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Isoenergy has been installing heat pump systems for clients for over 10 years. We have had countless conversations with homeowners who have heard that the temperature of the hot water out of a heat pump is lower than a fossil fuel boiler. We are most commonly asked the question “What about the dishes? Will the hot water be hot enough for us?”

Conventional plumbing and heating engineers are used to installing fossil fuel boilers which generally output temperatures in the region of 60 – 70°C. In their view, anything that outputs a lower temperature is inadequate for producing domestic hot water. This is simply not the case.

Gone are the days when heat pumps were limited to an output temperature of 45°C. Most quality heat pumps will provide 55°C with ease and some higher temperature units can produce as high as 70°C (at a reduced efficiency of course).  55°C is certainly hot enough for domestic use and in fact most hotels and care homes limit the temperature of the hot water at the tap by adding cold water to the mix. The resulting temperature is usually just below 48°C as specified in the Building Regulations.

We have heard plenty of other arguments claiming why a fossil fuel boiler is better for hot water than a heat pump. Here are some of the most common:

Can I still have a steaming hot bath?

When running a bath we would normally add both hot and cold water to the mix to get the right temperature. Bathing in 60°Cwater straight out of the tap will cause severe scalding. The Department of Health recommends temperatures no higher than 43°C for bathing and 41°C for showering.  It is true that with a heat pump, the water coming out the tap is cooler than the water you can get out of a fossil fuel boiler, but by adding more hot water and mixing in less cold, the same desired bath temperature can be obtained. This does mean that you will need a larger store of hot water and isoenergy will normally replace your existing water tank with a bigger one for this reason.

The water in the tank may be hot, but it is cold by the time it reaches the bathroom at the other end of the house.

To address this, isoenergy recommends insulating any hot water distribution pipes where possible. Of course, sometimes these pipes are not accessible and so we can specify a heat pump with a higher output temperature. It is worth stressing, that this has not been necessary in the vast majority of systems we have installed.

But what about Legionella?

In the UK there is regulation in place saying that hot water storage must be protected against the growth of harmful bacteria, such as Legionella. All well-designed systems will have an immersion heater in the hot water tank that can be used once a week to pasteurise the water. For isoenergy installations this is set on a timer, usually once a week at 2am when the immersion switches on and the tank is held at over 60°C for more than an hour. This pasteurisation keeps the water safe for you and your family.

But what about the dishes?

And yes, the hot water that comes out of the kitchen tap is hot enough to clean the grease and grime off those pots and pans, so there goes your excuse for not doing the dishes.

For more information on how a ground source heat pump or air source heat pump can replace your current fossil fuel boiler, get in touch or call us on 01293 821 345.