When I was at college I was awful at maths, and I failed my A levels twice. At fridge college I found it much easier because the teachers were able to explain to me what we were actually trying to work out, so I found getting to the answer much easier. I’ve since discovered that most of our customers are great at getting things installed, but they don’t relish doing mindless maths. So my aim is to reduce the tedium and get answers without having to get the calculator out.

In the world of heat pumps we do hundreds of simple calculations to work out heat loss, pipe sizes, cylinder recovery times, etc. The maths isn’t hard but it’s repetitive and tedious. It dawned on me that it would be a good idea to set the results out in a table to give us a quick idea of where we are going with minimal work. For all the purists out there, don’t panic, we will still always do a full calculation for you but it’s a good idea to see where heat pumps work best and avoid having to do a survey on a property where a heat pump makes little or no sense.

The table below gives you an immediate idea of what the heat load will be for houses of different ages and floor sizes. For example, a 150m^2 1930s house will have a heat loss of about 13.5kW if it hasn’t had significant insulation modifications since it was built, like double glazing, loft insulation and cavity wall insulation.

Next, I worked out how much carbon you would save if you switched from a gas boiler to a heat pump. Many customers really like this sort of information because they can see how much impact they can make to their family’s carbon footprint.

And then I did the big one: how much money would the heat pump save you versus gas.

I also did this exercise for oil, but I’m trying to keep this post brief.

OK. If you now factor in the RHI grant and the installation costs we can look at how many years it will take to pay back the homeowner for going down the heat pump route versus running a gas system.

In this calculation all I did was take the total cost of a heat pump installation, minus the cost of a gas boiler installation. I’ve assumed you would only consider fitting a heat pump if you were going to replace your boiler and that the boiler would cost £3,000 installed.

Now that I have the difference in the cost of the two systems all I did was work out how long to run the cost savings along with the grant and how long it would take to pay back the difference. I used the kit I’m most familiar with and stopped when we couldn’t cover the load with a maximum of two units or 20kW.

And here it is. Note how the houses in blue pay back the quickest. The yellow areas are next and the green last. The red areas are hard work and they are just a bit too big for a single heat pump.

Using this table you can see really quickly if your house would benefit from a heat pump and use this quick guide to see the houses where you are potentially not going to benefit as much. This should make it easier to decide if going to survey makes sense. This is just a guide though. Remember that.

## 1 comment

Thank you, very helpful, I can almost understand the tables.

This rural village does not have a gas supply, so the majority are using oil for heating. I note that there are tables for oil, I would be grateful if I could have sight of these. I need all the evidence I can get to convince a sceptical wife.

Thanks.