What we did to get our air source heat pump working efficiently

by Mars

This winter was telling for our air source heat pump, especially after a bitterly cold spell in February, and the main area of concern was that the rooms to the north of the house were not getting to temperature.

We got in touch with Global Energy Systems (the manufactures of our air source heat pump) to discuss this issues. We worked with them to come up with a solution, and we are very pleased to say that we think that we have finally got our central heating working effectively. We fitted a bigger circulation pump and upgraded five radiators with Stelrad Compact K3s (full review coming soon).


Steffan 23 April 2021 - 09:27

Glad to hear you have upgraded your rads. With low temp heating you can’t get enough radiator surface area!
Now in the spring the sun has been wonderful and its raised ground temperatures and average air temp for the day, so your heating requirements will have dropped a lot. Hopefully your upgrades will see you more comfortable next Winter when temperatures get cold again.

Mars 23 April 2021 - 09:44

Thank you for your feedback Steffan. The new K3 radiators from Stelrad are amazing and we have a newfound appreciation for the importance of radiators in low temperature heating systems such as ours.

We have still had a few extremely cold nights, and looking at the data from the Eve Thermo units, the rooms have remained at temperature and are significantly warmer. As you have said though, the true test will be next winter, but I feel like we’re far better equipped for it now.

Stephen Durrant 23 April 2021 - 10:29

Did you have any ice problems on your heat pump and a long cycle time for defrost and a lack of heat.
Our pump was iced up for most of the night and it did not melt until the afternoon. When it’s iced up, no air can go into the heat exchanger and provide room temperature

Mars 23 April 2021 - 10:32

We’ve never really experienced too many issues with defrost cycles. During the cold months, when humidity is high, we would ice over, but defrosts typically take 2-3 minutes and we’re back up and running. This has never been a factor. We’ve had other issues that related to flow to the north of the house and with the filter. This has all been addressed as part of the latest work.

Where did you heat pump ice up? On the fan or on the evaporator?

NormanB 23 April 2021 - 10:52

Mars, I am very pleased to learn you have resolved some of the issues with your heating system and reassuring that Global has supported you in achieving resolution. I cannot tell how much I have been waiting for this update – patiently.😉

From your description in the YT video however I do not think this is the end game. I will email you separately.


Mars 23 April 2021 - 12:26

Looking forward to the email as always 😀

Susan Ballard 23 April 2021 - 12:16

We’ve been waiting with bated breath for episode 9 to hear how you resolved your issues. Like you we moved into our dream house in Feb this year but want to update the heating system from a 25 year old (sic) dirty oil boiler to a renewable technology. ASHP is our preferred solution so we’re avid learners from your experience. Thank you so much for sharing.

Mars 23 April 2021 - 12:25

Thanks Susan. The K3 rads from Stelrad are nothing short of amazing, and should be definitely be considered because they’ve made a huge difference.

What pump are you considering going with?

anna+mycoe 23 April 2021 - 14:51

Hi Mars
Glad your happy with the results ! Though
During the survey a d design stage the heat loss of the rooms in question should have been worked out a nd the system designed accordingly, and the installation of K3 rads is not uncommon to achieve the surface area needed. Not sure weather you had a full system revamp or a new installation at the out set, but if it was the latter I would suggest that the upgrades you have had shouldn’t be at your cost, as that seems like an initial design flaw.
Happy to hear you have It sorted though

Mars 23 April 2021 - 21:46

Thanks Anna. Some very acute observations, and I’d rather not focus on the ‘short fallings’ of the initial heat loss calculation and heat emitter guide which we’ll diplomatically put down as human error on the part of the sales person. Global Energy Systems have been excellent throughout this process and took responsibility, and the system amendments were not charged for. We’re just happy that our heating seems to be more balanced now and that we’re successfully heating the rooms at the north end of the house. The K3 rads have been a game changer, and we’ll consider putting in a few more in strategic rooms where they’re needed. The true test, however, will next winter.

David 25 April 2021 - 09:26

You would think that Global energy would have sized your rads correctly in the first place to be fair.Its great that they came out though.

On another note regarding heat pump companies and my experiences. I have had x3 companies come out to do a survey, including Global Energy and all three have come back with a different sized heat pump ranging from 8kw to 14kw. I don’t kniw how I can possinly go forward to be honest.

Andrew Thornton 4 May 2021 - 14:30

Interesting information as ever – thank you. As newbies to ASHP – installed in December 2020 – this has been a strange time. We had three quotes – one said replace all radiators and the other two said replace six or seven. We chose the six with an 11.2KWh Mitsubishi and retained our oil burn Aga – which I’m glad we did. We have a persistently cold hall struggles to get up to 18* in winter and our bedroom is cold too – both of which have their original radiators. We have no underfloor heating and a large house. The house has never been cosy since ASHP so I am taking from this that I should get the installers back. Incidentally, in an attempt to keep the house warmer I keep the thermostat in the hall as this is the coldest – is this the right thing to do? I don’t think the hall has ever reached 20 in winter and therefore feels cold. As the weather brightens it becomes less of an issue but I’m not looking forward to next winter. Oh and by the way, the old timber frame double glazing that was in has been replaced throughout by modern units – but still cold spots as before.

ken B 11 July 2021 - 13:20

“We have a persistently cold hall struggles to get up to 18* in winter and our bedroom is cold too – both of which have their original radiators.” Does that not say it all. As a rule of thumb all rads should be doubled in size but people think they can get away from it and then blame the hp.

And dont talk about oil filled AGAs !

According to fuel consumption figures published by Aga, a four-oven oil-fired cooker-only Aga consumes about 2,650 litres of oil each year if used as the sole cooking device. At 45p/litre this costs over £1190 per year. This is nearly 33 times the UK annual average amount of energy used for household cooking.

andrew thornton 12 July 2021 - 11:41

Well that was a useful contribution to my questions – thank you! Not!!
We took the advice of the installation company not to replace all the radiators and assumed that they knew what they were doing.
For the record, we anticipate oil consumption of 810 litres this year …
To be honest – I thought this blog would provide some helpful insights into the issues you raised Mars…


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