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The authoritative engineering reference for hot water cylinder dimensions, heights, diameters, and installation clearances. Compare standard, slimline, vented, and unvented cylinder sizes to find the perfect fit for your airing cupboard or loft space.
Select a cylinder capacity to instantly see standard and slimline dimensions, minimum cupboard depth, and required installation clearances. Toggle between standard and slimline models.
Dimensions are typical for stainless steel unvented cylinders. Actual sizes may vary by manufacturer. Always verify with technical datasheet.
Detailed height, diameter, and weight data for standard unvented cylinders (90Lβ400L+). Use this chart to compare typical dimensions across all common capacities and identify the best fit for your installation space.
| Capacity | Height (Standard) | Diameter (Standard) | Height (Slimline) | Diameter (Slimline) | Empty Weight | Full Weight |
|---|---|---|---|---|---|---|
| 90 L | 900 mm | 470 mm | 1050 mm | 400 mm | 25 kg | 115 kg |
| 120 L | 1020 mm | 490 mm | 1180 mm | 420 mm | 30 kg | 150 kg |
| 150 L | 1150 mm | 510 mm | 1320 mm | 440 mm | 35 kg | 185 kg |
| 180 L | 1280 mm | 530 mm | 1450 mm | 460 mm | 40 kg | 220 kg |
| 210 L | 1450 mm | 550 mm | 1620 mm | 480 mm | 46 kg | 256 kg |
| 250 L | 1580 mm | 580 mm | 1760 mm | 500 mm | 52 kg | 302 kg |
| 300 L | 1720 mm | 610 mm | 1920 mm | 530 mm | 62 kg | 362 kg |
| 400 L | 1950 mm | 670 mm | 2180 mm | 580 mm | 78 kg | 478 kg |
Slimline models reduce diameter by approximately 50β70mm and increase height by 130β230mm to maintain equivalent storage volume. Weights are approximate and based on stainless steel construction with 50mm insulation.
When space is tight β particularly in older airing cupboards or apartments β slimline cylinders offer a narrower diameter at the expense of extra height. Below we compare the trade-offs.
| Parameter | Standard 210L | Slimline 210L |
|---|---|---|
| Height | 1450 mm | 1620 mm |
| Diameter | 550 mm | 480 mm |
| Min. Cupboard Depth | 600 mm | 530 mm |
| Top Clearance Needed | 1550 mm total | 1720 mm total |
This table helps you quickly translate your required cylinder capacity into the physical space you must allocate. Includes both unvented and vented cylinder typical dimensions.
| Capacity | Unvented (H x D) | Vented (H x D) | Recommended Cupboard (WxDxH) |
|---|---|---|---|
| 90 L | 900 x 470 mm | 850 x 450 mm | 600 x 550 x 1200 mm |
| 120 L | 1020 x 490 mm | 980 x 470 mm | 600 x 570 x 1350 mm |
| 150 L | 1150 x 510 mm | 1100 x 490 mm | 650 x 590 x 1500 mm |
| 180 L | 1280 x 530 mm | 1220 x 510 mm | 650 x 610 x 1650 mm |
| 210 L | 1450 x 550 mm | 1400 x 530 mm | 700 x 630 x 1800 mm |
| 250 L | 1580 x 580 mm | 1520 x 560 mm | 700 x 660 x 1950 mm |
| 300 L | 1720 x 610 mm | 1680 x 590 mm | 750 x 690 x 2100 mm |
While the external dimensions of direct and indirect cylinders of the same capacity are often identical, there are internal differences that affect installation. Direct cylinders house immersion heaters only; indirect cylinders include a heating coil that adds marginally to height in some designs.
Typically same height/diameter as standard models. May have additional bosses for two immersion heaters (primary & boost). No coil penetration, so slightly lighter.
Coil connections (flow & return) protrude from the side, adding 30β50mm to the effective diameter for clearance. Ensure cupboard width accounts for pipework.
Vented cylinders are generally slightly smaller for the same storage capacity because they rely on a header tank for pressure; unvented cylinders must accommodate a thicker wall and safety components.
| Feature | Vented Cylinder | Unvented Cylinder |
|---|---|---|
| Wall Thickness | 0.8β1.2 mm | 1.2β2.0 mm (stainless steel) |
| Height (same capacity) | Slightly shorter (5β10%) | Standard |
| Weight | Lighter (copper or thin steel) | Heavier (stainless steel) |
| Additional Components | None on cylinder | Expansion vessel, PRV, tundish externally |
Heat pump cylinders require a larger internal coil (3.0β4.5 mΒ² surface area) which often increases the cylinder diameter or height slightly. For the same nominal capacity, expect a 5β10% larger footprint compared to a standard indirect cylinder.
For a 210L heat pump cylinder, height is typically 1500β1600mm and diameter 560β580mm. Always specify a cylinder with a dedicated heat pump coil and ensure cupboard depth accommodates the additional coil connections.
Accurate measurement of your available space is critical. Below are the minimum recommended internal dimensions for cupboards housing unvented cylinders.
| Cylinder Size | Min. Cupboard Width | Min. Cupboard Depth | Min. Cupboard Height |
|---|---|---|---|
| 90 L | 550 mm | 550 mm | 1200 mm |
| 120 L | 570 mm | 570 mm | 1350 mm |
| 150 L | 590 mm | 590 mm | 1500 mm |
| 180 L | 610 mm | 610 mm | 1650 mm |
| 210 L | 630 mm | 630 mm | 1800 mm |
| 250 L | 660 mm | 660 mm | 1950 mm |
| 300 L | 690 mm | 690 mm | 2100 mm |
Add 100mm to height for top clearance and 50mm each side for installation access. Loft installations require a structural platform and frost protection.
Building Regulations Part G3 mandates adequate clearance for safety devices, maintenance, and discharge pipework routing. The following clearances must be maintained:
Minimum 100 mm above the cylinder for expansion vessel access and tundish visibility.
At least 50 mm around the cylinder body, increasing to 150 mm where valves/connections are located.
Ensure 600 mm of clear working space in front of the cylinder for servicing immersion heaters and controls.
Floor loading is an important consideration, especially for loft installations or suspended timber floors. A full 210L cylinder weighs over 250 kg.
| Capacity | Empty Weight | Full Weight | Floor Loading (on 0.6mΒ²) |
|---|---|---|---|
| 90 L | 25 kg | 115 kg | 1.9 kN/mΒ² |
| 120 L | 30 kg | 150 kg | 2.5 kN/mΒ² |
| 150 L | 35 kg | 185 kg | 3.1 kN/mΒ² |
| 180 L | 40 kg | 220 kg | 3.7 kN/mΒ² |
| 210 L | 46 kg | 256 kg | 4.3 kN/mΒ² |
| 250 L | 52 kg | 302 kg | 5.0 kN/mΒ² |
| 300 L | 62 kg | 362 kg | 6.0 kN/mΒ² |
Most domestic floors are designed for 1.5β2.0 kN/mΒ² imposed load. Always check structural capacity before installation.
Higher insulation thickness improves ERP rating but adds to the overall cylinder diameter. Modern cylinders use 50β75mm of polyurethane foam; some slimline models sacrifice insulation thickness (down to 40mm) to reduce diameter, slightly increasing standing heat loss.
An A-rated 210L cylinder typically has 60mm insulation and a diameter of 560mm. A C-rated slimline model may have 45mm insulation and a diameter of 500mm but 15% higher standing heat loss.
V = Ο Γ rΒ² Γ h
Q = m Γ c Γ ΞT
Heat Loss = U Γ A Γ ΞT
Scenario: Available cupboard depth 520 mm, width 600 mm, height 1900 mm. Need 150L capacity.
Solution: Choose a 150L slimline cylinder (440mm diameter, 1320mm height). Cupboard depth 520 mm > 440mm + 50mm clearance = 490 mm required. Total height 1320mm + 100mm top clearance = 1420mm < 1900mm. β Perfect fit.
Existing: Vented 117L (36"x18") cylinder in cupboard 700x600x1800mm. Wants upgrade to 210L unvented.
Check: Standard 210L unvented: 550mm diameter, 1450mm height. Cupboard depth 600mm > 550+50=600mm (tight but acceptable). Height 1450+100=1550mm < 1800mm. Recommend slimline 210L (480mm dia, 1620mm height) for comfortable clearance.
Requirement: 250L heat pump cylinder with large coil. Typical dimensions: 580mm diameter, 1680mm height. Ensure cupboard depth β₯ 630mm and height β₯ 1780mm. Weight full ~310 kg β check floor loading.
Always measure your available space accurately, accounting for pipe runs, valves, and safety devices. Remember that copper cylinder dimensions may differ slightly from stainless steel.
Before ordering, download the technical datasheet for the exact model. Pay attention to overall height, diameter including insulation, and weight.
Choosing a cylinder that fits your available space is just as important as selecting the right capacity. Use our dimensions chart and interactive calculator to find a model that satisfies both your hot water demand and your cupboard constraints. When in doubt, consult a G3-certified plumbing engineer.
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