Recently there has been confusion on interpreting the insulation requirements for refrigerant lines connecting the indoor and outdoor units of heat pumps. The following are SDCI’s requirements for insulating refrigerant lines and how they differ between residential buildings and commercial buildings.
”Residential buildings” include single-family and two-family houses, townhouses, and multi-family buildings of three stories or less.
There is a conflict between the two applicable code sections copied below. Where there is a conflict between a general requirement and a specific requirement, the specific requirement governs. See Seattle Residential Code (SRC) Section 101.5 and Seattle Energy Code (SEC) Section R101.4.
The insulation of refrigerant piping requirement per SRC M1411.6 is the more specific requirement and governs over the requirements of SEC R403.4. SDCI enforces the SRC M1411.6 minimum requirement of R-4 insulation on the vapor lines. Insulate liquid lines as required by the system manufacturer. (Mini-split and split system heat pumps typically require liquid line insulation.)
- SEC R403.4 Mechanical system piping insulation. Mechanical system piping capable of carrying fluids above 105°F (41°C) or below 55°F (13°C) shall be insulated to a minimum of R-6.
Exception: Up to 200 feet of hydronic system piping installed within the conditioned space may be insulated with a minimum of ½-inch insulation with a k value of 0.28.
- SRC M1411.6 Insulation of refrigerant piping. Piping and fittings for refrigerant vapor (suction) lines shall be insulated with insulation having a thermal resistivity of not less than R-4 and having external surface permeance not exceeding 0.05 perm [2.87 ng/(s · m2 · Pa)] when tested in accordance with ASTM E96.
“Commercial buildings” include all buildings not defined as “residential buildings,” and include multi-family buildings four stories or taller plus all other buildings. The following minimum insulation is required:
- 1″ insulation on the outdoor portion of the suction line
- 1/2″ insulation on the indoor portion of the suction line
- 1/2″ insulation on the liquid line for split systems, mini-splits, and others where insulation is required by the manufacturer.
- No insulation required on the liquid line for other heat pump types.
(Seattle Energy Code amendment) C403.10.4 Insulation of refrigerant piping. Refrigerant piping, other than piping factory installed in HVAC equipment, shall have minimum 1/2-inch insulation within conditioned spaces and 1-inch insulation outside of conditioned spaces, at a conductivity rating of 0.21 to 0.26 Btu x in/(h x ft2 x °F) with a mean temperature rating of 75°F.