Metropolitan Natural Trench Heaters are LTHW natural trench heaters from SPC, recessed into the floor beneath full height glazing to counter cold down-draughts with no fans. Cool air falling from the glass drops into the trench, passes through the heat exchanger and rises back up the window as warm air.
Manufactured in Leicester by S & P Coil Products Limited and independently tested to BS EN 16430, Metropolitan Natural Trench Heaters suit commercial, public and residential buildings with large glazed areas, including offices, hotels, restaurants and libraries. They fit screeded or suspended floors, in three widths, three heights and 24 standard lengths, with bespoke sizes on request.
Natural convection
No fans: warm air rises from the trench on its own
Any floor
For screeded or suspended floors, from 90 mm deep
BS EN 16430
Performance independently tested to BS EN 16430
Made in Leicester
Manufactured and supported by SPC in the UK
120 to 2,388 W
Heat output per unit at 80/60°C water and 20°C room air, from 150 x 90 mm at 900 mm long to 300 x 200 mm at 3,100 mm long
90 to 200 mm
Three unit heights (90, 145 and 200 mm) and three widths (150, 225 and 300 mm) to suit the floor build-up
24 lengths
From 800 to 3,100 mm in 100 mm steps, joined with flangeless end plates for continuous runs
15 finishes
Anodised aluminium roll-up grilles in satin silver, black and Anolok colours, with stainless steel on request
What are Metropolitan Natural Trench Heaters?
A Metropolitan Natural Trench Heater is a black powder coated steel casing set into the floor, holding a heat exchanger of copper tubes expanded into aluminium fins, with a roll-up grille that sits level with the finished floor. There are no fans: hot water through the heat exchanger warms the air around it and natural convection does the rest.
The unit is installed close to the glazing with the heat exchanger on the window side. Cool air falling from the glass drops into the trench, picks up heat and rises back over the window, then circulates around the room before it cools and falls to the floor.
Metropolitan Natural Trench Heaters beneath full height glazing at 244-254 Cambridge Heath Road, London
What sizes do Metropolitan Natural Trench Heaters come in?
Metropolitan Natural Trench Heaters come in three widths and three heights, in 24 standard lengths from 800 to 3,100 mm in 100 mm steps. Longer runs are made by joining units end to end with flangeless end plates.
| Width (mm) | Heights (mm) | Width at feet (mm) | 2-port valve and actuator |
|---|---|---|---|
| 150 | 90, 145 or 200 | 200 | Fitted outside the trench on 90 and 145 mm heights; outside or inside on 200 mm |
| 225 | 90, 145 or 200 | 275 | Outside or inside the trench |
| 300 | 90, 145 or 200 | 350 | Outside or inside the trench |
Bespoke widths, heights and lengths, curved sections and grilles, and corner kits with angled sections and mitred corner grilles are available on request.
Planning trench heating for a glazed building? Read our guides: Why Trench Heating is Ideal for Modern Buildings and How Do You Stop Cold Down-Draughts from Full Height Glazing? You can also see the full SPC trench heating and cooling range.
How do Metropolitan Natural Trench Heaters perform?
Output depends on the width, height and length of each unit, so a run of Metropolitan Natural Trench Heaters can be sized to the heat loss along the glazing.
- Outputs published at 80/60°C water and 20°C room air (ΔT 50°C)
- Up to 2,388 W from a 300 x 200 mm unit, 3,100 mm long
- Heat exchanger pressure tested to 22 barg, air under water, before fitting
- 15 mm plain copper flow and return connections, front or side entry, with a vent plug to purge air
Where can natural trench heaters be installed?
Metropolitan Natural Trench Heaters suit indoor spaces with large glazed areas, as single units or continuous runs.
- Screeded (concrete) or suspended floors, with levelling screws at each corner and adjustable support feet
- Continuous runs can include angle, corner and dummy sections under one continuous grille
- Grilles suit occasional foot traffic, not point loads such as chair legs
- Not for doorways or areas of constant footfall, or outdoors
Full heat output and water pressure drop data for every width, height and length is in the Metropolitan Trench Heating and Cooling brochure.
Metropolitan Natural Trench Heater grilles, controls and options
Metropolitan Natural Trench Heaters are supplied as standard with an anodised aluminium roll-up grille and a matching trim for the edge of the casing. The double-T profile blades give a free area of 60%.
Grilles and trim come in satin silver, black and a range of Anolok bronze, gold, umber and blue-grey finishes. Stainless steel grilles are available on request (grille trim is not available in stainless steel). Roll-up grilles suit occasional foot traffic, but not point loads such as chair legs.
Metropolitan Natural Trench Heaters have no fans, so they are controlled on the water side. SPC supplies 2-port control valves and actuators, and a range of wall mounted room thermostats.
- On/off control: the valve opens and closes the hot water supply as the room temperature falls and rises
- Single unit: the valve can be fitted inside the casing where it fits, with a junction box
- Zone or run of units: one valve in the main flow or return pipework controls every unit in the zone
- Valve sizes: the 2-port valve and actuator are fitted outside the trench on the 150 x 90 and 150 x 145 mm sizes
- Connections: flexible hoses with integral quarter turn isolating valves are available
- TRVs: thermostatic radiator valves are not recommended, as a head inside the trench cannot sense the room temperature
Metropolitan Natural Trench Heaters can be adapted to the building, with bespoke widths, heights and lengths, curved sections and grilles, and corner kits with angled sections and mitred corner grilles. Contact SPC to discuss project-specific requirements.
Each unit arrives fully assembled, with transverse bracing and a protective cover to keep in place while the floor is finished. The grille and trim are packed separately and fitted once the unit is installed. In a screeded floor, pipework and any conduit for valve wiring are brought into the casing before the screed is laid.
Project support from SPC: from survey to commissioning
SPC manufactures and supplies Metropolitan Natural Trench Heaters for installation by your chosen mechanical and electrical contractor, and supports the project at every stage. Our Trench CPD is CIBSE approved and can be booked for your practice.
Site surveys
SPC can visit site to review trench positions, dimensions and layout before order.
Selection and layout
Send us your drawings and design conditions and SPC will select unit widths, heights and lengths.
Trench CPD
Our CIBSE approved CPD, Design Considerations for Trench Heating, can be delivered to your practice.
Area Sales Managers
Your local SPC Area Sales Manager is on hand for questions, site visits and installation queries.
- Ready for site: each unit is labelled with its serial number, model reference and site reference, and arrives with a protective cover to keep in place until the grilles are fitted.
- Installation, operation and maintenance: IOM 76, the Metropolitan Natural Trench Heaters manual covering installation, commissioning, maintenance and fault finding, is supplied with every unit.
Specifying Metropolitan Natural Trench Heaters
Unit selection from SPC and a free BIM object for your model.
Get a unit selection
Send us your drawings and design conditions and SPC will select Metropolitan Natural Trench Heater widths, heights and lengths for your project.
Download BIM objects
Add Metropolitan Natural Trench Heaters to your BIM model. The BIM object is free to download from SPC on bimstore, alongside the rest of the SPC range.
SPC trench heating in UK projects
SPC trench heating has been installed beneath full height glazing in buildings across the UK, including offices, schools, libraries, museums, hotels and visitor centres. Metropolitan Natural Trench Heaters were chosen for 244-254 Cambridge Heath Road in London and Hanley Library in Stoke-on-Trent, and other SPC trench heating projects include The Grand York Hotel, The Orangery at Aynho Park, Berkhamsted Sixth Form, the Museum of Two Halves in Wrexham, Archway Tower in London and the Midlands Goods Shed at King’s Cross. See SPC’s projects.
Metropolitan Natural Trench Heater specification summary
| Detail | Spec |
|---|---|
| Type | Natural convection LTHW trench heater, no fans |
| Widths | 150, 225 or 300 mm (width at feet 200, 275 or 350 mm) |
| Heights | 90, 145 or 200 mm |
| Lengths | 24 standard lengths from 800 to 3,100 mm in 100 mm steps; longer runs joined with flangeless end plates |
| Heat output | 120 to 2,388 W per unit at 80/60°C water and 20°C room air (ΔT 50°C), depending on width, height and length |
| Heat exchanger | Copper tubes expanded into aluminium fins, in galvanised sheet steel tubeplates, with a vent plug; pressure tested to 22 barg, air under water |
| Water connections | 15 mm plain copper, front or side entry |
| Casing | Minimum 1.2 mm mild steel, black powder coat, with knock-outs for pipework and cables, levelling screws at all four corners, adjustable support feet, transverse bracing and a protective cover |
| Grilles | Anodised aluminium roll-up grille with stainless steel springs and plastic spacers, 60% free area, with matching trim; stainless steel grilles on request |
| Grille finishes | Satin silver, black and a range of Anolok bronze, gold, umber and blue-grey colours |
| Floors | Screeded (concrete) or suspended floors |
| Controls | Water side: 2-port valves and actuators, wall mounted room thermostats, and flexible hoses with integral isolating valves |
| Bespoke options | Bespoke widths, heights and lengths, curved sections and grilles, corner kits with angled sections and mitred corner grilles |
| Testing | Independently tested to BS EN 164301 |
| Manufactured | Leicester, UK, by S & P Coil Products Limited (ISO 9001:2015) |
1 EN 16430: European performance test standard for trench convectors and fan assisted convectors.
Full heat output and water pressure drop data for every width, height and length is in the Metropolitan Trench Heating and Cooling brochure.
Discuss your trench heating project
Send us your layout for a Metropolitan Natural Trench Heater selection for your office, school, hotel, library or public building, request a site survey or book the Trench CPD. Call +44 (0)116 249 0044, email spc@spc-hvac.co.uk or use the form below.
Frequently Asked Questions
Natural trench heaters, such as Metropolitan Natural Trench Heaters, have no fans: air moves through the heat exchanger by natural convection alone. Fan-assisted trench heaters use crossflow fans to move air through the heat exchanger. SPC makes both types, including Metropolitan Powered Units and Metropolitan HC trench heating and cooling, and can advise which suits your project.
Yes. LTHW (low temperature hot water) and LPHW (low pressure hot water) both describe the wet heating systems Metropolitan Natural Trench Heaters connect to. SPC’s trench literature uses LPHW, and publishes Metropolitan Natural outputs at 80/60°C water and 20°C room air.
No, the trench heater itself has no fans or electrical parts. A power supply is only needed for an actuator and room thermostat where the hot water is controlled by a 2-port valve. If the unit is set in a screeded floor, any conduit for that wiring must be in place before the screed is laid.
Metropolitan Natural Trench Heater roll-up grilles are suitable for occasional foot traffic. They should not take point loads such as chair legs, and trench heaters should not be fitted directly in front of doorways or in areas of constant footfall, where there is a risk of damage and debris from footwear.
Install Metropolitan Natural Trench Heaters close to the window or wall they protect, with the heat exchanger on the window side and the flow and return pipework on the left hand side when looking from inside to outside. IOM 76 gives the recommended distances from the glazing and the clearances needed around the casing in a screeded floor.
Roll up the grille to reach the inside of the casing. Clean the heat exchanger with a vacuum cleaner or compressed air, more often in dusty areas, and wipe the casing and grille with a dry or damp cloth and mild detergent. The heating water should be treated with an inhibitor that is compatible with copper. Full guidance is in IOM 76.
Yes. A Metropolitan Natural Trench Heater BIM object is free to download from SPC on bimstore. Dimensional drawings for every width and height are in the brochure.
