The Ideal Heating 25 Litre Buffer Tank (AH700436, BT25) adds vital system water volume to heat pump and heating installations, helping to prevent short-cycling on systems with low water content, multiple zones, or variable heating demand. By storing a reserve of heated water, the buffer tank smooths flow temperature, supports better defrost recovery, and reduces mechanical strain on the compressor.
Built for flexible wall-hung installation in either horizontal or vertical orientation, the BT25 is compatible with Ideal Logic Air and HP290 air source heat pumps, as well as biomass and conventional gas or oil boilers. Its insulated shell limits standing heat loss, keeping the tank efficient as a passive thermal store in both domestic and light-commercial systems.
6 bar
Max Working Pressure
-10 to +110°C
Operating Temperature
Class C
Energy Efficiency
Important: Wall Loading & Expansion Vessel Sizing
The tank must be fixed to a load-bearing wall of adequate strength — this is the installer's responsibility. The system's expansion vessel must also be sized to account for the buffer tank's water content, in addition to the rest of the heating circuit.
Please Note: 25L vs 50L — Check System Sizing
This is the 25 litre (BT25, AH700436) variant. A 50 litre (BT50, AH700437) version is also available with larger physical dimensions and connections in the same sizes — confirm the required buffer volume against the heat pump manufacturer's system design guidance before ordering.
Good to Know: Compatible Heat Sources
Suitable for use with Ideal Logic Air and HP290 heat pumps, biomass boilers, and traditional gas or oil boilers — making it a versatile addition to renewable and conventional heating systems alike.
Reduces Short-Cycling
Added system volume stops the heat source switching on and off too frequently, which improves efficiency and extends compressor or burner lifespan.
Flexible Wall Mounting
Can be installed horizontally or vertically on a wall bracket, helping it fit into plant rooms, airing cupboards, or garages where floor space is limited.
Insulated Shell
The tank body is insulated to minimise standing heat loss, so stored thermal energy isn't wasted between heating demand cycles.
Supports Multi-Zone Systems
Provides a stable hydraulic buffer point for systems serving multiple heating circuits or zones with differing flow requirements.
Improves Defrost Performance
The stored water reserve helps maintain heat output to the property during an air source heat pump's defrost cycle.
Dual Connection Sizing
Fitted with both 1″ and 1¼″ connections, giving installers flexibility to match existing pipework without extra reducers.
| Product Identification |
| Manufacturer |
Ideal Heating |
| Product |
25 Litre Buffer Tank (BT25) |
| Manufacturer Part Number (MPN) |
AH700436 |
| GTIN / Barcode |
3410537004360 |
| Compatible With |
Ideal Logic Air and HP290 air source heat pumps; biomass and conventional gas/oil boilers |
| Technical Specification |
| Storage Capacity |
25 litres |
| Energy Efficiency Class |
C |
| Waste Heat Loss |
41 W |
| Maximum Working Pressure |
6 bar |
| Operating Temperature Range |
-10°C to +110°C |
| Connections |
1″ and 1″¼ |
| Mounting Orientation |
Horizontal or vertical, wall-hung |
| Colour |
Blue |
| Dimensions |
| Diameter (ØA) |
220 mm |
| Overall Height (I) |
785 mm |
| Body Height (H) |
166 mm |
| Width (E) |
450 mm |
| Depth (F) |
290 mm |
| Wall Bracket Centres (J) |
40 mm |
| Gross Weight (inc. packaging) |
12.5 kg |
What's the difference between the 25L and 50L buffer tanks?
The 25L (BT25, AH700436) and 50L (BT50, AH700437) share the same connection sizes and pressure/temperature ratings, but differ in physical dimensions, energy class figures, and heat loss — the 50L is taller and wider to accommodate the larger water volume. Sizing should be based on the heat pump manufacturer's minimum system volume requirement.
Which heat pumps is this buffer tank compatible with?
It's designed for use with the Ideal Logic Air range and the Ideal HP290, and is also suitable alongside biomass boilers and traditional gas or oil boiler systems.
Can the buffer tank be mounted horizontally?
Yes, the tank supports both horizontal and vertical wall-hung installation, giving installers flexibility depending on available plant room space.
Do I need to resize my expansion vessel when adding a buffer tank?
Yes. The additional water volume of the buffer tank must be included when calculating the system's total expansion vessel requirement, in line with the manufacturer's installation guidance.
What connection sizes does the buffer tank use?
The BT25 is fitted with 1″ and 1¼″ connections, allowing it to be plumbed into most domestic heat pump and boiler circuits without additional adaptors.
