Dual purpose hot water tanks on radiant floor heating systems. 

Is there a dual purpose hot water tank heating your residential radiant slab. Perhaps an Apollo Hydroswirl water heater? Need to replace an Apollo water heater?  About ten or fifteen years or so, a common practice here in the Calgary area was the use of the Apollo Hydroswirl Dual Purpose Hot Water Heater. This hot water heater had side hearing outlets available to supply hot water from the tank to such things as fan coil units (air handlers) or radiant slab heat. Most commonly used for radiant slab applications, the drawback of course was that the hot water that was drawn from the tank through the space heatin

radiant floor was the same water one showered or bathed in. Unless the space heating equipment and components were non-ferrous (ie copper, stainless or bronze) they were subjected to corrosion, even if galvanized fittings were used. This led to discoloration of the hot water supply and was very noticeable in the bath water. Another problem occurred during the warm months when there is no heat demand and no flow through the space heating equipment or radiant slab tubing. This led to the water becoming stagnant, which can cause bacteria to grow and flourish. Once the heating demand was renewed and this stagnant water once again flowed through the system, this bacteria was then allowed to mix into the domestic hot water supply.

Attempts were made to incorporate pump timers so that the pumps came on every day or two to keep the water in the space heating side from stagnating. But lack of proper maintenance and lack of system knowledge with most homeowners led to the timer being incorrectly programmed or malfunctioning.

We have run across a host of these Apollo dual purpose hot water tanks failing around about the 11 to 15 year stage. When these units fail, we then separate the space heating side from the domestic hot water side using either an external heat exchanger or a hot water tank such as the Bradford White Combi2. The Combi2 has an internal coil heat exchanger which allows for effective isolation of the domestic hot water from the water used on the space heating side, eliminating the water stagnation problems of the past.

The same isolation can be achieved with the use of an external brazed plate heat exchanger option such as the Taco XPB. There are numerous options available for each situation, please contact us to discuss the best solution for your application and budget. In this kind of application we would use the Bradford White GX-1-55 high performance hot water heater to replace the actual Hydroswirl hot water heater.

We strongly suggest, that if you have one of these Apollo Hydroswirl Dual Purpose tanks in your house supplying both your domestic hot water and space heating, look into getting it replaced soon. Especially if it is in the range of eleven to fifteen years old. This is for two reasons, the property damage potential should it begin to leak but also for the sanitary reason. You would not want to bathe your newborn or young children in water that might have been sitting stagnant for a few months. Food for thought!



The panel shown above was commonly used to distribute water from a dual purpose nor water tank. These panels used potable water from dual purpose hot water heaters such as the Apollo Hydroswirl. Today potable water circulating through radiant floor systems are no longer acceptable for a number of reasons. Most notably is the risk of bacteria caused from water stagnation during the summer months.
For true separation of potable and non potable water while using a dual purpose hot water heater, Taco has come up with the ultimate control. The Taco X Pump block, shown above, is a quick efficient answer for Emco radiant panel replacements.

replacement for emco radiant panel tekmar control

Contact us at: info@generalplumbing.ca

Alberta General Plumbing

Or phone: 403-390-1115

9 thoughts on “Dual purpose hot water tanks on radiant floor heating systems. 

  1. What do you suggest for a replacement unit and what is the cost of switching? I have been told the Bradford- White unit is a good option. Does anything need to be changed on the control board when changing the heater? Thanks, Tom

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