Gas boiler vs Heatpump
Tom: If we just look at a straight comparison between a gas boiler versus heat pump (for heating) on their own merit - there's a shorter term and a more medium term view to how I usually like to frame this conversation.
So your actual mechanics of how they work:
A modern gas boiler - you're looking at 95% efficiency which means if you put one unit of gas into it, there'll a five percent loss in the move from that being gas to actually creating the heat through the system.
And then a heat pump, because of the way it uses the the air from outside and then the refrigerants within the unit (they're improving all the time) - but generally a well-designed system is anywhere between 350 - 400%. So that means if you put one unit of electricity through the heat pump, you'll receive between 3.5 and 4 units of heat.
That's why, if you look at gas at 7p and electric at 25p you think:
'well how can they be similar to run when the cost per unit is so different'
It's because of what you call a SCOP which is a coefficient (Seasonal Coefficient of Performance) and that gives you a rating of how efficient a heat pump is across the whole year.
So looking at it on its own, if you can get the heat pump to be 3.5 to 4 times as efficient as a boiler, but then the fuel cost difference is about 3 - 3.5 times between gas and electric. it doesn't stack on its own at the moment.
It will come down to how low we run the flow temperature of the heat pump.
The more you bring the flow temperature down, the higher the efficiency gets because you're not having to heat the water to such a high level.
In a boiler, traditionally, the flow temperature will be about 70 degrees celsius. In a heat pump you can run it as low as 35 degrees so obviously when you're trying to get water up to 35, rather than up to 70, it's going to use less energy.
The caveat with that is, the lower you bring the flow temperature of a heat pump, the bigger the radiators get. So there's always a middle ground between how low can we bring the flow, without the radiators becoming the size of the whole building!
Generally you'll find that most retrofit systems will run between 40 and 50 degrees, and that's kind of your sweet spot where you can make the heat pump similar or slightly cheaper to run than gas.
This is if we're comparing the heat pump to a new boiler.
If we're looking at a boiler that's already been in for 10, 15, 20 years and they haven't got the right heating controls, and if that boiler is running at sub 80% or 75% efficiency - you know it's either on or it's off, and people in offices are saying:
'oh once the heating's on it's just boiling in here and we can't do anything about it'
You've got an inefficient system...
All of sudden, you're comparing 3.5 to 1 on the prices, to a difference of like 5 - 5.5 to 1 on the efficiency of the boiler and heat pump.