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Frequently asked questions about Radiant Heating

Note: Information provided by Watts Radiant, the primary radiant floor heating system that we offer.

How much should a typical radiant floor heating system cost?

System costs will vary greatly depending on the installation requirements, control choices, and project size. Simple radiant heat systems in large slabs in temperate zones cost only slightly more than the alternatives. However, if you select the many options and features that radiant can offer your home, the first cost will be higher.

Remember that the principal advantages of radiant are comfort and lower operating costs. You should review your plans and requirements with your installing contractor to get a firm price on a turn-key system.

Does a radiant heat system cost less to operate than the alternatives?

Yes they do. The amount of savings will vary depending on the heat loss, how well the structure is built, how well the building is insulated and the natural fuel source being used. For the most part radiant floors will operate anywhere from 25% to 40% more efficiently that other forms of forced air heating.

Are energy saving set-back thermostats desirable on a radiant floor heat system?

It is not recommended to use a set-back thermostat on a radiant heat system. Radiant heat systems do not respond as rapidly as a convection type heating system, mainly because a radiant floor heat system uses the mass of the building to store energy and to provide a more even heat.

What type of maintenance is required for my radiant heating system?

Most maintenance items center on the pumps and boilers. For the most part, the pumps used today are maintenance free. They use water to lubricate the bearings, which allow for more quiet, efficient life span. In general, these pumps have an estimated life span of 10 years. Most boiler installers will offer a yearly maintenance package, which includes cleaning and general up-keep. Different boiler types will require different maintenance.

What type of glycol should I use in my snow melt system?

An inhibited Propylene Glycol solution should be used. Make sure the glycol used is rated for hydronic radiant heating systems and not for automotive engines. Hydronic glycols are formulated differently for the metals seen in boilers, pumps and other system components.

How often should I check my glycol system?

Glycol systems should be checked at least once a year to ensure the system pH levels have not dropped below recommended levels. Glycol in general is acidic. The inhibitors that are added to them help neutralize the system pH, and help protect the system components. As the system ages, the inhibitors break down, causing the system pH to drop. At this point more inhibitors should be added to the radiant floor heating and snow melt systems. The system will reach a point where it will require a complete flush and re-fill. This is usually around 5-7 years, but will depend on the glycol used.

Can I use any kind of fuel source in my radiant heating system?

Any natural resource can be used to fire the heat source, natural gas, propane, electric, wood, geo-thermal, etc. It does not matter what the heat source is, as long as it can provide the necessary btu's (energy) at the required design temperatures. There will be a variance between heat sources based on efficiency, response, cost and capacity. Choose the one that bests suites the needs of the heating system.

Can I air condition my home with a radiant floor heating system?

It is not advised to try to "air condition" a space with a radiant heating system. In theory a radiant floor can be used to cool a space. In order to lower the internal temperature of a space, the cooling surface has to drop in temperature. This lower temperature "pulls" the heat from the air and is then carried away through the liquid in the tubing below the floor.

There are two main problems with this application. First, the lowered floor temperature needs to be below the room's dew point to effectively remove energy (heat) from a space. This lowered temperature will cause a layer of condensation to form on the floor surface, which may cause damage to a floor covering, not to mention creating a safety hazard. The second main reason is comfort. Our goal with any environmental control system is to maintain a higher level of comfort than what could be seen naturally. Part of this comfort level is dictated by touch. If the surface we stand on is too cool, which would be the case in a radiantly cooled home, our comfort level is severally compromised.

One note should be added here. There are systems in existence that claim to do radiant floor cooling. In fact, most of these systems are coupled with some sort of air handler to prevent the floor from condensing.

I'm planning a large house with high ceilings and lots of windows. Is radiant floor heating practical?

High ceilings and "lots of windows" are one of the main reasons why radiant heat is chosen as a building heating system. Since hot air rises, in a forced air heating system all of the nice, usable heat is first sent to the ceiling. This may be anywhere from 10 to 20 feet up. By the time this air makes its way to your level, about 6-ft. off the ground, it has lost most of its energy and has started to get pushed down by the other hot air entering the room. If this air is cooler than when it entered, where did all of its heat go? Right out the ceiling.

Radiant heating works in just the opposite way. Since a radiant heat system stores its energy in the floor, all of the room's warmth is kept right where it needs to be, on the floor where you are. The ceiling in a radiant floor system is always much cooler than the floor area, just the way you would want it. This cooler ceiling temperature means less energy is being wasted to the outside. Less waste means higher efficiency.

Can my radiant system also melt snow and ice?

Snow melt systems are becoming more and more popular, especially in areas where nature conservation is important. Snow melt systems eliminate all of the other necessary chemicals and pollutants used today to keep areas free of ice and snow. No more salt to track indoors. No more uneven melting. Streams and rivers no longer get polluted with unnecessary additives.

Snow melt systems also protect your investment. Slabs last longer. Salt and other chemical additives will begin to break down the surface of a concrete slab over the years. For brick paver applications, snowmelt systems provide a certain amount of physical protection. Keep dangerous snow plows away and retain the beauty of your investment.

Why do we need to be heated?

Actually, we don't need to be heated, not in the same sense one might think. Since we are living beings, we actually produce our own energy, or heat, by consuming food (calories). Movements and other activities consume these calories, and a by product of this consumption is heat. Our bodies operate at around 98.6 Degrees F. By controlling the temperature of our surroundings, such as chairs, walls, windows, etc., we will have more control over our own body's heat loss, which will make us feel warmer and enhance comfort.

I've heard that older radiant heating systems made the floors too hot. True?

Yes, this is a true statement to some degree. In the past, radiant heating systems were designed and installed in much the same way as a conventional baseboard system. High temperatures and simple controls were used to control the radiant heating system. These high temperatures were in fact too high from a comfort standpoint. The higher the water temperature in the floor, the higher the floor surface temperature will become. For all systems a maximum floor temperature of 85F is maintained to ensure comfort. In these older systems, the floor temperature could actually exceed this limit, causing the floor to feel uncomfortable.

Today there are endless arrays of controls and piping methods to ensure this does not happen. Lower water temperatures are maintained to prevent over heating. Indoor/outdoor reset systems are used to help predict heating needs and to increase response times. Radiant heating technology is becoming more and more advanced everyday.

Does a radiant house take a long time to heat up from a cold start?

Most radiant floor heat systems take about a day to come up to full temperature. The reason for this is due to how the radiant heating system stores energy. Before a radiant floor can emit energy (heat) into a space, it first has to raise the floor temperature. Depending on the floor construction and the initial floor temperature, this start up time may be anywhere from a few hours to a few days. Slab on grade floors will see the largest start up time, mainly because they will have the highest mass value.

Does a radiant heating system have any impact on air circulation or cleanliness?

Yes. Since the air is not carrying the heating, and is not being forced to move through the house, less dust and mold is being distributed. This helps to keep allergies and other ailments to a minimum.

What type of floor construction should I use?

Any type of floor construction can be used with a radiant heat system. The most common will be a slab on grade, or a frame floor. Some variations of these may include a thin slab over a frame floor or a Sandwich application. The important thing to remember is to inform the radiant designer of the exact construction of the floor. There will be design variations between a frame floor project and a slab on grade. Keep in mind, it is better to design the building for what is required structurally and let the radiant system be designed around the construction details.

What type of floor coverings can be used over a radiant heat system?

Most floor coverings can be used over a hydronic heating system, keeping in mind that the system is designed for that particular covering.

Tile is the most efficient, since it is the most conductive. Hardwoods come next, and then carpet and pad. Even vinyl or linoleum can be used. Typically the only design variance between these three common floor coverings, is supply temperature.

I've heard hardwood floors should not be used. Why is that?

Hardwood floors can be used over a hydronic heating system if extra time and care is used during the installation process. Wood floors are what we call hydroscopic. That means the wood reacts to water, in much the same way a sponge does. If the wood is dry and goes into a wet environment, then the wood floor will adsorb moister and expand. Likewise, if the wood is too "wet" and is installed into a dry environment, it will dry and shrink.

Wood floors continuously move, just like the door jams in your home. In the summer they expand due to the increased humidity in the air and become harder to shut And, in the winter the humidity is typically lower, and the doors shrink, becoming easier to close.

Wood floors will also experience this seasonal change in dimensions. However, there are some "tricks to the trade" that will help minimize these swings.

  1. Use a wood that is kiln dried. This helps to ensure the wood's moisture content is the same on the inside as it is on the outside.

  2. Try to use a wood that is no wider than 3" to 3.5" in width. The narrower the strip, the less movement it can induce.

  3. A quarter-sawn wood is better than a plane-sawn wood. Plane sawn woods tend to "grow" or expand in width, while a quarter-sawn wood will tend to expand more in thickness. This helps reduce visual cracking and gapping.

  4. The wood should be around 7% - 10% in moisture content. This may require an acclimation period in order for the wood to reach this level. Sometimes, it is best to have the radiant system installed before the wood. This will help accelerate the acclimation process.

  5. The wood floor should not be higher than 4% in moisture content than the floor it is being installed onto. This will allow for the subfloor and hardwood floor to move and react as a single unit. Otherwise, moisture maybe able to travel from layer to layer.

  6. What about the nails used with a hardwood floor?

Typically, hardwood installers use one nail that will allow for the most use in the most variety of applications. However, this single nail tends to penetrate the lower surface of the subfloor, placing the radiant heat tubing in jeopardy. To eliminate this threat, ask the hardwood installers to use a shorter nail, one that will not penetrate the subfloor. And, if possible, ask them to try to keep the nails around the joists below. This way if there is some penetration, it will more likely go into the joist and not the tubing. As with any radiant heat installation it is a good idea to visually inspect the tubing after the wood floor is down, along with the factory recommended pressure test.

Is there anything in my floor that can cause problems?

In new construction there really isn't much that can is used that can cause a problem with a radiant heat system. If a vinyl floor is used, make sure the adhesive used can withstand elevated temperatures.

However, in a remodel, one thing that can be problematic is the use of tarpaper. This was used as a slip-sheet for hardwood floors to reduce squeeks and to act as a vapor barrier. Tarpaper can "off-gas" when heated up, causing an unpleasant odor to filter into the home. With today's construction techniques, rosin paper is used instead of tarpaper, which removes the off-gassing problem.

How many zones can I have with my radiant heat system?

A hydronic heating can be designed with as many or as few zones as desired. Some systems will have one zone per floor, while others will have each individual room a zone. Keep in mind the more zones there are, generally the higher the radiant heat system cost.

I'm remodeling my garage, do I have to install a boiler?

Heat sources are chosen based on the water temperatures required and the total heat load needed for the space. For most full home hydronic heating systems a boiler will be used, but in some cases, such as a single room addition, a dedicated water heater may be used. This will be based on local code allowances and other design considerations.

If a water heater is used, it is not recommended that his same unit be used to supply the domestic hot water needs. The radiant fluid needs to be isolated from the potable drinking water.

What is the best way to control my radiant heat system?

Controls are chosen mainly on how the homeowner/project owner wants their system to respond to changes in outside conditions and on operational ease. Most systems will use a type of relay control with standard thermostats. More advanced systems will use outdoor sensors to anticipate climate changes. These systems are called outdoor reset and they tend to operate more efficiently, but they do cost a bit more.

Who should I have install my radiant system?

There are professional installers in most areas of the United States and Canada that specialize in radiant systems. But, any professional building or plumbing person can install a radiant system.

Can I install part of the system myself?

It is really up to the local code to dictate whether an installer needs to be licensed. In some areas the general contractor will allow homeowners to install the tubing while they supervise the work. In most areas a licensed installer is required to install the heat source, especially if a boiler is being used. Watts Radiant recommends a professional installer be consulted or used to install the mechanical package used to control the radiant heat system.

How is heat transferred?

Heat is transferred from on location, or body, to another by three basic modes. These modes are Convection, Conduction and Radiant Heat.

One basic rule to all three modes is this: heat does not rise, hot air rises. Heat moves from a hot source to a cold source. Think of a hot air balloon. It floats because the hot air inside is less dense than the cool air outside. This literally causes the balloon to float in much the same way a boat floats on water.

Another way to think of this is to imagine a metal skillet placed on a stove burner. When the burner is turned on the handle is still cool to the touch, but as the bottom of the pan warms, the heat moves from this now warm source, to the cooler outer edges. Eventually the handle will become too hot to handle and a cooking mitten will be required to handle the skillet.

Explain the types of Heat Transfer

Convective heat transfer is what most of us are familiar with. This is how our forced air heating system or our baseboard system transfers energy (heat) to a space. Air moves over a heating element, becomes warmer and expands into the space. In a forced air environment, most of the hot air is at the ceiling, much the same way the hot air balloon rises, so will the warm air in a room heated with forced air. Convective heat transfer is the least efficient means to transfer energy.

Conductive heat transfer refers to two surfaces touching each other. Imagine a metal pan on the stove. If your hand is positioned an inch above the hot handle, you really won't feel much from the handle, and you can keep your hand there as long as you wish. But, when the handle is touched, your hand instantly begins to feel hot. This is conductive heat transfer. The pot is giving off the energy (heat) in the handle to your hand in a very fast, efficient manner. Conduction is one of the more efficient modes of heat transfer.

Radiant heat transfer is the best because it isn't slowed down by air. Radiant energy is only felt when the energy wave strikes another surface. This means the surrounding surfaces all reach set temperature. By enclosing your body by warm surfaces, we can better control how our bodies lose heat. Radiant floor heat means better comfort with higher efficiency.

What type of piping should I use?

Watts Radiant offers two different types of radiant tubing options, each has its own unique qualities. Watts Radiant's Onix tubing is the most diversified product in the market today. It is the only product that can be installed under a frame floor with no additional accessories required (no heat transfer plates, no special clips). Since the Onix does not expand or contract with temperature changes, it is the quietest system around.

Watts Radiant also offers a Pex line (cross-linked Polyethylene). This product is typically used in slab or thin-slab applications, but can also be installed under a frame floor with the use of heat transfer plates or clips.

As long as the tubing chosen is installed properly and per the manufacture's recommendations, the radiant heat system will perform beyond expectations.

Are baseboard "radiators" really radiant heat?

Baseboards are actually convectors. They heat the air by creating a temperature differential across the fins. This temperature difference "pulls" the cooler air across the heated fins. The warmed air then rises, adding to the pull.

Radiators operate in a similar fashion as a baseboard unit, but with one difference. Because radiators have a much higher mass and tend to have more exposed heated surface, they do provide a certain amount of radiant heat to a space.