This approach utilizes a dedicated heat source for the radiant floor. The fluid in a closed system is re-circulated around and around in a completely closed loop. There is no connection whatsoever to the domestic water supply. The main advantage to this system lies in the fact that, being closed, anti-freeze instead of water can be used as the heat transfer medium. Closed systems are often used in second homes or primary residences in areas prone to long power outages. If freeze protection is an issue, than a closed system with anti-freeze is a good idea.
The down side is two heat sources. All water heaters waste heat energy, even when the burner is off and the unit is sitting idle between heating cycles. Granted, the unit dedicated to heating the floor only wastes heat during the winter months. But standby losses for six months out of every year can add up. The other consideration is efficiency. Two low or moderately efficient water heaters are much more costly to run than one high-efficiency unit.
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A beautifully installed six zone closed system using a Polaris high efficiency water heater |
If you are using a boiler for a heat source, a mixing valve is required. See below.
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If you have a single zone system, your plumbing schematic will look like this:
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| The photo on the left is our "Radiant Ready" single zone Closed System package. This pre-assembled, panel system comes right out of the box just as you see it here, including pump, pre-wired controller, expansion tank, air eliminator, in-line thermometers, and various gauges and valves. The entire package is pressure tested against leaks and as few as four solder connections can tie it into your system. | |
This customer chose to use Unistrut channel to mount his "Closed" Radiant Ready package instead of the plywood board included in the kit, but the result is the same -- a clean, compact, beautiful do-it-yourself installation. Note the addition of a mixing valve (the silver, three-way valve with the gray knob) to this system. This gives the customer a more precise control of the system's water temperature.
Radiant floors, one or several zones, are often added to existing hot water baseboard or cast iron radiator systems. To install a "hybrid", part radiant floor, part baseboard system, follow this schematic:
Radiant Floor Company can customize a Zone Manifold to suit any application. In this case, one leg on the left side of the manifold feeds a baseboard zone with straight 180 degree boiler water. The two legs to the right of the mixing valve supply the radiant tubing with boiler water that has been tempered by the return water down to 125 degrees.
A single radiant zone coming off an existing boiler.
The hose on the right is filling the newly installed radiant tubing with water. The hose on the left runs to a drain and purges the air from the system. Once the system is charged, the hoses are removed and the valve between them is opened. This same line is the hot supply from the boiler. It enters the hot side of the mixing valve. The "cold" side of the mixing valve is supplied by taking a branch from the floor's return line just before it reaches the boiler. That way, the heat lost to the floor is reclaimed by bleeding small amounts of super hot boiler water back into the return water. The mix of the two goes to the pump and back to the radiant floor.
Using an Outdoor Wood Boiler With an Closed System
Many customers, especially in rural areas, are installing outdoor wood boilers and using them in conjunction with radiant floor heating. Normally, these boilers, via a heat exchanger, are plumbed into a storage/back-up tank that can take over the task of heating the water when the winter fatigued homeowner flies off to the Caribbean and becomes unavailable to throw wood into the boiler.
If you have an outdoor wood boiler, and for whatever reason you need to use antifreeze in the radiant floor system, the following schematic should be very helpful.
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Outdoor wood boiler with separate storage/back-up tank
Some outdoor wood boilers are either multi-fuel systems (i.e. they can burn wood and gas or oil) or they have a built-in heat exchanger coil to supply domestic hot water. With this style of boiler the separate storage/back-up tank is not needed and the radiant floor can be run directly from the boiler.
The following schematic applies to the above mentioned types of outdoor wood boilers. Just remember to bury the supply and return lines from your boiler below the frost line. Here's why...
Normally, the wood boiler is plumbed to a heat exchanger (see drawing above). As you can see, this allows the boiler to heat a tank of potable water, which in turn can provide domestic hot water AND floor heating (in an "open" or "closed" configuration).
The water from the boiler to this heat exchanger flows 24 hours a day in a closed loop, making the heat exchanger "continuously active" (i.e. always hot). Whenever needed, the storage tank draws heat from the heat exchanger and maintains a constant tank temperature. The advantages of a continuously active heat exchanger loop are twofold:
1) the pipe from the wood boiler to the house can be buried in a shallow trench (normally about 1 ft.), saving a lot of labor and/or expensive excavation costs (obviously, with constantly circulating hot water in the supply and return lines, freezing is impossible, even in a trench well above the frost line), and
2) by keeping the water in the boiler constantly circulating, stratification is eliminated. In other words, without constant flow through the boiler, the water at the top of the water jacket gets VERY hot, and the water at the bottom stays much cooler. And since most boilers have water jackets containing several hundred gallons of water, 50% of the water in the boiler could be 185 degrees (the temperature at which the boiler damper shuts off the air supply and sends the boiler into resting mode) and the other 50% could be considerably cooler.
This means, in essence, that a boiler sized to provide X number of BTU's of heating capacity is now providing considerably less than it's design rating. Because when one of the heating zones calls for heat, a circulator pump comes on, water again flows through the boiler stirring the hotter and cooler water together, and suddenly 185 degree water becomes 145 degree water. This can really matter in a marginally sized system.
So, the point is, if you want to run a radiant system directly off your wood boiler, always bury your supply and return pipes below the frost line. As explained above, the water to and from your house will only be flowing when a radiant zone calls for heat. And because many outdoor wood boilers are 30 to 100 feet away from the home, a lot of water can be sitting in a cold (though admittedly insulated) trench for a long time. If that trench is above the frost line, you could have serious trouble.
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Multi-fuel wood boiler, or boiler with built-in heat exchanger for domestic hot water. The lines to and from the boiler must be buried below the frost line.
Connecting the EPK to the Zone Manifold
The following drawing outlines the copper fittings necessary to connect various sizes of Expansion and Purge Kits to the Zone Manifold. These fittings and a hard copy of this drawing are included with every Closed and Heat Exchanger system.
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