Running Two Aqualisa Showers Simultaneously

5 Jan 2015
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United Kingdom

I have purchased two Aqualisa Quartz Gravity Pumped showers (older version).


Within the instructions it reads the following, “The capacity of the hot water cylinder must be capable of meeting anticipated demand” (note, it also says this exact same line in their new line of showers).

What I'd like to know is what does this mean? We want to be able to run both showers simultaneously, so would this mean we need to have a hot water cylinder of a certain size? Is there a calculation or answer for this?

Lastly would there be any flow problems from running both showers simultaneously?

Many Thanks
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Let's suppose that each pumped shower delivers ten litres of water per minute.

Suppose that your water store is 100 litres.

One pump will exhaust it in ten minutes.

Two pumps will exhaust it in five minutes.

Depending on the layout and size of your pipes, yes, it is likely that you will get reduced flow if you try to use them both at the same time. You may also get air in the pipes if the pumps try to suck more water than is available.
Hi JohnD,

Where are you getting these figures from? Obviously I know how those simplee maths working, I'm more wondering what standards would be common in the UK. My house was built in 1985.
They're guesses, but not too far removed from reality.

As you have pumped showers, I guess that you have a vented cylinder. These are often around 125 litres of which maybe 100 litres will be hot when you start your shower (in fact you will also use some cold, but if you have an unvented cylinder, the cold tank in the loft might be around the same size and you will be draining it faster than it can refill, and when it is drained, neither the hot nor the cold taps will work). As it is a vented cylinder it will probably take more than half an hour to reheat once cold.

If you look at your cylinder and tank, you may find the capacity is on a label. Or it can be estimated if you give the dimensions.

10lpm is considered adequate for a shower in the UK. Some people have as much as 20lpm, which is very good for the UK. As you're going for pumped showers I guess you prefer a good flow.

If your house was built in 1985 there's a chance it will have a plastic incoming waterpipe of decent size, and you might in future consider upgrading to an unvented cylinder. These run at higher pressure and are usually much larger, so a better solution for powerful showers. They also reheat faster, if you have a fairly powerful boiler. It's a more expensive job, though.
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My house was built in 1985.

And from that, you think we can deduce your DHW delivery capabilities? Wish I could, I'd be rich! :LOL:

You need to measure your CWSC and your HWC and pipe sizes connecting each and calculate how much hot water you have available when cylinder is up to temp.

Then do some calcs using the output specs of the shower pumps to work out how many minutes it would take for both the pumps to deplete the stored hot water. If both pumps are fed off the same flange on the cylinder, you could also end up sucking air into the draw off.

Either way its as simple as how long it will take to deplete your volume of hot water.

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