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Kick Heater not compatible with high-efficiency boiler?
We are replacing a 25-year old cast-iron boiler + standard 50 gallon direct-fired hot water tank (rated 40 gal/hr recovery). Goal is more hot water (3 girls who like to take long showers, and we seem to run low on hot water after the first shower), quick recovery, and trouble-free heat. Got a quote for a Weil-Mclain GV90+4 + WM Indirect 40 gallon (might go to a ~55 gallon to get more hot water). Second quote was a Viessman B2HA-35 + Vitocell 53 or 79 gallon Indirect. Viessman is about 50% more expensive, but is more efficient (95% vs 90%?). However, we have a kick heater in the kitchen and the Viessman guy said that this might be a problem with the high-efficiency boiler, i.e. the system would have to run much hotter to turn on the kick heater, so this negates the benefit of the high-efficiency boiler. He said we should go back to baseboard but that's not an option.
Does this make sense? I think that the kick heater needs ~120 degree water to turn on. From a similar model: "For consistent response of the reverse acting thermostat, and effective outlet air temperature,
the average water temperature should not be below 120° F (49° C). Blower motor shuts off at
105° F (41° C) and will not operate until water temperature reaches 120° F (49° C)."
Will we have problems with the kick heater?
Any opinions on whether the Viessman is worth the much higher cost? Seems like it would take 10+ years to make up the extra cost.
Reliability: Viessman has a reputation as a higher-quality unit, but many people are telling me that ANY high-efficiency unit will be LESS reliable than a more conventional cast-iron design like the Weil-McLain.
Thanks in advance for any advice!