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Ideas for resolving one hydroair zone freezing
I am a homeowner with a Buderis gas boiler that supplies hot water to 6 radiant zones, 4 hydroair handlers, and the hot water tank. All of the zones and air handlers are within conditioned space with the exception of one hydroair zone that supplies one wing of the house over the garage.
The air handler for this one zone that intermittently gives us trouble is in an insulated, but unconditioned attic. The hydroair tubing goes up through an outside wall to this attic, although the outside wall has foam insulation. It then traverses a short section of the sloped roof before entering the attic where the air handler is located. I suspect the traverse through the roof is the section most exposed to the outside cold temperatures.
This one zone freezes up on the frigid cold days of winter and we lose heat to that section of the house. We have added antifreeze to the system, twice over the last 4 years, at a cost of thousands of dollars each time. Most recently, after adding the antifreeze, we got through one heating season with no freezing. Then last winter the system tested to no freezing down to zero, but during a very cold snap, that zone again froze for a few days until the outside temperatures rose. We are currently awaiting our appointment for system maintenance and performance check, including a freezing point depression check to be ready for the winter.
I am getting frustrated with the episodic freezing up of this one zone. I am wondering if there might be a more permanent solution. First, I am tired of adding thousands of dollars worth of antifreeze to the system every two to three years, the antifreeze cost is as much as my energy cost for a whole heating season in my otherwise highly insulated home. Second, we want to have a system with a higher degree of reliability and trouble free performance.
Is there some type of recirculator we could add to this one zone, triggered only by very low outside temperatures, that would keep this zone from freezing? I am also looking for any other thoughts regarding this situation.