In Grand Rapids, Michigan, Andy Zbojniewicz is planning a large, high-performance home that ultimately will be powered by a 15-kW solar array. The house will have more than 3,000 square feet above grade, and another 1,633 square feet in the basement.
His immediate concern is how to heat and cool the house.
“I was told the home was too large to heat and cool with air-source heat pumps and be comfortable,” Zbojniewicz writes in a Q&A post, “so [I] was primarily looking at geothermal.”
To that end, Zbojniewicz sought quotes from two HVAC contractors for ground-source heat pumps. One of the contractors said the heating load would be 50,797 Btu per hour at an outside temperature (design temperature) of 7°F, and recommended a 5-ton (60,000 Btu/h) heat pump. The second company didn’t provide its load calculations, but suggested that Zbojniewicz would need two 3-ton heat pumps in order to stay comfortable.
“I have a friend who is in HVAC and he feels strongly that I should have radiant tubing run in the basement to help with heating in winter,” Zbojniewicz adds, “and while I was at it I was going to run it in the mudroom, master bath, and three-season porch.”
After doing some reading at GBA, Zbojniewicz realizes there are plenty of critics of both ground-source heat pumps and radiant-floor distribution systems.
“Is there a better alternative to geothermal if I want to have the potential for net zero?” he asks. “If I stick with geothermal, are two 3- ton heat pumps overkill (they’re certainly more expensive)? Should I abort the radiant altogether?”
That’s the topic for this Q&A Spotlight.
There is nothing wrong with air-source heat pumps
The outside design temperature for Grand Rapids, Michigan, is 5° or 6°F, GBA Editor Martin Holladay says,…
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