How Does Floor Insulation Affect Underfloor Heating Performance?

Underfloor heating systems provide exceptional comfort and high energy efficiency when properly designed. However, one of the most critical factors determining system efficiency—floor insulation—is often overlooked.

Insufficient or incorrectly applied floor insulation:

• Increases heat losses

• Raises energy consumption

• Causes slow heating and rapid cooling of the system

In this article, we examine the impact of floor insulation on underfloor heating performance from both a technical and practical perspective. We also cover insulation materials, correct thickness selection, and explain how floor insulation works as an integrated system with KAS Therm underfloor heating solutions.

1. What Is Floor Insulation and Why Is It Necessary?

Floor insulation is a thermal insulation layer applied to reduce heat loss toward lower layers such as concrete slabs, screed, soil, parking areas, or unheated spaces.

In underfloor heating systems, the primary objective is to ensure that the generated heat:

• Is directed upward into the living space

• Has minimal loss downward or sideways

Without adequate insulation beneath the system, a significant portion of the heat emitted from underfloor heating pipes is lost to lower layers. This reduces system efficiency and increases energy bills.

2. Impact of Floor Insulation on Underfloor Heating Performance

The effect of floor insulation on underfloor heating performance can be evaluated under three key aspects:

Reduction of Heat Loss

In poorly insulated or uninsulated floors:

• A large portion of generated heat escapes downward

• Reaching the desired room temperature takes longer

• Boilers, heat pumps, or heating sources must operate longer

With proper insulation:

• Heat is primarily directed upward

• Comfortable temperatures are reached more quickly

• Energy consumption is significantly reduced

Effect on System Response Time

Floor insulation also affects how quickly the system heats up and cools down.

• Poor insulation leads to slower response and sluggish system behavior

• Well-insulated floors allow faster and more controlled heat transfer

This directly improves both comfort and energy efficiency.

System Sizing and Capacity Calculation

High heat losses require:

• More pipe length

• Higher water temperatures

• More powerful heat sources

This increases both initial investment costs and long-term operating expenses.

With proper floor insulation, underfloor heating systems can be designed with lower capacities, providing substantial long-term cost advantages.

3. Common Floor Insulation Materials Used in Underfloor Heating

The most commonly used insulation materials include:

EPS (Expanded Polystyrene)

• Low thermal conductivity

• Lightweight and easy to install

• Available in various densities and thicknesses

• Widely used in underfloor heating projects

XPS (Extruded Polystyrene)

• Lower water absorption than EPS

• High compressive strength

• Ideal for ground-contact and subfloor applications

Polyurethane (PUR/PIR) Boards

• Excellent insulation performance

• Effective even at thin thicknesses

• Higher cost compared to EPS/XPS

Material selection should consider project type, load-bearing requirements, moisture exposure, and budget.

4. Insulation Thickness and Proper Application

Insulation thickness has a direct impact on underfloor heating performance.

General guidelines:

• Residential projects: 3–5 cm

• High heat-loss areas: 5–8 cm

• Ground-contact or unheated spaces: thicker insulation recommended

Incorrect thickness selection:

• Too thin → increased heat loss

• Excessively thick → architectural level and height issues

The correct approach is to determine insulation thickness through project-specific heat loss calculations.

5. Relationship Between Floor Coverings and Insulation

Floor coverings also affect system performance and must be evaluated together with insulation.

• Ceramic tiles, granite, and stone: high thermal conductivity, ideal for underfloor heating

• Wood and laminate flooring: lower conductivity; manufacturer certification for underfloor heating compatibility is required

• Carpets: slow heat transfer; system temperature and capacity must be adjusted accordingly

Correct insulation combined with appropriate floor coverings maximizes underfloor heating efficiency.

6. Floor Insulation in KAS Therm Underfloor Heating Systems

KAS Therm underfloor heating systems are designed based on a system integrity principle, not just high-quality pipes and components. Proper floor insulation is a core part of this approach.

Upward Heat Flow Optimization

When KAS Therm PE-RT and PEX pipes are used together with suitable floor insulation:

• Heat energy is directed upward into the living space

• Downward heat loss is minimized

• High efficiency is achieved even at lower water temperatures

Project-Specific Insulation Recommendations

The KAS Therm engineering team evaluates:

• Climatic conditions

• Characteristics of the lower floor (parking area, void, soil contact, etc.)

• Floor covering type

• Heat loss calculations

to recommend the ideal insulation material and thickness for each project.

Energy Efficiency and Comfort

With proper insulation, KAS Therm systems:

• Reach target temperatures faster

• Reduce energy bills

• Provide uniform surface temperatures for superior comfort

7. What Happens Without Floor Insulation?

In underfloor heating systems without proper insulation, the following issues may arise:

• High energy consumption

• Delayed comfort levels

• Unnecessary heating of lower layers

• Operation at higher temperatures

• Reduced lifespan of boilers or heat pumps

In short, without insulation, underfloor heating systems cannot reach their full efficiency potential.

8. Key Points to Consider During Installation

When applying floor insulation in underfloor heating systems, attention should be paid to:

• No gaps between insulation boards

• Use of suitable pipe-support systems (insulated panels, mesh-supported layers, etc.)

• Pressure testing before screed application

• Floor level planning that accounts for insulation, pipes, and screed thickness

KAS Therm systems support these steps with detailed technical documentation and installation guidelines.

Efficient Underfloor Heating Is Not Possible Without Proper Floor Insulation

Regardless of the pipe, manifold, or heat source used, underfloor heating performance will never reach optimal levels without proper floor insulation.

Correct insulation:

• Minimizes heat loss

• Reduces energy consumption

• Improves system response time

• Lowers long-term operating costs

When combined with high-quality components and proper insulation solutions, KAS Therm underfloor heating systems deliver outstanding results in both energy efficiency and thermal comfort.

To determine the most suitable underfloor heating and floor insulation combination for your project, you can contact the KAS Therm expert team.

With the right insulation, the right system, and the right application, the true performance of underfloor heating can be fully realized.