I'm learning about heat pumps the hard way - now you don't have to.

I get asked this question so often. Media constantly bad mouths heat pumps:

·      You’ll be cold in your home

·      They make too much noise

·      They cost a fortune to run

·      The neighbours will complain

·      You need a massive amount of space in your garden

They are like Marmite – people love them or hate them – and those that speak loudest ove to hate them.

This is our fifth year with a heat pump and I’m learned a great deal. But don’t worry – I’m going to share it all so you don’t have to go through the process yourself.

What are the problems with a heat pump?

 

1.     Installers are not well enough informed or experienced enough to get the installation and set up right. Read more about this here

2.     Homeowners don’t understand from the outset how heat pumps work, so they carry on using it like a gas boiler. Read more about this here

We’ve been caught by both of these problems

Thanks to great customer feedback on the Everything Electric YouTube video about our home, I discovered that we were using the pump incorrectly. It had just never entered our consciousness that we might be doing it wrong.

Informing customers about this is an important part of the handover. I don’t recall being told this, but then we were taking in so much in one go that we could easily have missed it. So I’m not blaming – just realising that understanding how the pump functions needs to take pride of place before the installer leaves.

So what are we doing about it

If you’re following my blog then you know that I’m a retrofit junkie – I find it totally fascinating in its own right, but also a marvellous contribution to healing the planet and leaving a workable world for all the grandkids. So there is no way we were going to carry on as before.

This was a fascinating challenge, so I set about exploring. And I found a Heat Geek installer who was up for finding out more with us and making any changes that are needed. Not easy to do – most installers don’t like adjusting someone else’s work. Totally understand that but I guess there will be increasing amounts of work out there for exactly that soon.

First question – is the heat calculation correct?

The installer was at a disadvantage with us. We’d taken on to retrofit throughout, but we were learning on the job. We had the blueprint of the extension which had been designed by an eco-architect plus any information I could find on the web. So not sure how clear our summary of the planned work would be. I also think we ended up doing better than we expected. So pretty hard to do an accurate heat calculation from that.

The first recommendation was for a 12.5Kw heat pump. John was very sure this was too big. The insulation and airtightness we were aiming would be better than that implied.

After much conversation and recalculating it was agreed that we could have an 8.5kw pump. This is now in situ and working well. Except the suggestion that we could get an even better energy reduction than our existing 75%.

Why does the size of pump matter?

The most costly part of running a heat pump is when it switches on and off (cycling). It’s at its most efficient when it can just keep running. It also heats your home more evenly – when it’s cycling, you can end up with warm and cold spots. Not to mention the extra cost for a bigger machine.

Right sizing your heat pump is significant in terms of energy saving – too large or too small it will have to work harder. Right size and it can plod on gentle leaving you warm, comfortable and better off.

Installers err on the ‘safe side’

Gas boilers can be oversized without any downside – except possible for purchase cost. Because it runs at a higher temperature – over 60 degrees, it can go on and off without much impact on the home and without having to work so hard.

Because many heat pump installers have previously been gas fitter, they tend to err on the side of caution - make it a bit bigger to be on the safe side - without taking into account the extra expense of running it.

Our first step – redo the heat calculation

So this is where we’re starting with the rejig of our system – redo the heat calculation. Having given over all the insulation information, the first pass suggests we actually needed a 4.5 kw pump. B****y hell!

A Heat Geek has been in to do the next stage of the assessment – looking at the pump itself, the set up, our radiators, ventilation…..

Next step - redo the blow test

We are also having a second blow test done to re-evaluate our airtightness, so that information can be added to the calculation. The first one was dire, but helped us realise a few places we’d forgotten. It’s never going to be as good as we’d like – we didn’t know enough at the right time – but hopefully it will be better now we’ve done some retrofitting of the retrofit.

More about that in the next blog.

If all this makes you think: ‘I need to understand more about this retrofit business before I make decisions I’ll regret, then take a look at my book: What the Builder Won’t Tell You.