Steam generator water filtration: Harvia HWF filters explained

The short answer

• Harvia’s HWF is a cartridge water filter for its steam generators and combi heaters. It comes in two sizes: M (HWF01M) for home use and XL (HWF01XL) for commercial use. The replacement cartridges are HWF-F-M and HWF-F-XL.
• It reduces hardness by ion exchange. Harvia calls it a water filter, but its manual says the cartridges “soften cold tap water”, reducing lime and carbonate hardness. Carbon and particle stages also take out particles, smells and tastes such as chlorine.
• Capacity is measured in litres, and it depends on the water. The harder the water, the fewer litres a cartridge treats. A water meter on the outlet shows how much is left.
• Change the cartridge when its capacity is used up, or after 12 months at the latest, as Harvia recommends.
• It is plumbing. The filter goes on the cold supply to the generator, with a stop valve, and Harvia says only qualified people may install and maintain it. In Australia that means a licensed plumber.
• Not every steam generator needs one. Test the water at the site and compare it with the generator’s manual. Our water quality guide covers hardness across South East Queensland.

Each point below is labelled with its source: Harvia for something Harvia publishes for a named product, and general good practice for advice supported by several sources. We have not set a BSC interval or product for water treatment, so none is given here.

Why water treatment matters

A steam generator boils water and sends out pure steam. The minerals that were dissolved in the water stay behind in the tank. Over time they form scale on the elements, the water-level sensor and the drain. That cuts steam output, causes level faults and shortens the generator’s life. Our water quality guide explains how scale forms and how the generator’s own draining and flushing help.

Treating the water before it reaches the generator means fewer minerals go into the tank in the first place. Harvia’s product page recommends filtration for its steam generators and combi heaters, because unfiltered hard water calcifies the tank and other parts and shortens the equipment’s life.

Filtration, softening and purification are not the same thing

These words get used loosely, and they describe different processes. The differences explain why one product can’t be swapped for another without checking.

Harvia: the HWF combines the first two. Its cartridge has a particle and carbon pre-filter, ion exchangers that remove lime, and a final carbon and particle stage. Harvia’s HWF manual rates its chlorine reduction to EN 14898 class 1.

Harvia: reverse-osmosis or demineralised water is not discussed in the HWF manual or in the HGX manual we reviewed. One other manufacturer limits how pure the water for its commercial generators can be, because its level sensors need some dissolved minerals to work. So the question goes to Harvia, or to the maker of whichever generator is selected, before the water is purified.

What the Harvia HWF is

Source: Harvia HWF01M/HWF01XL Instructions for Installation and Use (05082020/Y05-0810) and Harvia’s product pages. The kit includes the filter head, cartridge, wall bracket, hoses, adapters, a water hardness tester and a water meter. A replacement meter with a digital display is sold as a spare part (HWF-M-LCD).

Harvia’s product pages describe the HWF for steam generators and combi heaters in home or commercial use. Each product page lists the generator models it works with; check that the selected model is on the list for the size chosen. An older small version, HWF01S, is now listed by Harvia as discontinued.

How it works, in Harvia’s words

Harvia’s manual describes water flowing through four stages:

1. Pre-filtering: a particle filter and activated carbon, which takes out unpleasant smells and tastes such as chlorine.
2. Ion exchangers that remove lime.
3. Activated carbon again.
4. Particle filtration at the outlet.

The bypass setting. The filter head has four settings, 0 to 3. The bypass sends a set share of the water past the ion exchangers, through only the carbon and particle stages. It is then mixed back with the ion-exchanged water at the outlet. A higher bypass setting means more litres per cartridge but less hardness removed. Harvia’s manual gives “2” as the factory default and quotes its capacities at that setting. Its quick-start page for steam generators recommends setting 0 to filter out the most impurities. Why this matters: the bypass setting and the water’s hardness together decide how long a cartridge lasts, so they need to be set and recorded at installation.

Harvia: ion-exchanged water is slightly acidic, because it contains carbonic acid. Harvia recommends against copper components, or components coated with zinc, chrome or nickel, between the filter and the generator, to avoid corrosion. Your plumber should take this into account when choosing fittings for that section.

Capacity and when to change the cartridge

Harvia: a cartridge treats a set number of litres, and that number falls as the water gets harder. Harvia’s manual has a table of capacities for each size and bypass setting across a range of carbonate hardness. Its headline figure is an average of 3,800 L for the M and 6,800 L for the XL. That figure assumes 10 °dH, bypass setting 2 and the standard 1.5 m hoses. Harvia notes that actual capacity can be higher or lower, depending on the water quality, flow rate, pressure and how steady the flow is.

Harvia’s replacement criteria:

• Capacity: the cartridge must be replaced when it reaches the capacity in Harvia’s table for the water’s hardness and the bypass setting.
• Time: Harvia recommends replacing it every 12 months even if capacity is left. The manual asks for the installation date and the replacement date, no more than 12 months later, to be written on the cartridge label.
• Water changes: at each cartridge change, Harvia asks for the incoming carbonate hardness to be checked again, and the interval and bypass setting updated if it has changed.

Whichever comes first applies. A home steam room used a few times a week may reach the 12-month limit first. A busy commercial room can use up an XL cartridge much sooner. That is why there is no single replacement interval for everyone.

Monitoring. The water meter fits on the outlet side of the filter. Once it is programmed as its instructions describe, it shows how much capacity is left at any time. Harvia’s troubleshooting table lists three reasons a generator scales up too fast with the filter fitted: the wrong bypass setting, the capacity being exceeded, or a filter that is too small for the job.

Carbonate hardness is not total hardness

Harvia sizes the HWF by carbonate hardness (°dKH), and the kit includes a quick test that reads in those units. Seqwater’s reports, which our water quality guide summarises, give total hardness in mg/L as calcium carbonate. These are related but not the same measurement, so a zone average can’t simply be read off Harvia’s table. General good practice: test the water at the property in the units the filter manual uses, or ask your water supplier for carbonate hardness, as Harvia suggests.

Installation

The HWF goes on the cold water supply to the generator. Harvia’s manual sets out the essentials:

Harvia: the filter also publishes its own pressure loss, about 0.40–0.50 bar at 180 L/h depending on size. The generator still has its own flow and pressure requirements. Harvia’s HGX manual, for example, asks for a maximum of 4.0 bar and a supply flow of 8–12 L/min. General good practice: the plumber checks that, with the filter fitted, the generator still gets the flow and pressure its own manual requires.

Plan access for the filter

A filter that is hard to reach doesn’t get changed, and an exhausted cartridge gives no protection. Plan its place at the same time as the generator’s. Our steam generator location and service access guide covers the plant space as a whole. For the filter specifically:

• Close to the generator’s water inlet, on a wall that takes a solid fixing.
• Clearance to change the cartridge. Harvia asks for at least 65 mm between the cartridge and the floor or opposite wall, plus room for hands and the cartridge to come out.
• A readable meter and a reachable stop valve.
• Somewhere to rinse to. Each new cartridge is rinsed with several litres to a drain or a container, so a floor drain or space for a bucket helps.
• Within the temperature limits. Harvia’s manual gives 4–30 °C for the surroundings. It also asks for protection from frost, direct and indirect sunlight, heat sources, and chemicals or fumes. That last point rules out pool chemical stores. In Queensland, a hot roof space or unventilated cupboard can exceed 30 °C, which is also a problem for the generator.

Looking after the filter

Harvia’s maintenance list:

• check the system for leaks: daily;
• check the pressure hoses for cracks: regularly;
• replace the cartridge: at capacity or after 12 months;
• rinse the filter with 4–5 litres after a break of more than two days, and rinse it as at first installation after more than four weeks;
• close the inlet stop valve if the steam room won’t be used for a long time;
• replace the pressure hose after 5 years and the filter head after 5–10 years;
• clean the outside with a damp cloth only, with no corrosive chemicals, and handle the cartridge hygienically when changing it.

Harvia: if the water supplier issues a boil-water notice, it applies to filtered water too. Once the notice is lifted, Harvia’s manual says to replace the cartridge and clean the system, including connectors and hoses.

A filter doesn’t replace generator maintenance. The HWF manual does not say the filter replaces descaling or servicing. Harvia’s generator manuals still set out descaling, emptying the sediment cup, cleaning the water-level sensor and, for community and institutional use, a thorough service at least twice a year. Our steam generator maintenance guide explains those tasks and who does them.

Does every steam generator need filtration?

No single answer covers every steam room. Whether treatment is needed, and what kind, depends on four things:

• The water at the property. Hardness varies from one supply zone to the next and from month to month. Across South East Queensland, Seqwater’s averages range from soft on the Gold Coast to moderately hard in Brisbane and the Scenic Rim. See the figures in our water quality guide.
• How much the generator runs. More hours of boiling means more water, more minerals and faster scale. A commercial generator can use in weeks what a home generator uses in a year.
• The manufacturer’s limits. Harvia: its HGX manual recommends a softener on the building’s supply where the tap water is hard. It also makes its guarantee depend on the water table in the manual. Other manufacturers set their own thresholds, and some require softening for all commercial or public use.
• Other water quality. Hardness is not the only concern. Harvia’s water table also covers iron, manganese, chloride and more, so a full water test is more useful than a hardness strip.

General good practice: test the incoming water at the site before the generator is chosen. Then compare the result with the selected generator’s manual and choose the treatment, if any, from there. In soft water a home steam room may need only the generator’s own flushing and regular descaling. In harder water, or in commercial use, treatment is usually part of the plan. For high-volume commercial rooms, a cartridge filter may not be the most practical option; Harvia also offers a salt-regenerated softener for commercial use. Check its availability for Australia with Harvia’s local supplier.