Domestic Hot Water Recirculation Part 6: Maintaining Temperature Control In Systems with Steam Instantaneous Water Heaters

Applying recirculation to domestic hot water systems with steam type instantaneous water heaters requires a little extra attention. The challenge is temperature control. Under very low load conditions, instantaneous water heater supply temperatures may fluctuate rapidly – even dangerously. Here’s why: During periods of light draw, the heater flow rate may become unstable, fluctuating between a minimal/no load draw recirculation flow rate and that same flow rate plus the draw of a single fixture. That’s what happens when a single hotel guest decides to take a shower at 3AM.
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