Vaillant AroTherm Plus 7kW

JamesPa · 2025-03-19T16:31:00Z

The Vaillant AroTherm Plus 7kW heat pump is a stylish, compact and highly capable unit that delivers efficient heating and hot water with a user-friendly control interface. While it operates whisper-quiet most of the time, it’s not without its flaws – most notably a noticeable increase in noise during defrost recovery. However, with its flexible settings, excellent tech support and cost-effective performance, it’s a strong contender for those looking to transition to renewable heating. Introduction and Background This review focuses on the Vaillant Arotherm Plus VZW 75/6, commonly referred to as the ‘7kW’ model. The unit was installed in November 2024 in a 1930s detached house with approximately 200 square meters of floor area. It replaced a condensing gas boiler dating from around 2007. The house originally had solid walls and metal-framed windows, which remain in some areas. Two modest modern extensions, partial internal wall insulation, 300mm of loft insulation, and mostly UPVC replacement double glazing have improved the insulation, earning the property an EPC rating of ‘C’. Two full fabric surveys (one free and one paid for, each taking three hours) calculated a heat loss of 16kW at -2°C. Other estimates, without a full survey, ranged from just under 7kW to 16kW. Analysis of gas consumption suggested a heat loss in the region of 6-9kW. A closer examination of one of the full surveys revealed that many of the fabric upgrades had been ignored, and some losses were double-counted. Correcting for these errors, while using standard MCS assumptions, reduced the calculated heat loss to 10.5kW. During this period, several quotes were sought, ranging from £12,000 to over £20,000 before applying the Boiler Upgrade Scheme (BUS) grant. A delay allowed for a more accurate determination of heat loss based on gas consumption, confirming beyond reasonable doubt that a 7kW unit would suffice. To account for the discrepancy between ‘measured’ and ‘calculated’ heat loss using MCS defaults, it was necessary to assume an air change rate of 0.5 per hour (as opposed to the default 2-3). Anecdotally, some suggest this lower figure is more reasonable in many cases. The delay also provided time to better understand the technology, with the help of the Renewable Heating Hub and other resources. By the time updated quotes were sought, it was clear what was needed: a 7-9kW machine directly connected to the central heating system without an intervening buffer, low-loss header (LLH), or plate heat exchanger (PHE) – essentially, no ‘system separation.’ A new unvented cylinder was also required. Only four radiator upgrades (including one fan coil) were necessary, as seven had already been upgraded during earlier phases of the work. A 16A dedicated electrical feed was already in place. Height constraints (the unit had to fit under a window) narrowed the choice of models, and noise requirements eliminated several manufacturers. The published specification for the Vaillant ‘7kW’ model indicates an output of approximately 8.5kW under design conditions, though there are unverified suggestions that this figure does not account for defrost cycles and should be downrated. Its relatively compact size and appearance made it particularly attractive, and several installers recommended it. Additionally, Vaillant’s pre-sales tech support had been prompt and helpful, addressing all my queries. A provisional decision was made to proceed with this unit. Vaillant was contacted again and provided contact details for three local installers. These installers were given evidence of the measured heat loss, a clear brief that any proposal involving system separation would not be accepted, and other relevant material. A particularly impressive installer identified during the initial work was also asked to confirm their earlier quote. All installers were bound by MCS rules to conduct their own heat loss assessments, but their willingness to consider the provided evidence varied. Ultimately, the choice came down to two installers, and a scoring system was used to make the final decision. The local installer won, primarily due to their proximity. The Installation The installation took six days in total, with a single installer completing the entire job. He worked nine-hour days or longer, often without breaks, and was frequently offered tea and biscuits! On one occasion, he stayed until 9 pm to finish fitting and connecting the DHW cylinder, which proved tricky due to the complexity and age of the existing plumbing. The installation was neat and well-executed. The installer programmed a fairly conservative set of parameters and provided a brief overview of how to adjust the ‘user’ settings. I suspect he deduced from our conversations during the installation process that I was reasonably familiar with the technology. Both before and after the installation, Vaillant contacted me several times to check on progress and ensure everything was running smoothly. This le...

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JamesPa

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Topic starter 24/06/2025 2:09 pm

Posted by: @scalextrix

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@judith we had a thermostat fitted for the kitchen as there is a lot of solar gain, and it seems to have stopped that function.

I'm not really bothered though.

If the thermostat is connected to the call for heat terminal on the vaillant or myson then I suspect it's also a call for cool (IE an 'enable'). If you turn it to max it will probably override.

This post was modified 4 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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