela wrote:

OK, well if it heats the room up half as quickly as the heater, then it is giving you 1 kW.
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I find the best combination is to run a dehumidifier in the room whilst having a shower. The room gets nice and toasty, and I can shave afterwards as the mirror doesn't fog up.
My dehumidifier is a condenser type that draws about 200w. But the effect in a shower room seems much more than that, so I guess there's quite a bit of heat coming from condensing the water vapour.
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On 14/11/17 17:46, Caecilius wrote:

50W/sq m is a very reasonable heat input to a resnonabley well insulated room
--
"Corbyn talks about equality, justice, opportunity, health care, peace,
community, compassion, investment, security, housing...."
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On 14/11/2017 18:51, The Natural Philosopher wrote:

Not sure of the maths here, other than to say from experience it would be enough to maintain a comfortable temperature in an already warm room. But pretty useless at warming a cold room.
--
Cheers, Rob

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On 14/11/17 19:32, RJH wrote:

Rubbish. My whole house had less than that overall
--
In todays liberal progressive conflict-free education system, everyone
gets full Marx.
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I did some calculations a while back, when I was thinking about putting a heat exchanger/extractor fan in the bathroom - if I calculated correctly, and recall correctly, most of the energy will be in the water in the air, rather than the air itself. So I stuck with the dehumidifier. I did make some rather off the cuff assumptions about the amount of water in the air, though - something like comparing the heat capacity of a litre or so of water to the heat capacity of a bathroom-full of air.
#Paul
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On 14/11/2017 00:35, pamela wrote:

In spite of various eminent contributions, I still think it is a pretty daft calculation, especially if you have an extractor fan. Hot water comes out of the shower, some of it evaporates (stealing a lot of energy as latent heat). You extract this vapour which then dumps the energy into the plume outside.
Of course you get it back if you run a dehumidifier inside, or if it condenses on the walls and ceiling.
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