One of our most frequently asked question, answered!

The question of whether an instantaneous water heater can fill a bath is certainly one of the most popular questions we get (daily!) regarding water heating.

If you are looking for a way to heat water quickly and efficiently for your bath, you might be wondering if an electrical instantaneous heater can do the job. An electrical instantaneous heater, also known as a tankless or inline water heater, is a device that heats water as it flows through it, without storing any hot water in a tank. This means that it only uses electricity when you need hot water, and it can provide a continuous supply of hot water at the point of use.

This type of water heater has many advantages, including the compactness and efficiency (as you only ever heat the water you use rather than keep a quantity of water hot in case you need it).

Unfortunately this style of heater does have a few drawbacks however, including the high kW needed to get sufficient heat into the passing water, but in the case of filling a large vessel such as a bath, the main issue is the capability to deliver fast flowing hot water. The most powerful instantaneous water heater for a domestic setting (single phase electricity) would be around 12kW (50A). This would be capable of providing around 5L per minute of water at a typical bathing temperature of 38 - 40 degrees Celsius. So, if we look at the required amount of water at this sort of temperature for an average sized bath containing an average sized adult, it is around 100L.

The maths is pretty simple: it would take around 20 minutes to get to 100L using this most powerful of water heaters. Of course, during this time the water that has already been heated will have cooled down a fair bit, depending on ambient temperature. For that reason, we are confident that an instantaneous water heater is far from ideal to fill a bath.

The above scenario is based on the Zip DEX12 water heater, and although Zip claim the unit is suitable to fill a bath, we disagree for the reasons stated and don’t recommend it for that purpose, good though it is for many other applications.

If you’d like to know about a water heater better suited for the purpose of filling a bath, you could do a lot worse than to have a look at the Hyco Powerflow 80L or 100L or the Heatrae Sadia Hotflo 80L. Both neat looking wall hung water heaters rather than big ugly cylinders!

 

If you’d like to enquire further, or need a little more help choosing the right heater for you - instantaneous or otherwise -  please call our friendly water heating geeks on 01934 253600.