Minisplit operating advice
We are in the first Vermont winter with out Misubishi heat pumps. Having experienced less efficiency and poorer heating performance than expected, the installation contractor provided a follow-up visit. We had been turning the thermostat down by several degrees overnight to reduce electricity use. However, the contractor advised that we should leave the thermostat set at the same temp as during the daytime to maximize efficiency. They indicated that more electricity is required for the unit to recover to the desired daytime temp than would be saved by lowering the thermostat overnight. However, I’ve more recently seen advice from Mitsubishi that the set point should be reduced 4-6 degrees overnight to maximize efficiency. We’d like to resolve this conflicting advice.
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Replies
Buckhill,
Your contractor is right. A ductless minisplit operates best without nighttime setbacks.
Here is what I wrote on the topic in 2015:
"Turning your ductless minisplit on and off, or controlling it with a setback timer, will result in higher rather than lower energy bills. These units are designed to modulate, and operate at higher efficiencies when they run continuously than when they are turned off and on."
Here is a link to the article: "Rules of Thumb for Ductless Minisplits."
Mitsubishi's advice has it wrong, more wrong in a VT climate than in milder climates, but still wrong.
"Set and forget" works best, even better if using one of the wall thermostat options than relying on the intake-air temperature sensor inside the unit to determine the modulation level.