GWS HeatWave Hydronic Expansion Tanks
GWS HeatWave HWB-INT-300LV Heating expansion tank
- Established 1975
- Trusted by thousands of customers
The GWS HeatWave™ HWB-INT-300LV is a 300 litre vertical expansion vessel for closed-loop heating and chilled water systems. As the system water heats and expands, the vessel’s air-charged chamber takes up the extra volume, holding system pressure steady and keeping it off the relief valve.
Unlike the smaller HeatWave tanks, the INT models have an exchangeable butyl membrane, so the bladder can be replaced in situ if it ever fails, and are rated to 10 bar rather than 6. Steel shell on three legs with a 1¼″ BSPT connection, factory pre-charged to 1.5 bar, up to 99 °C.
Closed-loop heating
10 bar rated
1¼″ BSPT
Freestanding on legs
Model HWB-INT-300LV
More about this product
Product overview
The GWS HeatWave™ HWB-INT-300LV is a 300 litre (79.2 US gal) vertical expansion vessel for sealed, closed-loop heating and chilled water systems. Water expands as it heats. Without somewhere to go, that extra volume pushes system pressure up until the relief valve lifts. The HeatWave’s air-charged chamber absorbs it instead, keeping pressure steady through every heat-up and cool-down.
The INT models are the large-system end of the HeatWave range. They differ from the smaller tanks in two ways: the butyl membrane is exchangeable, so it can be replaced through the top of the vessel rather than scrapping the whole tank, and the shell is rated to 10 bar instead of 6, which matters on taller buildings and higher-pressure plant. The vessel stands on three welded legs with a 1¼″ BSPT connection at the base.
Key features
Typical applications
Technical specifications
| Brand / Series | GWS — HeatWave™ INT |
| Model | HWB-INT-300LV |
| Type | Vertical, freestanding on legs, exchangeable membrane |
| Nominal volume | 300 L / 79.2 US gal |
| Connection | 1¼″ BSPT |
| Factory pre-charge | 1.5 bar / 22 psi |
| Max operating pressure | 10 bar / 150 psi |
| Operating temperature | −10 °C (avoid freezing) to +99 °C |
| Membrane | High-grade butyl, exchangeable |
| Air valve | Brass, O-ring sealed cap |
| Finish | Dual-layer polyurethane over epoxy primer |
| Height (A) | 1,238 mm |
| Diameter (B) | 680 mm |
| Gross weight | 44.5 kg |
| Suitable for | Closed-loop, non-potable heating and chilled water only |
Frequently asked questions
What does “exchangeable membrane” mean?
The butyl membrane inside the vessel is held by a flange rather than welded in, so if it fails after years of service it can be replaced on site. Smaller HeatWave tanks have a fixed diaphragm and are replaced as a whole.
Can I use it on a drinking-water or booster system?
No. HeatWave™ vessels are for closed-loop, non-potable heating and cooling only. For drinking water or pump boosting, use a GWS PressureWave™ or Challenger™ vessel.
What should the pre-charge be set to?
It arrives at 1.5 bar. Check it with the vessel empty and set it to your system’s cold fill pressure before filling.
Can I use antifreeze?
Yes, propylene glycol at concentrations up to 50%. GWS advise avoiding ethylene glycol.
Is 300 litres the right size?
Vessel size depends on system water volume, cold fill pressure and maximum temperature. The INT range also comes in 200 and 500 litres. Ask our team if you’d like it sized for your system.
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Data Sheet PDFDownload
Standard delivery:
Standard delivery is free on most orders. Some items may incur a delivery charge depending on weight, size or value. Any applicable charge will be displayed at checkout.
Deliveries will typically be made between 7am and 6pm, Monday to Friday (excluding public holidays).
Next day delivery:
Next working day delivery is available for a £16.50 + VAT delivery charge.
Orders must be placed before 12 noon to qualify for next working day delivery. Orders placed after 12 noon on Thursday but before noon on Friday will be delivered the following Monday. Orders placed after 12 noon on Friday will be delivered on Tuesday.
Pallet/Large/Difficult items:
Some large, heavy or difficult to transport items may incur an additional delivery charge. Please contact us for a delivery quote before ordering.
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Frequently Asked Questions
Quick answers to common questions about the GWS HeatWave HWB-INT-300LV Heating expansion tank. For technical specifications, see the product details above; for sizing or installation advice, contact our team. If you have any other questions, we're happy to help.
What is an accumulator tank?
An accumulator tank is a pressurised vessel that connects directly to the mains supply and stores water under pressure. When a tap or shower opens, water discharges immediately from the vessel at full mains pressure rather than drawing only from the street main. This delivers stronger, more consistent flow at peak times. Accumulators have no pump and no moving parts so they are maintenance free and silent.
When should I use an accumulator instead of a pump?
An accumulator is the right solution when static mains pressure is adequate – above 2 bar – but flow is poor or drops during peak demand. It boosts available flow without adding a pump, energy use or noise. If static pressure is below 2 bar, a booster pump is needed instead, or an accumulator combined with a charge pump such as the WaterBoost ACF1.
What size accumulator do I need?
Accumulators are typically sized on a 60 per cent usable rule – a 300 litre vessel delivers around 180 litres of boosted water per cycle. As a guide, a 2 to 3 bedroom home suits a 300 litre vessel such as the GWS GCB-300LV. Larger 4 to 5 bedroom homes or properties with multiple bathrooms typically need 450 to 600 litres. Vertical models save floor space, horizontal models suit lofts and roof spaces.