What Is TOG Rating and How Do I Know If My Floor Is Compatible With Underfloor Heating?

If you are planning an underfloor heating system or you already have one installed, you will almost certainly come across the term TOG. It appears on carpet labels, underlay packaging, and in the technical guidance issued by most underfloor heating manufacturers. Yet despite how often it comes up, many homeowners are unsure what it actually means or why it matters.

This guide explains the TOG rating clearly, covers how different flooring types are affected, and tells you how to check whether the floor you are considering will work well with an underfloor heating system.

What Does TOG Mean?

TOG is a unit of thermal resistance. It measures how effectively a material resists the flow of heat through it. The higher the TOG value, the more the material insulates against heat transfer.

The word itself comes from a colloquial British term for clothing, and the measurement was originally used to rate the warmth of duvets. It has since been adopted across the flooring and heating industries as a standard way to describe how much a floor covering will impede heat rising from below.

One TOG is defined as the resistance to heat flow that allows a temperature difference of 0.1 degrees Celsius for every watt of heat flowing through one square metre. In practical terms, a high-TOG floor acts like a blanket placed over your heating system, trapping warmth beneath the surface rather than letting it into the room.

Why Does TOG Rating Matter for Underfloor Heating?

Underfloor heating works by warming the floor surface and allowing that warmth to radiate upward into the room. The floor covering sits directly between the heat source and the living space, which means its thermal resistance has a direct impact on the system's efficiency.

If the TOG value of the floor covering is too high, the heating system has to work harder and run at higher temperatures to achieve the same room temperature. This increases energy consumption, can shorten the lifespan of the system, and in some cases may lead to the floor surface temperature exceeding safe limits for the materials involved.

Keeping the combined TOG of your floor covering within the recommended threshold ensures your system heats the room efficiently, operates within safe surface temperatures, and uses energy economically.

What Is the Maximum TOG Rating for Underfloor Heating?

The generally accepted industry limit for flooring used over an underfloor heating system is a combined TOG value of 2.5, though many manufacturers and installers recommend staying at or below 2.0 to give the system the best working conditions.

That combined value includes both the floor covering and any underlay. So if your carpet is rated at 1.5 TOG and your underlay is rated at 1.0 TOG, the combined resistance is 2.5 TOG, which sits at the upper limit. Exceeding this threshold is one of the most common reasons underfloor heating systems underperform.

It is worth noting that some electric underfloor heating systems may have slightly different tolerances, so it is always worth checking the specification of your particular installation.

How Do I Check the TOG Rating of My Flooring?

For carpets and underlays

Most carpets and underlays sold in the UK are tested and labelled with a TOG rating. You can usually find this information on the product packaging, the manufacturer's website, or on the product specification sheet available from the retailer.

When buying carpet for use over underfloor heating, look for products specifically labelled as suitable for use with underfloor heating. These will typically carry a TOG rating of 1.5 or less, leaving room for an appropriate underlay without breaching the combined threshold.

For hard flooring

Tiles, stone, engineered wood, luxury vinyl tile (LVT), and laminate are generally low in thermal resistance and work well with underfloor heating. Unlike carpet, these materials are rarely given a TOG value on their specification sheets because their resistance is low enough that it rarely causes problems.

Solid hardwood flooring is a different matter. It tends to have a higher natural thermal resistance than engineered alternatives and can also be prone to movement when exposed to heat. It is not recommended for use over underfloor heating for this reason.

Using a TOG calculator

If you are unsure whether your flooring choice is suitable, a simple compatibility check can help. Our blog post on best flooring options for underfloor heating in renovation projects includes a warmth calculator you can use to estimate how different floor types will perform over an underfloor heating system. It is a useful first step before committing to a particular material.

TOG Ratings by Flooring Type

Here is a general guide to how common flooring types compare in terms of thermal resistance:

• Ceramic and porcelain tiles: Extremely low thermal resistance. The best-performing option for underfloor heating. Heat passes through quickly and evenly.

• Natural stone: Similarly low resistance to tiles. Excellent heat distribution and a high-end finish.

• Luxury vinyl tile (LVT) and vinyl: Thin and low resistance. One of the most practical choices for rooms with underfloor heating.

• Engineered wood: Good compatibility. Heat distribution is slightly slower than tiles but well within acceptable limits. Always check the manufacturer's maximum floor temperature guidance.

• Laminate: Generally compatible, with similar performance to engineered wood. Choose products labelled as suitable for underfloor heating.

• Carpet: Compatible only when the combined TOG of the carpet and underlay does not exceed 2.5. Low-TOG carpet and a purpose-made underlay are required for the system to work effectively.

• Solid hardwood: Generally not recommended. Higher thermal resistance and a tendency to warp or gap when exposed to heat make it unsuitable for most underfloor heating systems.

Can I Use Underlay With Underfloor Heating?

Yes, but the choice of underlay matters significantly. A standard cushion-backed underlay can have a TOG value of 2.0 or more on its own, which would push you well over the combined threshold before the carpet is even factored in.

Purpose-made underlays for use with underfloor heating are designed to have a low thermal resistance, typically around 1.0 TOG or below. These allow heat to pass through while still providing the acoustic benefits and underfoot comfort that underlay is intended to deliver.

If you are in any doubt, look for underlays that carry a specific underfloor heating compatibility label and check the TOG value before purchase.

What Happens If the TOG Is Too High?

If your floor covering exceeds the recommended TOG limit, you are likely to notice a few things. The room may take considerably longer to reach a comfortable temperature. The heating system may need to run at a higher output than it was designed for, increasing your energy bills. Over time, this can also place unnecessary strain on the system.

In some cases, running a system harder than intended to compensate for a restrictive floor covering can cause the heating elements to overheat, which may shorten their lifespan or, in the worst case, trigger a thermal cut-out and leave you without heating entirely.

Getting the flooring right from the outset is far less costly than replacing either the floor covering or the heating system after the fact.

TOG and Underfloor Heating Efficiency

One of the key benefits of underfloor heating over traditional radiators is that it operates at a lower water or surface temperature to achieve the same level of room warmth. This makes it inherently more efficient, particularly when paired with heat pump systems.

Choosing a low-TOG floor covering helps preserve this efficiency advantage. The lower the thermal resistance of the floor, the less energy is required to bring the room to the desired temperature, and the more consistent and comfortable the warmth underfoot.

For those looking to maximise the efficiency of their system, tiles or stone over underfloor heating with no additional underlay represent the optimal combination. Where comfort or aesthetics require a softer finish, LVT or low-TOG carpet with a compatible underlay offer the best balance.

What If I Have Underfloor Heating Already Installed?

If your underfloor heating system is already in place and you are planning to change the floor covering, the same TOG principles apply. You should check the TOG rating of any new carpet or underlay before installation, and confirm that the combined value falls within the limits specified by your system's manufacturer.

If you are replacing a hard floor covering with carpet, this is the most common situation where problems arise. What worked perfectly with tiles may struggle under a thick carpet, so it is worth taking the time to choose a low-TOG option even if the installation looks straightforward.

If you are unsure whether your existing system is performing as it should, or if you are considering a change of floor covering and want to be certain the heating will still work effectively, speaking with an experienced installer is the most reliable way to get the right answer for your specific setup.

Talk to Comfort Floors

Comfort Floors has more than 25 years of experience designing and installing bespoke underfloor heating systems for domestic and commercial clients. Whether you are starting a new build, renovating an existing space, or simply trying to get more from a system that is already in place, the team can advise on flooring compatibility, system design, and everything in between. All consultations begin with a free site visit and no-obligation quotation.

To get in touch, visit comfort-floors.co.uk/contact or call 01908 562211.