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The size of the Viessmann Vitocal 100-A air source heat pump depends on its output. (Image credit: Viessmann)

Introduced in 2020, the Vitocal 100-A air source heat pump was designed for ease of installation in the standard British heating system and is a good replacement for gas/oil boilers. It can help homeowners save money on their energy bills and reduce their carbon footprint.

As a monobloc unit, the Vitocal 100-A’s dimensions are ideal for a home where space is limited. The system does not require a complementary indoor unit. All components are incorporated into the outdoor unit, and manufacturers carefully considered the design to ensure it’s not an eyesore for homeowners.

You can choose from six output options depending on your home and energy needs: 6kW, 8kW, 10kW, 12kW, 14kW and 16kW. Units with the lowest output are smaller, and the 14–16kW option is the largest at 1,409mm (h) x 1,044mm (w) x 448mm (d), weighing 124.50kg. You can cascade up to seven units to increase output.

The Vitocal 100-A air source heat pump can also be installed with a Viessmann indoor combi cylinder, which combines a 250-litre heating water buffer cylinder and a 50-litre domestic hot water cylinder. Alternatively, you can use an outdoor plinth-style horizontal buffer store to save space inside your home.

The Vitocal 100-A air source heat pump can achieve 60°C when it’s as cold as –5°C outside, which would suit most homes in the UK. If the area you live in has colder temperatures, you may need to consider an alternative air source heat pump.

The unit has a high coefficient of performance of up to 4.9, which ensures a long service life. Due to its innovative heat exchanger, the Vitocal 100-A offers greater performance as it reduces defrosting time and provides corrosion resistance, which makes it a good solution for coastal homes.

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The Viessmann Vitocal 100-A is a fully integrated outdoor unit with a monobloc design, meaning a refrigerant certificate is not required by installers. 

There are six different output options: 6kW, 8kW, 10kW, 12kW, 14kW and 16kW . The 6–8kW model measures 828mm (h) x 924mm (w) x 377mm (d). The 10–12kW model measures 936mm (h) x 1,047mm (w) x 455mm (d). The 14–16kW model measures 1,409mm (h) x 1,044mm (w) x 448mm (d).

Units are designed for outdoor installation and contain gold-plated heat exchangers that are highly corrosion-resistant. 

The Viessmann Vitocal 100-A air source heat pump could be the right fit for you and your home, but you should be aware of the pros and cons before making a final decision. Here are the upsides and downsides of this particular unit.

The Viessmann Vitocal 100-A was designed to be compact and easy to install. (Image credit: Viessmann)

The Viessmann Vitocal 100-A uses a monobloc system where all components (apart from the hot water cylinder) are located inside the heat pump unit installed outside your home. It’s very quiet, thanks to its advanced acoustic design (AAD), making it ideal for urban homeowners.

It requires simple touchscreen operation and features a plain text display directly on the heat pump. This enables you to easily monitor and control your heat pump’s performance.

The Viessmann Vitocal 100-A absorbs natural energy from the air outside your home and converts it to be used in radiators or underfloor heating to warm your house or provide hot water. It works even if temperatures drop to –5°C.

Installing this unit and replacing a traditional oil or gas boiler can reduce your energy usage and carbon emissions.

Many other companies in the industry sell air source heat pumps with lower energy efficiency ratings than the Vitocal 100-A. However, if you live in a home with poor insulation or an extremely cold climate, you would be better off looking for a high-output air source heat pump like the Hitachi Yutaki S80.

The A+++-rated Hitachi Yutaki S80 air source heat pump offers outputs of 32kW, making it ideal for very large properties. It heats water up to 80°C even when it’s –20°C outside.

If you have a smaller home with limited or no outdoor space, consider the Ground Sun 200 (GS200) . This is a small, smart air source heat pump solution designed for apartments and small homes, as it doesn’t include an outdoor unit. It works down to –10°C, making it suitable for homes in colder climates.

Viessmann makes some of the best heat pumps on the UK market, but they are far from the cheapest. Here’s how the Viessmann Vitocal 100-A air source heat pump compares to other units in terms of price:

Properly maintaining your air source heat pump will extend its lifespan. Viessmann offers a £30-per-month, seven-year maintenance plan which can be paid via direct debit. The plan includes an annual service.

If you don’t want to pay for the maintenance plan, you can take steps to maintain your heat pump yourself. Regularly switch off the unit and remove dirt and debris that may be stuck to the fan blades, impeding the flow of air through the unit.

Keep an eye on your unit’s performance and contact Viessmann if any error codes are displayed to avoid further damage or a malfunction.

The Viessmann Vitocal 100-A air source heat pump can be combined with a hot water tank to provide both heating and hot water. (Image credit: Viessmann)

The Viessmann Vitocal is very adaptable to different houses and needs. You can buy an antifreeze kit, which uses a self-heating cable wound around the base of the external unit. It’s also a good idea for coastal homeowners to purchase the coil anti-corrosion treatment, which improves your heat pump’s ability to withstand thermal contractions and expansions and provides greater resistance to UV rays and dirt.

You can also buy a domestic hot water tank to complement your system. A recommended add-on is a horizontal outdoor buffer store which helps you further save on indoor space.

Your installer will be able to make recommendations for other add-ons that suit your home.

“This space-saving monobloc unit is suitable for most applications in new build and renovation projects and can be purchased with an output of 6kW, 8kW, 10kW, 12kW, 14kW or 16kW. It has been designed exclusively for outdoor installation and is very quiet, thanks to its advanced acoustic design (AAD). The Vitocal 100-A also has an energy efficiency rating of A+++ and uses the environmentally friendly R32 refrigerant. Furthermore, it comes complete with touchscreen control and a corrosion-resistant gold-plated heat exchanger.”

“The Vitocal 100-A heat pump is designed specifically for modernising properties, so the initial install time and costs may be substantial, yet you will benefit from a heat pump designed to operate at all times of the year. The Vitocal is an outdoor, space-saving model ideal for new build properties. It also has an energy efficiency rating of efficiency class: A+++, the highest score the rating system awards.”

“Recently had some issues with a very old ground source heat pump unit that had been playing up due to misuse. After a phone call to Viessmann, I received a very prompt response and the services of not one but two engineers. I cannot fault the hours and effort put in by the team, who really went the extra mile to get the system back up and running. I definitely felt I got value for money and would fully recommend it in future. Also, the technical knowledge and advice/recommendations received were top quality, and we were very happy.”

The Viessmann Vitocal 100-A air source heat pump is compact, highly energy-efficient, attractive and powerful. Its solid A+++ energy efficiency rating is the highest available.

That being said, the Viessmann Vitocal 100-A air source heat pump is not suitable for cold climates where temperatures drop below –5°C. If your home is in a place where temperatures drop below –5°C, the unit’s efficiency will drop. Therefore, the Viessmann Vitocal 100-A is a good complementary heat source, but there are better alternatives that work at lower temperatures.

However, the Vitocal 100-A’s adaptability and anti-corrosion properties make this range highly suitable for coastal properties and those situated in milder climates. It can be cascaded or combined with a domestic hot water tank for use in larger homes, and its compact size and monobloc design makes it a great standalone option for small properties.

We compiled our Viessmann Vitocal 100-A air source heat pump review by reading customer testimonials and opinions on sites like Google Reviews, Trustpilot and others. We also looked at professional forums, technical documentation and third-party media articles.

We then compiled a 100-point scorecard to rate the Viessmann Vitocal 100-A against, consisting of the following criteria:

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