Key Takeaways
- Radiant heat subflooring provides an efficient way to distribute heat evenly across rooms, enhancing overall comfort.
- Several subflooring options exist, such as concrete slabs and plywood overlays, each with its unique benefits and considerations.
- The choice of subfloor type will be influenced by the flooring material (e.g. hardwood, vinyl, laminate) and the installation process.
What is Radiant Heat Subflooring?
Integrated radiant heat subflooring refers to the foundational structure onto which you install your radiant floor heating systems (beneath the flooring).
Unlike traditional heating systems that heat the air (like forced air systems), radiant heat systems warm up the floor itself, which in turn heats the objects and people in the room.
The principle behind this is the direct transfer of heat from the warm surface to cooler objects in contact with or close to it.
Here’s a breakdown:
The Different Types of Subflooring
The different types of subflooring will largely be determined by the type of flooring you intend to use, whether you will use radiant floor heating under carpet, tiles, hardwood or vinyl, for example. This is in conjunction with other typical factors like how much you want to spend.
Concrete, 5/8” plywood or oriented strand board (OSB) are generally considered as the best subfloor materials for indoor radiant heating systems.
Concrete Slab
Common for hydronic systems. The tubes which carry the heated water solution are embedded in a wet concrete slab, which, when cured, acts as an excellent thermal mass.
This type of subfloor retains heat effectively and releases it slowly, ensuring an efficient system.
Plywood and Gypsum Overlays
For both hydronic and electric systems. The heating elements are placed over an existing subfloor, then covered with a layer of gypsum or thin-set mortar.
For wooden subfloors, a layer of plywood may be added first for stability.
OSB
For both hydronic and electric systems.Its denser composition makes it a good choice for radiant heat systems..
Tongue-and-Groove Panels
These are specialized panels with grooves or channels for radiant heating tubes.
They can be made from plywood, OSB, or other materials and are designed for easy installation.
Pros and Cons of the different types of subflooring
Concrete Slab
Pros:
- High Thermal Mass: Concrete retains and releases heat slowly, providing consistent and prolonged warmth, suitable for both electric and hydronic systems.
- Durability: Once set, concrete is long-lasting and requires minimal maintenance.
- Ideal for Basements or Ground Floors: Being a heavy material, it's especially suited for ground-level installations.
Cons:
- Longer Heat-Up Time: Due to its high thermal mass, it can take longer for the floor to initially heat up.
- Potential for Cracking: Over time, concrete can develop cracks which may affect the heating tubes or cables.
- Weight: The added weight of concrete may not be suitable for all structures, especially upper-level installations.
Plywood and Gypsum Overlays
Pros:
- Versatility: Can be used with both electric and hydronic systems.
- Quicker Response Time: These materials don't have the high thermal mass of concrete, so they heat up and cool down faster.
- Easier Retrofit: Easier to install in existing homes as a retrofit than pouring a new concrete slab.
Cons:
- Lesser Heat Retention: They don't hold onto heat as long as concrete does.
- Potential for Uneven Heating: If not installed correctly, there might be spots that are warmer or cooler than others.
OSB
Pros:
- Excellent for electric systems but can be used with hydronic.
- Strong and durable.
- Generally less expensive than plywood.
Cons:
- Can swell if exposed to water for extended periods.
- Edges might fray over time if not properly protected.
Tongue-and-Groove Panels
Pros:
- Interlocking design provides a tight seal.
- Helps to prevent squeaking and movement.
- Provides a smooth and even surface for finish flooring .
Cons:
- Typically more expensive than standard plywood or OSB.
- Incorrect installation can lead to gaps or misalignments.
What is the best subfloor for Radiant Heat?
Understanding the optimal subfloor for each type of flooring is crucial for ensuring the longevity and efficiency of your radiant heat system.
OSB and plywood are generally held to be among the best materials for radiant heat system subfloors, but it is important to also factor in the type of flooring that will sit above your in-floor heating system.
Below is a table that shows which type of subfloor goes best with easy type of common flooring material:
| Type of Flooring | Best Suited Subfloor for Radiant Heating | Reason/Notes |
|---|---|---|
| Hardwood | Subfloor Panels/Tongue-and-Groove Panels | Ensures even heat distribution without warping the wood. |
| Vinyl | Plywood and Gypsum Overlays | Provide a smooth, consistent base; important to prevent vinyl from forming bumps or ridges. |
| Laminate | OSB | Ensure stability and even heat distribution, crucial since laminate can be sensitive to temperature changes. |
| Tile | Concrete | Offers excellent heat retention and stability, crucial for preventing tile cracks. |
| Carpet | Plywood and Gypsum Overlays or Subfloor Panels | Good for even heat, but ensure sufficient insulation to prevent the carpet from becoming overly warm. |
What About Radiant Floor Heating on a Wood Subfloor?
Radiant floor heating can be installed on a wood subfloor, but there are specific considerations and methods to ensure the system operates efficiently and safely. Wood is a natural material that can expand and contract with temperature fluctuations, so it’s essential to ensure that the radiant heating doesn’t damage or warp the wood.
Types of Wood Subfloors:
- Plywood: Common in many homes, it provides a stable base for both the heating system and the flooring material.
- OSB (Oriented Strand Board): Another common type of wood subfloor, it’s slightly denser than plywood.
- Tongue–and–Groove: This can be made from plywood or other types of wood and provides a tight interlocking system.
Considerations for Radiant Heating on Wood Subfloors:
- Thermal Conductivity: Wood has lower thermal conductivity than materials like concrete. This means the heat might not spread as quickly or evenly. Using a system designed for wood subfloors can help address this issue.
- Expansion and Contraction: Wood expands and contracts with temperature changes. A too-rapid temperature change can cause warping or cracking. Therefore, the heating system should heat gradually.
- Moisture Content: Wood can be affected by moisture. Ensure that the wood subfloor’s moisture content is suitable before installation. Also, the use of a vapor barrier might be necessary to prevent moisture from reaching the wood from below.
Installation Methods
Above the Subfloor
Many hydronic systems, particularly those in retrofit scenarios, will place the tubing above the wood subfloor.
This could be within lightweight concrete, specialized panels, or thin-set mortar. Electric radiant mats or cables can be laid directly onto the wood subfloor.
Between Joists
If you have access from below, such as in a basement or crawl space, hydronic tubing can be installed between the joists under the wood subfloor.
It’s essential to use aluminum heat transfer plates for even heat distribution and to insulate beneath the tubes to direct heat upwards.
How to Make Subflooring for Radiant Heat Systems
Regardless of the subflooring type or system (electric vs. hydronic), proper installation begins with a well-insulated base, ensuring upward heat movement.
For hydronic systems, tubing needs to connect to a manifold, which then connects to the boiler or water heater.
Electric systems require careful layout of the heating mats or cables, ensuring no overlapping, followed by connection to thermostats and the main power supply.
Always conduct pressure tests for hydronic systems or resistance tests for electric systems before sealing the subfloor to ensure there are no leaks or breaks.
Below is a step by step guide to installing both the subflooring and the radiant heating system.
- Plan and Design: Determine the layout of the heating system and ensure that the chosen subflooring material is compatible with radiant heating.
- Prepare the Base Floor: Clean the base floor, ensuring it’s free from debris and moisture.
- Install insulation, typically EPS (Expanded Polystyrene) or XPS (Extruded Polystyrene), to prevent heat loss downwards.
- Lay the Heating Element: For hydronic systems, lay out the tubes. For electric systems, place the electric coils or lay the radiant heat mats. Ensure even spacing for consistent heating.
- Install the Subflooring: Depending on the type chosen (Plywood, OSB, Concrete Backer Board, or Two-layer), follow the manufacturer’s guidelines. Ensure a flat and smooth surface.
- Test the System: Before installing the final flooring, test the radiant heating system to ensure even heating and correct functionality.
- Install the Final Flooring :Lay down the chosen flooring material (tile, wood, carpet, etc.) over the subflooring. Ensure the flooring material is suitable for radiant heat systems
Should Radiant Heat go Above or Below the Subfloor?
Whether radiant heat should go above or below the subfloor is a question that often arises during the planning stages of radiant heating system installations.
The answer largely depends on the type of radiant heat system (hydronic or electric) and the specific conditions of the project.
Here’s a breakdown:
Hydronic Radiant Heat Systems
Below the Subfloor
In many traditional hydronic installations, the tubing is placed beneath the subfloor, between the joists.
When installed this way, it’s essential to have aluminum heat transfer plates that distribute the heat evenly across the width of the joist bay.
Reflective insulation is also often placed below the tubing to direct the heat upwards.
Pros:
- This method allows for retrofitting radiant heating into existing structures without disturbing the existing floor.
- It does not raise the floor height.
Cons:
- Heat transfer can be less direct than systems installed above the subfloor, possibly resulting in slightly less efficiency.
- The installation can be more labor-intensive, requiring access to the joist bays from below.
Above the Subfloor
The tubing can also be embedded in a concrete slab or lightweight concrete over the subfloor, or within specialized panels that sit on top of the subfloor.
Pros:
- Provides more direct heat transfer to the floor surface, which can be more efficient.
- The thermal mass of the concrete can provide consistent, even heating.
Cons:
- Adds significant weight to the structure, so the structural integrity must be considered.
- Raises the floor height, which might affect transitions to other rooms and door clearances.
Electric Radiant Heat Systems
Above the Subfloor
Most electric radiant systems are designed to be installed directly above the subfloor and below the finish flooring.
They are usually thin and don’t significantly raise the floor height.
Pros:
- Direct contact with the finish flooring ensures efficient heat transfer.
- Simple and faster installation compared to many hydronic systems.
Cons:
- Without proper insulation below, there's potential for heat loss downwards.
Summary
For hydronic systems, the choice of placing the tubing above or below the subfloor often depends on the specific project conditions, such as whether it’s a new construction, a retrofit, structural considerations, and desired efficiency.
For electric systems, the heating elements are typically placed above the subfloor, directly below the finish flooring, for optimal heat transfer.
In all cases, proper insulation and heat distribution measures should be in place to ensure the system operates efficiently.
What about Underlayment for Radiant Floor Heating Systems?
Electric Radiant Floor Heating Systems
Electric radiant heating typically comes in the form of heating mats or cables. The choice of underlayment can significantly impact the system’s efficiency.
Underlayment Types:
Insulating Underlayment
This is made from materials like cork or dense foam.
It’s essential because it ensures the heat from the electric cables rises up into the room rather than being absorbed down into the subfloor.
It enhances efficiency by directing the heat where you want it.
Pros:
- Increases the system's efficiency.
- Can act as a sound barrier, reducing noise transmission.
- Some types can also serve as a vapor barrier.
Cons:
- Adds an additional cost to the installation.
- Can raise the height of the floor, affecting transitions to other rooms.
Standard Underlayment
These are typical underlayments without specific insulating properties. They might be made from felt or thin foam.
Pros:
- Generally more affordable than insulating underlayments.
- Can help smooth out minor subfloor imperfections.
Cons:
- Doesn't optimize the system's efficiency as an insulating underlayment would.
Recommendation
For electric systems, using an insulating underlayment is highly recommended to maximize the efficiency of the heating system.
Hydronic Radiant Floor Heating Systems
Hydronic systems use tubes to circulate hot water beneath the floor. The type hydronic radiant floor heating underlayment used can impact the system’s heat distribution and efficiency.
Underlayment Types:
Thermal Mass UnderlaymentMaterials like thin-set mortar or self-leveling cement can be used. They encapsulate the tubes and create a thermal mass that holds and distributes the heat.
Pros:
- Provides excellent heat distribution across the floor.
- Increases system efficiency by holding and releasing heat steadily.
Cons:
- Can be more labor-intensive to install.
- Adds weight to the floor.
Insulating Panels
Radiant heat subfloor panels are specifically designed (often made of foam or other insulating materials) with channels or grooves to hold the hydronic tubes in place.
Pros:
- Provides a level of insulation, directing heat upwards.
- Easier and quicker to install than thermal mass underlayments.
Cons:
- Might be more expensive than traditional underlayments.
- Not as efficient in heat retention as thermal mass underlayments.
Recommendation
For hydronic systems, the choice between thermal mass underlayment and insulating panels often depends on the specific project needs.
For new constructions or when adding a new subfloor, thermal mass underlayments are a great choice.
For retrofitting in existing spaces where adding weight or height might be an issue, insulating panels can be more suitable.
FAQs
What tools do I need to install a subfloor for a radiant heating system?
For a radiant heat subfloor installation, you’ll typically need a tape measure, utility knife, straight edge, trowel (for applying thin-set or adhesive), staples or screws (depending on the material), and a staple gun or drill.
If you’re installing tubing for a hydronic system, tube cutters and connectors may also be necessary.
Always refer to the manufacturer’s instructions, as specific tools might vary based on the subfloor material and type of radiant heating system.
How do I ensure even heat distribution across my subfloor?
Even heat distribution is crucial for comfort and the longevity of your flooring.
When installing the radiant heating system, ensure that the heating tubes or cables are spaced consistently, according to the manufacturer’s recommendations.
Using subfloor panels with pre-set channels or grooves can help maintain uniform spacing.
It’s also essential to choose a subfloor material that complements the type of flooring to ensure optimal heat conduction and retention.
Can I retrofit my existing floors with a radiant heating system, or do I need a new subfloor?
It is possible to retrofit existing floors with radiant heating, but it often requires adding a new subfloor layer or overlay to accommodate the heating elements.
This addition might raise the floor height, so transitions to other rooms and door clearances should be considered.
Plywood and gypsum overlays are commonly used for retrofitting because they can be applied over the existing subfloor.
Always consult with a professional to determine the best approach for your specific situation.
Conclusion
Under subfloor radiant heat revolutionizes home heating by offering a more efficient and comfortable alternative to traditional methods.
When chosen and installed correctly, this system can provide consistent warmth while potentially reducing energy costs.
The key is selecting the right subfloor that complements the flooring type, ensuring both durability and optimal heat distribution.
As with any home improvement project, research, proper planning, and professional consultation can make all the difference. Whether you’re retrofitting an existing space or building a new one, integrating radiant heat subflooring can elevate your home’s comfort and value for years to come. Get a quote for your bespoke system now.
