The ThermoSphere Ultimate Low Output is a loose-lay electric underfloor heating cable purpose-built for homes with a restricted electrical load supply or properties that need to manage circuit capacity carefully. It uses the same proven TwistedTwin cable construction and in-line joint technology as the standard ThermoSphere Ultimate cable, but delivers a gentler 57W/m² or 85W/m² output instead of the standard 130W/m² or 195W/m² range.
This makes it the natural choice for well-insulated new-build properties, homes running on a limited single-phase supply, or installations designed to run primarily from self-generated solar electricity and battery storage, where keeping instantaneous electrical draw low matters as much as keeping the floor warm. Like the standard Ultimate range, it installs into ThermoSphere Membrane or Self-Adhesive Membrane with no cutting into the membrane or subfloor required.
In-Line Joint
No Cuts Required
ℹ️ Designed for Restricted Load Supplies
ThermoSphere Ultimate Low Output is built for homes with a restricted load supply or properties that need to manage electrical demand carefully. It is compatible with self-generated solar electricity and battery storage systems, making it a strong fit for low-heat-loss, well-insulated properties where minimising instantaneous draw matters.
⚠️ Lower Output Than Standard Ultimate Cable
This is a genuinely different output tier from the standard ThermoSphere Ultimate cable range. Standard Ultimate delivers 130W/m² or 195W/m²; the Low Output version delivers 57W/m² or 85W/m² — roughly 44% of the standard output at the same stud spacing. Always confirm the room's heat-loss calculation supports this lower output before specifying, particularly if the cable is intended as a primary heat source rather than a supplementary comfort heat.
In-Line Joint — No Cutting Into the Floor
The cable's in-line joint is the same diameter as the cable body throughout — it presses flat into the membrane's stud channel with no groove needing to be cut. This keeps the membrane's waterproofing layer completely intact and removes a common point of installation damage.
TwistedTwin Cable — Stress-Free, Fully Earthed
ThermoSphere's proprietary TwistedTwin cable uses a twisted-pair conductor construction that neutralises mechanical stress under repeated thermal cycling. A continuous full earth braid runs the entire cable length for consistent electrical safety.
Selectable Output — 57W/m² or 85W/m²
Output is set purely by stud spacing in the membrane: 3-dimple spacing gives 57W/m², 2-dimple spacing gives 85W/m². No tools or extra accessories are needed to change the output — just vary the routing pattern.
Built for Restricted Electrical Loads
Lower per-square-metre draw makes this cable a practical fit for properties on a limited supply capacity, or where the design intent is to run heating primarily from solar generation and battery storage rather than continuous grid draw.
Extra Heavy Use — Robinson Test Rated
Rated for extra heavy use under the Robinson Test, the industry benchmark for cable durability under concentrated loading. Withstands heavy furniture, foot traffic, and tile installation without damage.
Compatible With All Decoupling Membrane Brands
Optimised for ThermoSphere Membrane Mats but compatible with all decoupling membrane brands. Installers with a preferred membrane can retain it while specifying this cable.
IP68 — Safe in Wet Rooms and Bathrooms
IP68 rated — fully impervious to moisture, safe for use in wet rooms, shower areas and bathrooms when installed with appropriate waterproofing accessories.
Lifetime Warranty — Stays With the Property
Backed by a lifetime warranty when registered online. The warranty transfers with the property on sale — new owners remain covered.
Technical Data
| Voltage |
230V / 50Hz |
| Output (3-stud spacing) |
57 W/m² |
| Output (2-stud spacing) |
85 W/m² |
| Membrane Thickness |
5.5mm |
| Cable Lengths |
12m to 200m |
| Cable Insulation |
FEP and HR-PVC |
| Protection Rating |
IP68 |
| Robinson Test Rating |
Extra heavy use |
| Recommended Max Floor Temperature |
27°C (limited by thermostat controls) |
| Joint Type |
In-line (same diameter as cable body — no membrane cuts required) |
| Warranty |
Lifetime (online registration required) |
| Cable Country of Origin |
India |
| Membrane Country of Origin |
Italy |
| SKU |
Cable Length |
Area @ 57W/m² |
Area @ 85W/m² |
Output (W) |
EAN |
| HDMC-5-012 |
12m |
1.2 m² |
0.8 m² |
68W |
5056257309507 |
| HDMC-5-018 |
18m |
1.7 m² |
1.2 m² |
102W |
5056257309514 |
| HDMC-5-025 |
25m |
2.3 m² |
1.5 m² |
128W |
5056257309521 |
| HDMC-5-031 |
31m |
2.9 m² |
1.9 m² |
162W |
5056257309538 |
| HDMC-5-037 |
37m |
3.5 m² |
2.3 m² |
196W |
5056257309545 |
| HDMC-5-050 |
50m |
4.6 m² |
3.1 m² |
264W |
5056257309552 |
| HDMC-5-061 |
61m |
5.8 m² |
3.8 m² |
323W |
5056257309569 |
| HDMC-5-075 |
75m |
6.9 m² |
4.6 m² |
391W |
5056257309576 |
| HDMC-5-100 |
100m |
9.2 m² |
6.2 m² |
527W |
5056257309583 |
| HDMC-5-125 |
125m |
11.5 m² |
7.7 m² |
655W |
5056257309590 |
| HDMC-5-150 |
150m |
13.8 m² |
9.2 m² |
782W |
5056257309606 |
| HDMC-5-200 |
200m |
18.5 m² |
12.3 m² |
1046W |
5056257309613 |
⚠️ Qualified Electrician Required
All electrical connections must be made by a qualified electrician in accordance with BS 7671. Register your product with ThermoSphere online after installation to activate the lifetime warranty.
Frequently Asked Questions
What makes this different from the standard ThermoSphere Ultimate cable?
The standard Ultimate cable delivers 130W/m² or 195W/m². This Low Output version delivers 57W/m² or 85W/m² — designed specifically for restricted load supplies and low heat-loss properties, rather than as a direct primary heat source in higher heat-loss rooms.
Which membrane do I use with this cable?
Designed for ThermoSphere Membrane Mats but compatible with all decoupling membrane brands.
What outputs can I achieve?
57W/m² at 3-stud spacing, or 85W/m² at 2-stud spacing. No tools or extra parts are needed to switch between the two — output is set entirely by how the cable is routed through the membrane.
Is this cable suitable as a primary heat source?
It can be, but only where the room's heat-loss calculation supports the lower output — typically well-insulated new-build properties. For higher heat-loss rooms such as bathrooms, conservatories, or older solid-wall properties, the standard 130W/m² or 195W/m² Ultimate cable is usually the better fit.
What lengths are available?
12m to 200m across twelve cable sizes, sized to suit areas from around 0.8 m² up to 18.5 m² depending on the stud spacing used.
Can the cable be cut?
No — never cut the heating cable. Select the cable length that matches your area at your chosen output before purchase.
