Frequently asked questions

An unvented hot water system has no cold water feed tank but rather has a sealed (unvented) hot water cylinder fed directly from the cold water mains and uses mains pressure. The unvented cylinder maintains a steady pressure from an incoming water supply. Unvented systems are ‘sealed/closed’ systems and so require additional ancillary equipment, such as an expansion vessel to manage the changes in pressure within the system as the water within heats up, and a pressure reducing valve to regulate the pressure of the incoming cold water.

• R744 Carbon Dioxide CO2: Natural refrigerant with ultra-low GWP of 1, very eco-friendly and non-flammable.

• R290 Propane: Natural refrigerant with ultra-low GWP of 3, very eco-friendly and highly flammable.

• R32 HFC-32: Low GWP of 675, eco-friendly, mildly flammable, lower cost, most popular refrigerant choice.

• R410A Puron, AZ-20: Slowly being phased out, high GWP of 2088, worse for the environment, non-flammable, higher costs.

• R407c Klea66: Still used but will be phased out in 2025 in systems with less than 3kg charge, high GWP of 1774.

Expansion vessels contain air or an inert gas such as nitrogen – as well as water from the system - separated by a membrane that is either a rubber bag or bladder, or a rubber sheet or diaphragm. Water in the expansion vessel expands as the cold, pressurised mains water is heated. As it does, the air within the vessel is compressed to absorb the increased volume, managing the impact of the pressure increase. As the water cools, its volume decreases, and the water level drops again.

Unvented systems save space because they don’t need a separate cold water tank and the associated pipework that links it across the system. They therefore have a greater capacity for large commercial or residential properties to deliver hot water across complex designs and longer pipe runs. They also usually have stronger water pressure than tank fed systems as the pressure comes from the mains feed, and water outlets like taps and showers give a better performance. There is far less risk of unvented systems freezing in winter and they are less likely to become contaminated – something that can happen with vented systems due to the use of an open tank.

A hybrid heating system combines two or more heat sources in a hydraulic water-based heating system to satisfy the total load. Typically, this type of system combines a heat pump with a gas or direct electric boiler and alternates between the two, depending on which one is the most efficient. The benefits of a hybrid system include improved energy efficiency, lower heating costs, and greater flexibility. Read more about the benefits of a hybrid heating system in our latest case study HERE.

Flow through vessels have been specifically developed to reduce the risk of stagnation and contamination from slow moving water. They do this by keeping water moving through the expansion vessel using a Flowjet valve. Hamworthy Heating can provide standalone flow through expansion vessels and a Flowjet valve that diverts part of the water flow in the system into the vessel, preventing water stagnation and guarding against the breeding of harmful bacteria – most notably legionella (which causes the potentially fatal Legionnaires disease).The Flowjet valve also allows for expansion vessels to be drained, bypassed or isolated during removal or replacement. The flow through expansion vessel from Hamworthy Heating also has an internal bladder manufactured in Butyl rubber to limit the risk of bacteria growth, which makes it particularly suited to healthcare premises.

Yes, Tyneham heat pumps have a wide range of commercial and industrial applications, including new build, refurbishment and retro fit. Any commercial building can benefit from a heat pump as long as it has effective insulation, external space for the heat pump unit, and the unit is correctly sized, as well as having access to a sufficient electrical supply.

A flow through expansion vessel reduces the risk of legionella growth in an unvented system as the design of the vessel and valve keep water moving, reduces the amount of pipework in the system and gives more flexibility for maintenance and replacement.

When a hot water system is running as usual, the expansion vessel will regularly partially empty and then refill, exchanging water with the system. However, expansion vessels are known to be points that run the risk of bacterial growth as they can suffer from low flow rates or stagnant water. This is particularly true if the system is unused, or the pressure and temperature remain steady over a period of time. In that case the normal fill and replace cycle won’t be naturally changing the water and bacteria can flourish.

A heat pump is an appliance that extracts heat energy from the environment, ground, water or air and upgrades it to useful heat for central heating and domestic hot water.

Yes, in hard water areas, limescale occurs when water is heated and excess minerals in the water accumulate and become drawn to the hottest point, which is often the tank surface and the heat exchanger. Carbon dioxide and calcium within water combine to form calcium hydrogen carbonate. When heat is applied to water, the composition breaks down and the insoluble calcium carbonate (CaCO₃) forms scale deposits on heat exchangers and tank surfaces.

With the scale acting as an insulator, more heat is required to permeate the scale and heat the water. As a result, heat-up times lengthen, recovery times increase, and more energy is used for the same output. With approximately every 1mm of scale reducing efficiency by 7–10%, this is an important consideration in terms of running costs. Moreover, as the metal underneath the scale eventually starts to corrode due to the increasingly acidic conditions, a breakdown could occur. For more information on water heater maintenance, sign up for our CIBSE approved CPD on ‘Best Practise in Domestic Hot Water’ HERE.

There are several types of commercial heat pump the most common ones being: air source, commonly called air to water, ground source and water source. All Hamworthy Heating commercial heat pumps are monobloc air source heat pumps. For more information on the Tyneham range visit HERE.

Limescale comes from the remnants of dissolved minerals such as calcium carbonate, magnesium or gypsum present in our water supply. When it rains, the water filters through limestone and chalk and collects in an underground layer called an aquifer. Despite the extensive filtration process performed by water suppliers, these dissolved minerals can still end up in water and depending on geographical location, can affect the performance of boilers, heaters and water heaters. For more information on water composition visit HERE.