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Case Study: Full Retrofit

Before the Assessment:

Furnace and AC retrofit projectThis one-story, 1,900-square-foot house on slab concrete foundation had never been remodeled and had all of its original features: steel-casement windows, large sliding glass doors, original furnace, and in-floor ducts and vents.

The Retrofit:

Low attic insulation; a leaky building envelope; a wasteful furnace, old A/C and duct system; no air sealing at the skylights; and electrical/plumbing penetrations that were allowing hot/cold air into the building envelope.

What was done: 

The existing furnace, A/C and ducts were replaced with a hydronic furnace, 14 SEER A/C and R-8 ducts in the attic. The attic was air sealed, and attic insulation was increased to R-38. Insulation was added to the exterior walls to achieve R-13.


Before Retrofit

After Retrofit

Duct Leakage

334 CFM25

19 CFM25

Air Leakage

2222 CFM50

1861 CFM50

AC Size

5 Tons

2 Tons

Furnace Size

100,000 BTUs

36,000 BTUs

Attic Insulation



Wall Insulation



Duct Insulation






Homeowner's Comments:

"I'm thrilled with the retrofit. I learned so much about what it takes to make and keep a house comfortable. My metaphor for the retrofit was that it was like taking an outfit to the tailor and coming back with a garment that suddenly looks and feels ten times better than it did before. Installing a hydronic unit instead of a traditional forced-air gas furnace was my biggest decision. Then I decided to place the new hydronic furnace in the attic and not attempt to reuse the floor ducts because the ducts could not be tested for static pressure. It was clear, though, that the old ducts would not be able to deliver the optimal air flow and air mixing to the rooms that the smaller A/C and hydronic heater needed to provide efficiency and comfort. The hydronic unit is in the center of the house to keep the duct runs as short and direct as possible. It is so quiet that you cannot tell the heater is on unless you put your hand up to a vent. And the smaller A/C is much quieter than the old one."

"The wall insulation also makes the house much quieter inside. It's interesting to note that during the retrofit, air sealing was necessary around the skylights and plumbing fixtures but the windows and doors were left untouched. When the Energy Upgrade California inspectors came by and re-audited the house to verify the retrofit results, they told me the house was so airtight that if I had not added continuous-use exhaust fans to the bathrooms they would have required me to do so, to make sure enough fresh air was being drawn into the house. I guess I was just surprised to find that my original windows and doors performed so well."