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The Best Systems

No one radiant heating system is ideal for all situations, but after 30 years of serving customers, a few systems and techniques stand out.

We like simple honest value, with no gimmicks or do-dads. Systems should be reliable, long lasting, and easy to work on. They should be energy efficient and environmentally responsible and they must be affordable. The best radiant heating systems should offer the features at right.

Check out our video below to learn more about the best radiant heating system.

The Best Systems Should Offer:

  • Low initial cost
  • Low operating cost
  • Environmental sensitivity
  • Energy efficiency
  • Simple and easy to work on
  • Compatibility with solar energy
  • Should be “DIY friendly”

The Best Overall Heating System

Open Direct System Schematic

Simplified Schematic of The Open Direct System

In light of the above, the best systems will use a high quality, high efficiency hot water heater instead of a boiler. These systems cost about half as much as one using a typical boiler system and yet are much more efficient. They are a simple, ingenious way to make radiant space heat, domestic hot water and even pick up some free cooling, all within the same unit. If you use a boiler, you will incur extra costs and miss out on some great opportunities.

Domestic hot water based heating systems are so affordable, they make the exceptional comfort, high efficiency, and health benefits of a radiant heating system available to everyone – not just the one percent!

Open Direct System

Photograph of the Open Direct System

You can use the same water heater for your radiant heating system that you use for domestic hot water!

There are two systems to choose from that use the domestic water heater as the energy source for your radiant heating system, the indirect system that uses a heat exchanger and the direct system that does not.

Click here for more information about radiant systems that use the domestic hot water heater as the heat source.

The Direct System

(shown here in heating mode operation, one of three possible modes)
Click here for detailed information

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Open Direct Legend

These radiant heating systems are arguably the
best and most efficient heating systems available.

Heating systems that are based upon the domestic water heater cost about half as much as one using a typical boiler system and yet are much more efficient. They are generally made of better materials. They are a simple, ingenious way to make radiant space heat, domestic hot water and even to pick up some free cooling, all within the same unit. Properly designed domestic hot water based systems meet all major codes and are exceptionally safe. Because these systems operate at low temperature they are more energy efficient and safer than systems using a boiler. The expense of a boiler is also entirely eliminated, making these sytems more affordable as well. Domestic hot water heater based heating systems are even compatible with a solar energy assist.

These systems are sometimes labeled “controversial” by people in the heating industry that want to sell you an old-school boiler system that costs 2 to 3 times as much. We have the science and happy customer feedback to back up our systems. It is up to you to consider the source of any negative comments.

The Best Heating Unit


The Polaris Water Heater.
Note the giant stainless steel
exhaust flue for extra efficiency.

The Polaris heating unit is a water heater (not a boiler) that is engineered to make space heat as well as domestic hot water. Because it is engineered to make warm water instead of boiling hot water right from the beginning, it is incredibly energy efficient – and safer as well. The Polaris is all stainless steel. A huge submerged stainless steel flue extracts just about every possible BTU of heat from the flue gas. Standby losses are nearly eliminated.

Even with these benefits, the polaris costs far less than a similar capacity boiler. It’s a good value to buy, and a good value to continue to operate over time.

Click here for more information about the Polaris.

The Best Heat Exchanger Tubing

The least desirable place to cut cost is with tubing and fittings. Heat exchanger tubing often goes into inaccessible places where it would be difficult to replace. Is the material approved? Can you work with it? Is it energy efficient? Do not use waterline that has been retasked as radiant heating pipe. It is not worth it.

Here are some of the benefits to proper tubing selection:

Tubing of various sizes made of various materials

  • Higher heat output
  • Less pumping cost
  • Longer circuits possible
  • Lower, safer operating temperatures
  • More energy efficient
  • Longer service life
  • Lower electric bills
  • Quieter operation
  • Compatibility with solar heating and alternative energy.

Click here to learn more about high efficiency radiant heating tubes.

The Best Detail for a Joisted Floor

View of a Joisted Floor System 'Staple-Up'

Photograph of a Joisted Floor System “Staple-Up”

Many commonly offered systems on the market do not work very well, or cost too much. The following details are very important for performance and cost.

We recommend you heat the floor with tubing installed in the joist spaces beneath the sub floor. Use 5/8″ PEX with .070 wall thickness. Use high efficiency tubing. Space the tubing 8″ apart within a 16″ joist space. Use thinner gauge aluminum heat emission plates and use them everywhere if possible.

The 5/8″ tubing is larger than typical 1/2″ material. It puts out more heat and allows the system to operate with lower fluid temperatures for longer life and better efficiency. The larger size reduces pump work and allows longer circuits. Tubings which are larger than 5/8″ may be too difficult to work with.

The aluminum plate takes heat away from the tubing and distributes it throughout the sub floor. Research shows that this detail is very important. The plates support the tubing well and the improved heat transfer is significant. Thinner aluminum plates have equivalent performance as thicker plates with half the cost.

Thermograph without aluminum heat plates

Comparison of radiant tubing effect with and without aluminum heat plates.

The aluminum material has a very important and often overlooked property. Aluminum radiates much less heat into the air than other materials. This property sharply reduces heat loss in the downward direction (back loss) and has the effect of insulation. It is very important to control heat loss in the wrong direction as these losses can nullify most of the benefits of radiant heat.

Click here to read our research report about aluminum heat emissions and heating performance.

The radiant thermograph on the right shows a significant difference in floor temperature when aluminum plates are used. The far (orange/yellow) side of the floor has aluminum plates, the rest of the floor has radiant tubing but no heat plates. You can see from the legend in the right of the photo that this represents a significant difference in temperature.

Thermograph of operating aluminum plates

Thermograph of operating aluminum plates

The radiant thermograph (right) shows that the aluminum plates (blue) emit much less heat than the surrounding areas (red, orange) even though they are at a much higher temperature. This property means that the plates are taking the heat away from the tubing, distributing it throughout the floor, and then, making the heat go in the right direction.

Feel free to contact customer service technicians if you would like more information about these details. Customers may also request a research report.

The Best Details for Slab on Grade Construction

Insulation Details

Slab on Grade

Schematic showing Slab on Grade

Our experience and research indicates that under slab insulation is most important at the perimeter and less important in the center of the building. Insulation should be extruded polystyrene. We know of no other acceptable material. In cold climates, it should be 2 inches thick at the perimeter and may taper off to 1 inch as it goes inward towards the center of the building. Insulation should extend 12 feet from the perimeter towards the center in cold climates but can be reduced to 6 feet in warmer climates. Our experience indicates that failure to insulate properly is one of the most serious mistake that you can make.

Concrete reinforcement

“Rod” type reinforcement is preferred over the “mesh” type because of overall strength and workability. Put down half of the reinforcing first and set it on “chairs” or bricks. Then lay out the tubing. Lay out the other half of the reinforcing on top of the tubing and tie everything together. It will be easier to lay out the tubing (because only half of the tubing is placed), and the tubing will be well protected by the reinforcing. The reinforcing will carry heat away from the tubing, and the reinforcing is generally well placed with half above the centerline of the slab and the other half placed a little beneath. Fiberglass reinforcing fibers are not a substitute for steel reinforcing.

Tubing Size and Spacing

If the slab is to be of any significant size, (500 square ft or larger), a larger diameter tubing is preferred (up to 7/8″ diameter). A larger tube (within reason) will put out more heat, reduce pump work and enable longer circuit lengths. Tube spacing may be spaced 24″ on center in very efficient and stable environments (such as basements). A 16″ spacing is more typical for reasonably efficient residential construction and 12″ spacing will provide a little more heat and a more rapid response time.

Tubing Spiral

Tubing layout should be a spiral or have gentle turns by another design.

Detailed research (DOE) has shown that 7/8″ PEX tubing with 0.70″ wall thickness and a circuit length of 200 feet is about ideal. The electrical energy consumption of the pumps will be as low as possible and the flow will be just slightly turbulent. The temperature drop will be about 10 degrees F from inlet to outlet. This is ideal, but different designs can still produce satisfactory results.

Tubing layout should be a spiral or have gentle turns by another design. Very tight turns strain the material and raise pumping costs. There is no benefit to a very tight and very evenly spaced design.

Click here to learn more about the benefits of an engineered tubing.

The Best Solar Heating System

If you start out with a domestic hot water based heating system it is easy to add a solar supplement; either now or in the future. Solar domestic water heaters are well proven and accepted.

The “Solar Option Two” heating system is an extension of successful solar domestic hot water applications. In the right place, the solar domestic water heaters have been successful as long as the work is done right and the domestic hot water production is valued (schools and churches are often not appropriate, residential construction is often ideal).

The radiant heating system is designed to use the domestic water heater as the energy source and additional solar panels are provided so that some contribution to space heating or other energy needs can be made. The overall system may be limited by the ability of the house and system to store heat.

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This system, either as a solar “assist” or in a building that already has its own “thermal mass” is cost effective in all areas of the Continental United States when it is planned thoughtfully.

Click here to visit our solar heating website

The Best Pumping Design

Radiantec's Zone Distribution Manifold
Every month of the heating season, you must pay the electric company for the energy that your pumps use. It is most efficient to use a single individual pump for each heating zone.

The alternative would be to use one large pump and individual zone control valves. This is a common practice, but it is not good design. The pump must be sized so it is large enough to provide adequate flow when all of the zones are calling for heat but most of the time, only one or two heating zones are calling. The pump is too large for the task resulting in a waste of electricity and unnecessary wear and strain on the system.

A zone valve costs nearly as much as a small pump so there is really no money to be saved by using them. Small pumps are mass produced and cost much less than larger pumps.

Radiantec provides adjustable three speed pumps that can be set to meet your needs with the lowest amount of electrical use possible.