FAQ for Radiant Floor Heating

Q. How much insulation should be installed in conjunction with radiant floor heating?

Some applications of radiant floor heating require more insulation than others and some may not require any. If the radiant floor system that you are installing or having installed is part of the building envelope, like a basement concrete floor or garage concrete floor, then it is imperative that the proper amount of insulation is installed so that the radiant floor system can function efficiently.

In the southwestern region of Ontario, Canada, the Ontario Building Code (OBC) requires R10 insulation to be installed with radiant floor heat systems. The rate at which heat moves out of a building depends on a couple of variables. The first variable is the delta between the inside and outside temperature, and the second variable is how well the rest of the structure is insulated. Many professionals agree that the more insulation you have in the building, including walls and ceilings, the more you should put in the ground. After all, the ground is a part of the building envelope.

Many people will install more than the standard R10 in an effort to isolate the ground from the radiant heat source, forcing more heat upwards. Remember, hot air may rise, but heat moves from hot to cold; therefore, the more you insulate the rest of your home or commercial building, the more heat you force to the lesser insulated areas, which typically include windows and concrete slabs. The more insulation you put under the floor slab, the less heat goes into the ground.

If radiant heating is installed on a floor system that has leaving space below it, the insulation is not as critical, but it still is a good idea to isolate it as best as possible so you can maintain effective zoning. Insulating these radiant floor areas may also help with sound and acoustics.

Q. What systems are available to heat poured basement slabs? 

There are primarily two types of radiant floor heating that can be installed into concrete: electric and hydronic.

Electric Radiant Floor Heating

Electric radiant floor heating is mainly used for small areas and in retro fit construction applications. Electric radiant is installed via electric cables and mats and typically controlled in the zone it is installed.  It works well in conjunction with a forced air system that is found in many Canadian homes. Electrically heated floors are usually used for comfort purposes and are common in wood floor structures under tile floors and a good floor warmer. The downside to electric radiant floors is they typically cost more to operate than hydronic systems.

Hydronic Radiant Floor Heating

Hydronic radiant floor heating systems use a water heater or boiler and a pump system that move water through a network of tubes through the flooring system. Hydronic water heating helps the building maintain an even heat and virtually eliminates the hot and cold cycling and drafts a forced air system can create. Large heated concrete slabs become large comfortable masses of heat evenly distributing warmth to the occupants above or below. Hydronic water heat is cheaper to operate than its electrical radiant floor equivalent.

Q. Is radiant heating cheaper to operate than forced air?

There are many variables to how efficient a radiant floor heating system is and how it will compare to a forced air heating system. The main thing we need to keep in mind is it takes a certain amount of BTUs to heat a space and how efficiently you can make that BTU will determine the overall efficiency. Large hydronically heated concrete floor slabs maintain an even temperature and can often be operated at lower temperatures and maintain the same comfort as a forced air heating system at a higher temperature because it does not cycle in the same way.

The key ingredient to a comfortable and successful building is insulation and air tightness. Buildings that are insulated and air sealed properly always function more efficiently than a building that is not insulated and air sealed properly. If a hydronically heated floor system is installed in a poorly insulated building, the heating system will not be efficient. If you install a forced air system in a well-insulated building that has the floor slab insulated with rigid foam insulation or INSTA-PANELS®, the building will be comfortable and efficient.

Do not focus on the radiant floor heating system only. Also pay attention to the overall insulation of the entire building. Use higher performance insulation products, such as two pound closed cell spray foam, rigid foam board insulation, and INSTA-PANELS® floor insulation to achieve better results.

Q. If more insulation is installed under the radiant heating, do I need less radiant tubing?

The more foam insulation board or other moisture-resistant insulation material under a concrete floor slab, the more efficient the building becomes. This is no different with a hydronic heating system. The more rigid moisture-resistant the insulation, the more efficient the heating system becomes; however, this does not necessarily mean you need less radiant heat tubing. The system needs to be engineered and, in order to ensure the heat dissipates evenly, a certain amount of radiant heat tubing is required.

Size of tubing is also important when calculating the length of radiant heat tubing required.  A ½ inch tube cannot supply the same volume of heat as a ¾ inch tube; therefore, it is always important to make sure the hydronic or electric radiant floor heating system is properly engineered, insulated, and installed.

Q. What spacing should be used when installing radiant floor heating?

Spacing of hydronic tubes is dependent on a few variables, including wall R-value, window quantity, and roof or attic insulation. Consult with your radiant floor designer or engineer to determine your radiant floor requirements. It is always important to follow manufacturer’s guidelines and best practices, such as making sure there is enough heat reaching areas more susceptible to heat loss; for example, more radiant tubing will need to be installed under windows because windows are particularly vulnerable to heat loss. Windows do not provide the same thermal resistance as a properly insulated wall. As such, heat from the radiant floor is critical in helping create convection currents to move moisture and dry out stagnant air around windows.

Q. How thick should the concrete be installed over radiant heating?

The thickness of concrete is dependent on what the building code or the designer dictates. A thicker slab takes longer to warm up than a thinner slab, but it also takes the thicker slab more time to cool down. It is best practice to not install normal concrete less than three-inches thick. Thinner pours can be done on top of radiant floor heating systems. Check building plans for what is required by code. Pouring a thin set concrete or gypsum in conjunction with a radiant floor heating system is possible.

Q. How deep in the concrete should radiant tubing be installed for floor heating applications?

The placement of the radiant tubing does not affect the performance or comfort in a typical four-inch basement concrete pour. Once the slab is warm, it is easy to maintain that heat. It is common practice to raise the radiant tubing in larger and thicker concrete pours (i.e., six inch and greater).

When installing snow melt hydronic for sidewalks and driveways, it is critical to have the tubing near the top as the temperature of the glycol (not water in case it freezes) hovers around freezing so it doesn’t take as long to heat up to start melting the snow. The radiant tubes only need to go above freezing for short periods of time as its only being used to melt the snow, not heat the atmosphere. It is still very important to insulate under the concrete so that the heat from the tubes focuses on melting the snow and not warming the ground. ‎It is best to follow radiant heat manufacturer install instructions in any hydronic heat application.

Q. Is wire mesh required to install radiant tubing to all under concrete insulation systems?

There are various ways to install tubing in hydronic radiant heat applications. Hydronic tubing can be installed directly to plywood floors using a clip system or stapled directly to the plywood in conjunction with a gypsum over pour. If installing a radiant heating floor system to a concrete slab, it is critical to have the proper insulation underneath the floor heating system.

Hydronic tubing can be installed directly onto INSTA-PANELS® ‎using staples as the fiberglass skin holds the staples. As such, the tubing is installed easily and efficiently. A specialized clip system can also be installed onto INSTA-PANELS®. Once the clip system is installed, the hydronic tubing can be installed quickly. Staples and clips are common fastening methods in homes where radiant tubing is installed onto under slab concrete floors; however, wire mesh is usually required for radiant floor heating systems in a garage, shop, or engineered slab.

Concrete floor slabs in shops and garages typically carry heavier loads, which is why these concrete slabs typically get reinforced with wire mesh. The hydronic heating tubing can be fastened directly onto the wire mesh with zip ties, wire ties, or specialized tie systems with an automated tool.

The benefit of systems without wire mesh is that you save on the wire mesh cost and the labour associated with installing it. The benefit of wire mesh is it could be easier to raise the floor heating system in the radiant slab. Not all concrete slabs require wire mesh. There are fiberglass mesh reinforced concrete systems that work well in conjunction with heated floor slabs. Consult with a radiant floor heat specialist for the best option to fit your heated floor requirements and budget. It is always best to follow the hydronic radiant heat manufacturer guidelines and recommendations.

Q. How much tubing does a hydronic radiant system need to function effectively?

Installing the radiant tubing in the concrete slab is the most important step in the radiant floor heating process because it is difficult to fix a bad install once the concrete is in place. There are various tubing sizes used to create warm radiant floors. Slab size, tube spacing, heating demands, and under floor insulation are all factors that are taken into account to create a warm slab.

When a hydronic heating engineer calculates the heat load of the building, they will specify the size of tubing and length of loops from the header of the floor heating system. Larger hydronic tubing carries more heat and with potentially less resistance. By undersizing tubes or making loops too long, there is a greater possibility of cold spots in the hydronically heated floor. The tubes will release the heat in the area closest to the header and the loop coming back will be cooler. Not only will the building be cooler in certain areas but the boiler or floor heating system will not operate as efficiently as it needs to reheat the liquid from a lower temperature. It is crucial the installer of the hydronic floor heating system follows the manufacturer’s install specifications.

Q. What are the best finishes to put on top of radiant heating?

Radiant floors function most effectively with solid surface flooring. Tiles, concrete, and vinyl all work well in conjunction with a heated floor. Hardwood and laminate are also better than carpet. Flooring that does not have a resistance to thermal conductivity are the best materials to put over top of a floor heating system.

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