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6 Red Flags to Avoid When Considering a Heat Pump Installation

Simon Murray · 2024-08-27T20:25:25Z

As someone that's deeply involved in the design and installation of heating systems, I want to share essential advice for consumers considering an air source heat pump. My business partner, Luke, and I run Optimus Heating, and we’ve achieved recognition in the industry, winning Vaillant’s heat pump challenge last year and being one of 10 chosen projects in Viessmann’s Top of the SCOP’s competition. We specialise in creating highly efficient heating systems, often achieving efficiencies over 500%. This guide is not a pitch for business but a genuine attempt to help consumers navigate the misinformation surrounding heat pump installations. If you’re looking for a system with long-lasting efficiency, low running costs and minimal noise, here are the six red flags to avoid when considering a heat pump installation. Red Flag 1: Design Flow Temperature If you’re being sold a heat pump with a flow temperature of 50C, be cautious. A higher flow temperature can limit the efficiency of your heat pump and shorten its lifespan. Some manufacturers offer a 7-year warranty, which is far shorter than the potential lifespan of a heat pump installed with the correct parameters. The reason for this limited warranty is that manufacturers have no control over how the heat pump is installed, particularly concerning flow temperature. Many mass-market installations are designed for 50C flow temperatures, which can significantly reduce the lifespan of the compressor and increase noise levels. Additionally, for every degree increase in flow temperature, you may experience a 3% loss in efficiency. A heat pump designed with a 35C flow temperature can be up to 45% more efficient than one designed for 50C. Lowering the flow temperature naturally enhances efficiency, reduces running costs, extends the lifespan of your heat pump and minimises noise. Always question any company promoting flow temperatures above 45C. Red Flag 2: Rooms Designed at Different Temperatures CIBSE design guides recommend different temperatures for different rooms, such as 18C for kitchens and 21C for living rooms. However, designing emitters for varying temperatures in adjacent rooms can lead to inefficiencies. According to thermodynamics, heat will always move from hot to cold areas. This means that the warmer room will lose heat to the cooler room, causing your system to become unbalanced and your heat pump to work harder than necessary. It’s nearly impossible to maintain different temperatures in different rooms unless they’re vacuum-sealed. Your home should be designed with a single consistent temperature, with a setback temperature for cooler bedrooms overnight. Always question any company that doesn’t use one consistent design temperature across your property. Red Flag 3: Third Party Controls, Zoning & TRVs Imagine a simple two-up, two-down house, where each room has a 2.5kW heat loss/load, totalling 10kW for the entire house. If you install a 10kW heat pump and then zone the house into upstairs and downstairs, shutting off the upstairs zone during the day, you’ve essentially halved the water volume in the system. This reduction in water volume can cause your heat pump to cycle on and off, reducing efficiency and potentially shortening its lifespan. Heat pumps operate most efficiently when they can modulate their power to maintain a steady temperature. However, third party ‘smart’ heating controls often act like on/off switches, which can cause the compressor to cycle inefficiently. These controls were originally designed for combustion heating (boilers) and are not ideal for vapour compression heating (heat pumps). The best approach is to use weather compensation controls, which allow your heat pump to adjust its power output based on outdoor temperatures, maintaining a consistent indoor temperature without cycling the compressor. Always question any company that suggests using third party or ambient controls. Red Flag 4: Buffers, Hydronic Separation & Fixed Speed Circulation Pumps Buffers can be useful in some cases, but they’re often unnecessary for the vast majority of domestic UK housing stock. A buffer is essentially a cylinder of water connected to both the heat pump and the central heating system. In many cases, the use of a buffer with a fixed speed circulation pump can lead to inefficiencies, particularly when the pump doesn’t modulate according to the outdoor temperature. Most heat pumps are designed to operate with a temperature differential (ΔT) of 5C between the flow and return. However, when a buffer is used, the differential can become distorted, leading to the heat pump having to work harder to maintain the desired temperature. This can result in inefficiencies and increased wear and tear on the system. Buffers are often used by installers to simplify the installation process, but this can lead to a lazy and inefficient system. Instead, consider a volumiser, which can add system volume without the need for hydronic separation, allow...

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Air Source Heat Pumps (ASHPs)

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Mars

(@editor)

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30/11/2024 9:46 am

@jamespa it is a good idea, but not easy as you say. We actually have something along these lines scheduled in for recording next week Friday for the podcast.

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Clover Rayner

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30/11/2024 12:02 pm

This article highlights important factors to consider when installing a heat pump. Identifying red flags, such as poor sizing, improper installation, and lack of maintenance plans, ensures you avoid costly mistakes and achieve optimal system performance.

This post was modified 11 months ago by Mars

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Mike@MH

(@nogotony)

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30/11/2024 4:41 pm

Posted by: @gt22

↑

If I had a new ASHP installed I would still have to have a hot water cylinder. I watched the relevant video on this site. But I don't need any buffer unit.

Can I get clarification on this point.

Can the ASHP External unit, supply heat for Central Heating radiators or UFH at one temperature and one set of F&R pipes and do that supply directly? Bypassing the cylinder?

Or have I got that completely wrong and need to go away and do some serious reading? 🤔

This post was modified 12 months ago by Mike@MH

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JamesPa

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30/11/2024 6:15 pm

Posted by: @nogotony

↑

Posted by: @gt22

↑

If I had a new ASHP installed I would still have to have a hot water cylinder. I watched the relevant video on this site. But I don't need any buffer unit.

Can I get clarification on this point.

Can the ASHP External unit, supply heat for Central Heating radiators or UFH at one temperature and one set of F&R pipes and do that supply directly? Bypassing the cylinder?

Or have I got that completely wrong and need to go away and do some serious reading? 🤔

The ASHP, just like a boiler, can supply water at only one temperature at any time. So it switches between space heating and DHW. There will be one set of F&R from the heat pump, which splits into two sets at a diverter valve.

The reason that boilers (as we set them up in the UK) can do both simultaneously is that they run the heating at a high flow temperature, resulting in both reduced comfort and a 10% increase in energy consumption and therefore cost. Boilers, like heat pumps, are actually best run at a low temperature with weather compensation (best both for comfort and cost!), but in the UK we rarely do this, unlike some more enlightened countries in mainland Europe.

This post was modified 12 months ago by JamesPa

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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Alfapat

(@alfapat)

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19/01/2025 2:36 pm

Read your Red Flags with interest. Presently tweaking my system and getting the flow temperatures down as for the past 8 yrs It has been set at 50c
Currently adjusted lockshield valves to balance the Rads and brought the flow temps down to 44c without realising musch difference . I notice you suggest 38c which is quite low to what I have had it set but willing to try.

Can I ask what flow speed can my system run at , I notice there is a graduated glass viewing setting.

I also have a buffer tank in the system which I have only discovered from this forum may not be needed . However its there and reluctant to change , due to cost.

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