By Hilary Jenkins-Spangler
My husband and I recently finished building an energy efficient, earth-bermed house in Fallston, Maryland. We chose a ductless mini-split system to heat and cool the home.
We live in a mixed humid climate, where temperatures often reach below freezing in the winter and the upper 90’s in the summer. Although our winters can be quite cold, we are classified as having a Zone 4 subtropical climate. I knew we needed an efficient and effective HVAC system to deal with the wide range of temperatures and humidity we experience in Maryland.
I even took a weeklong course on building science before I made my final decision. There, among other things, I learned the importance of right-sizing an HVAC system. To make sure we got this right I had an engineer friend calculate the specific heating and cooling requirement for our tightly insulated home.
Although most homes with an interior conditioned space of 2000 sq. ft. in our climate would require more, we found we needed just under 18,000 BTUs. This is largely due to the fact that our home is below grade and earth-bermed. We considered geothermal heating and cooling but decided to look for other options after one geothermal installer quoted us $50,000 for that type of system. I had heard about ductless mini-split air conditioning and heat pump systems from a Passive House Consultant/Architect and after doing some additional research myself, it seemed like a good fit for our project. This approach was far less costly than geothermal, but had the potential to save us just as much (if not more) energy. So that’s what we chose.
What ARE Ductless Mini-splits?
Ductless mini-split systems differ from more conventional systems because they eliminate the need for an indoor evaporator or bulky ductwork. Instead, refrigerant is cycled through the lines from the outdoor compressor/condenser unit to the indoor wall and/or ceiling mounted unit(s), which quietly distribute the conditioned air to the interior space.
We installed two, 9,000 BTU cassette/ceiling mounted units – one on each level of our home at a cost of around $4,000. (Note: I am a general contractor so I ordered and hung the units myself and my HVAC contractor hooked them up. The costs would be higher for a typical homeowner.) The units are connected to an outside compressor/condenser unit via a line set so no ductwork is involved, just 3” holes in the wall. Due to the fairly open nature of our floor plan we only needed two interior units. We also have radiant floor heat in the bathrooms and master bedroom and a pellet stove for back-up heat.
Yes—I’m Happy With My Decision To Use Ductless Mini-splits
Installation was quick and easy – it took about a day. Our units heat, cool and dehumidify with amazing efficiency and each one has its own thermostat. Our summer electrical usage in July peaked at 800 kWh ($120 @ 15 cents per kWh). Temperatures were in the upper 90s and humidity in the 80s but our house remained comfortably cool. Our bills were a little higher this past winter, but there were other factors that impacted the higher cost.
Needless to say we are delighted with the mini-splits. Not only is the system efficient, the indoor units are so quiet the only way we know they are on is by looking at the green light on the cover! They are a fraction of the cost of geothermal and quite possibly more efficient. As contractors become more familiar with the technology and more consumers learn that this is an option, I’m sure we’ll see many more mini-splits going into homes.
Hilary Jenkins-Spangler lives in Fallston, MD with her husband and two young sons. She is a consultant/general contractor/designer for energy efficient, environmentally friendly homes. She studied Interior Design/Architecture at the University of Maryland and also worked for 7 years as a furniture maker. You can read more information about the construction of her energy efficient home on my blog: blog.jenspan.com