WaterBoost Accumulator Vessels
WaterBoost 450 Litre Horizontal Accumulator Vessel AWBH-450LH
- Established 1975
- Trusted by thousands of customers
The WaterBoost AWBH-450LH is a 450-litre WRAS-approved horizontal accumulator vessel for mains-connected water systems — the largest in the horizontal range. The horizontal orientation makes it ideal where headroom is limited, fitting on its side in a loft, cupboard or plant room. Accumulators store mains water under pressure so you draw instantly at full mains pressure the moment you open a tap or shower, delivering noticeably stronger, more consistent flow even during peak demand periods.
The AWBH-450LH operates on a 60% usable volume ratio — delivering approximately 270 litres of high-pressure water before returning to normal mains flow. At a typical shower flow of 12 l/min, 270L supports two simultaneous showers for approximately 11 minutes, or three showers for approximately 7.5 minutes. Diaphragm design, WRAS-approved construction, maintenance free. Suited to 3 bedroom+ and larger properties with higher simultaneous demand where a vertical vessel won’t fit.
Requires a minimum 2 bar static mains pressure to operate effectively. If your static pressure is below 2 bar, add the WaterBoost ACF1 accumulator booster pump to charge the vessel to the required working pressure.
Horizontal — low headroom
Largest horizontal model
Maintenance free
No pump — no power
3 bedroom+ homes
ACF1 pump if <2 bar
More about this product
Product overview
The WaterBoost AWBH-450LH is a 450-litre WRAS-approved horizontal accumulator vessel for mains-connected cold water systems, and the largest horizontal model in the WaterBoost range. It installs on its side on saddle feet — ideal for lofts, low-ceiling cupboards and plant rooms where a vertical 450-litre vessel would not stand upright. It stores mains water under pressure so that when you open a tap or shower, water discharges immediately at full mains pressure rather than waiting for the street main to respond.
The vessel operates on a 60% usable volume ratio, delivering 270 litres of high-pressure water per charge before recharging automatically from the mains. Diaphragm design, WRAS-approved construction, maintenance free and completely silent — no pump, no electronics, no servicing required once installed.
Requires a minimum 2 bar static mains pressure. If your pressure is below 2 bar, add the WaterBoost ACF1 boost pump to charge the vessel to the required working pressure.
WRAS approved · Maintenance free · Silent operation
Why choose horizontal?
How it works
| 1 — Vessel fills under mains pressure | The accumulator connects to the mains and fills automatically. The internal diaphragm compresses as water enters, storing energy as pressure. |
| 2 — Water discharges at full pressure | When a tap or shower opens, pressurised water discharges immediately from the vessel — strong, consistent flow from the first moment. |
| 3 — Vessel refills from mains | Once demand ceases, the mains refills the vessel automatically. No pumps, no controls, no maintenance — entirely self-managing. |
Key features
Sizing guide
Recommended vessel sizes for the AWBH horizontal range, based on property type.
| Property | Recommended vessel | Usable output |
|---|---|---|
| 1–2 bedroom home | 150L | 90L |
| 2–3 bedroom home | 200L or 250L | 120L or 150L |
| 3+ bedroom home | 300L | 180L |
| 4–5 bedroom or multiple bathrooms — this product | 450L | 270L |
To calculate your own usage: multiply vessel size × 0.6 to get usable litres, then divide by your total flow demand to find duration. The AWBH-450LH delivers 270L usable — with two showers at 12 l/min each, that is approximately 11 minutes of simultaneous boosted flow.
Technical specifications
| Brand / Model | WaterBoost — AWBH-450LH |
| Vessel capacity | 450 litres |
| Usable output (60% rule) | 270 litres per charge |
| Orientation | Horizontal |
| Vessel dimensions | 1,822 mm long × 662 mm diameter, plus feet |
| Feet | Saddle feet, supplied |
| Max working pressure | 10 bar |
| Internal design | Diaphragm |
| WRAS approved | Yes — potable water |
| Maintenance | Maintenance free |
| Min mains pressure required | 2 bar static (resting) |
Frequently asked questions
How much does it cost?
£XXX.00 + VAT (£XXX.00 inc VAT). Please contact us for delivery timescales on this product.
Does the horizontal orientation affect performance?
No. Accumulator vessels perform identically whether oriented vertically or horizontally. The horizontal AWBH range delivers the same pressure, flow and usable volume as an equivalent vertical AWB vessel of the same capacity.
Can it go in the loft?
Yes — that is what the horizontal range is for. Check the 662 mm diameter against the hatch, and have the joist loading confirmed for 450 kg of water plus the vessel before installing.
What mains pressure do I need?
A minimum 2 bar static (resting) mains pressure is required. If your static pressure is below 2 bar, add the WaterBoost ACF1 accumulator booster pump to charge the vessel to a higher working pressure.
Should I choose this size or a smaller vessel?
The AWBH-450LH is the largest in the horizontal range, suited to 4–5 bedroom homes and properties with multiple bathrooms in simultaneous use. For a 3-bedroom home the AWBH-300LH is usually sufficient; for a 2–3 bedroom home see the 200 and 250 litre horizontals.
Does the accumulator need any ongoing maintenance?
No. WaterBoost accumulators are maintenance free. The pre-charge pressure can be verified periodically using a standard tyre pressure gauge on the Schrader valve and topped up if necessary — no specialist knowledge required.
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data sheet PDFDownload
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Manual 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 WaterBoost 450 Litre Horizontal Accumulator Vessel AWBH-450LH. 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.