Can a heat pump water heater supply more than one shower?
Can a heat pump water heater supply more than one shower? Yes, a heat pump water heater can indeed supply more than one shower, but it’s got to have enough stored capacity and a water supply system that can get the hot water to the right place, in the right amount of time. Provided the hot water cylinder has got enough room to hold the extra hot water and the property’s pipes can deliver the required flow rate, you’re in the clear. If two or more showers are going to be used one after the other, it’s all about the cylinder’s capacity and how quickly the heat pump can recover. If several showers are going to be running at the same time, you’ll also have to think about the available mains water pressure, flow rate and the pipework.
For a flat, apartment, smaller house or similar low-demand application, see our 100 litre compact wall mounted heat pump water heater.
For homes requiring a larger stored hot water volume, our options include the 200 litre domestic air source heat pump water heater and 300 litre domestic air source heat pump water heater.
For very large homes or commercial buildings, see the 400 litre commercial air source heat pump water heater or 500 litre commercial air source heat pump water heater.
How Much Hot Water Do Showers Use Up?
It all comes down to the flow rate of the shower and how long it stays on.
For example, an 8 litre per minute shower is going to use:
- 48 litres in 6 minutes
- 64 litres in 8 minutes
- 80 litres in 10 minutes
Two 10 minute showers at that flow rate would therefore use up around 160 litres of mixed water.
And don’t forget, higher flow showers can use even more. A 12 litre per minute shower running for 10 minutes will use around 120 litres.
So the number of showers alone isn’t enough to size a heat pump water heater; you also need to know the flow rates and how long they normally run for.
Does 160 Litres of Shower Water Need a 160 Litre Cylinder?
Not necessarily.
The water coming out of the shower is usually a mix of hot water from the cylinder and cold water from the mains.
Let’s say the cylinder is storing water at 60°C, the incoming cold water is 10°C and the shower temperature is 40°C.
Under those conditions, 160 litres of mixed shower water would theoretically need about 96 litres of stored hot water, with the rest coming from the cold mains.
Of course actual usable hot water will vary for a loads of reasons, including cylinder stratification, heat loss and changing water temperatures as the cylinder gets drawn down. But this gives you an idea of why the nominal cylinder volume is not the same as the amount of shower water you can get out of it.
Can Two Showers Run at the Same Time?
Yes, potentially, particularly if you’ve got an unvented heat pump water heater connected straight to the mains water supply.
But the heat pump itself doesn’t determine how quickly water can leave the cylinder.
If two showers each need 10 litres per minute, the system needs to deliver around 20 litres per minute while they’re running together. And other outlets could increase that further.
The incoming mains supply, pressure reducing equipment, cylinder connections and distribution pipework all need to be up to the task of delivering the required flow.
A 300 litre cylinder doesn’t automatically mean you can run several high-flow showers at the same time if the incoming mains supply is rubbish.
What if the Showers are Used One After Another?
In this situation, stored hot water capacity becomes the main priority over simultaneous flow rate.
For example, a family might have four people showering one after the other in the morning.
The cylinder needs enough usable hot water to cover that period of peak domestic hot water demand without running out before everyone’s finished.
The heat pump may also be heating the cylinder during this period, but it’s generally better not to rely on it to recover quickly to compensate for an undersized cylinder.
How Fast Does a Heat Pump Water Heater Recover?
Recovery time varies between models.
An air source heat pump water heater will generally reheat stored water more slowly than a high-output boiler. The actual recovery time depends on the heat pump’s heating capacity, cylinder volume, incoming water temperature, air temperature and target hot water temperature.
This makes getting the right cylinder size even more important in homes with several bathrooms.
A larger household may need enough stored water to cover the morning shower period, with the heat pump then recovering the cylinder gradually afterwards.
Would a Larger Cylinder be Better for Multiple Showers?
Often, but it should still be sized to the actual demand.
A household with one low-flow shower may be perfectly happy with a relatively modest cylinder. A property with two bathrooms, rainfall showers and several occupants may need a whole lot more storage.
Larger cylinders can give you a greater reserve of hot water, but they also take up more space, cost more and may have higher total standing heat losses.
The aim is to provide enough stored hot water for the busiest time without unnecessarily over-sizing the system.
Does Storing Water at a Higher Temperature Help?
Yes, it does. Hotter stored water can be mixed with a greater proportion of cold water, increasing the amount of usable shower water you can get out of the cylinder.
However, higher temperatures can reduce the heat pump’s coefficient of performance and increase standing heat losses.
Getting the right cylinder size is usually a better bet than continually running at an unnecessarily high temperature just to compensate for not enough storage.
Will the Immersion Heater Help?
Most integrated heat pump water heaters come with an electric immersion heater for backup or boost operation.
This can give you a bit of extra heating during periods of unusually high demand, but it shouldn’t be required every time several people take showers. Frequent use of your immersion heater will see your electricity consumption shoot up, and that can be a pretty clear sign that your cylinder is too small, or the heat pump is struggling to keep up, or maybe your control settings just aren’t that finely tuned to the household.
How do I size a heat pump water heater for when the whole household is using the showers at the same time?
First, you need to get a grip on just how often and for how long the showers are going to be running. That means knowing the shower flow rate, how long the average shower is going to last, and just how many showers you can realistically expect all at the same time. And if showers are going to be running at the same time, you should also check what the mains water pressure and flow rate are like.
When you’re talking about a house with loads of bathrooms, you’ve got to take all of this into account: cylinder size, the usable volume of mixed water, how hot the stored water is, shower flow rates, peak demand and how quickly the heat pump can recover.
A heat pump water heater that’s the right size should be able to handle the lot – but the key is having enough energy stored up for when the house is at its busiest and, at the same time, having a water supply that can deliver the flow needed to keep all those showers going.