Refrigerant Line Set Insulation on an AC or Mini-Split: What the Code Requires
Insulate the vapor (suction) line. On a heat pump it needs at least 0.75 inch of insulation or R-6.0 in a home, and the liquid line needs none. Outdoors the insulation needs a weather cover that is not adhesive tape, and suction lines outside conditioned space need a sealed vapor retarder.
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Which of the two lines
Section 150.0(j)1B sends space-conditioning piping to Section 120.3(a), which covers refrigerant suction lines in cooling. A heat pump's vapor line is the suction line in cooling mode. For a heat pump in a residential building the vapor line takes at least 0.75 inch of insulation or R-6.0, and no insulation is required on the liquid line (Exception to Section 120.3(a)2). Factory-installed piping within certified equipment is excepted (Exception 1 to Section 150.0(j)1).
The thickness to specify
For cooling-only suction lines, Table 120.3-A-2 sets 0.75 inch for residential pipe under 1.5 inches nominal diameter, and 1.0 inch for larger pipe. Residential line sets are normally well under 1.5 inches, so 0.75 inch is the number to put in the order.
Outdoor runs and cold spots
- Insulation exposed to weather needs a cover suitable for outdoor service that is water retardant and shields it from sunlight. Adhesive tape does not count as that protection (Section 120.3(b)1).
- Suction piping outside the conditioned space needs a Class I or Class II vapor retarder in or over the insulation, with every joint and penetration sealed (Section 120.3(b)2).
- Insulation buried below grade must sit in a waterproof, non-crushable casing or sleeve (Section 120.3(b)3).
Where insulation can be left off
Piping through framing members needs none for the thickness of the framing, though metal framing needs grommets or wrapping so the pipe never touches it. Piping surrounded by 1 inch of wall insulation, 2 inches in a crawlspace or 4 inches in an attic is also excepted (Exceptions 2 and 4 to Section 150.0(j)1).
What this page does not cover
The building department decides what it inspects and when. This page covers the energy rules only, and manufacturers may call for more, so follow their instructions as well.
Related pages: the mini-split checklist, duct insulation, charge verification and installing a mini-split yourself. Reports for these jobs start on the residential page.
Common Title 24 Questions
- When is Title 24 required for a home?
- Does a remodel need Title 24?
- Does a room addition need Title 24?
- What plans are needed for a residential Title 24 report?
- How much does a residential Title 24 report cost?
- How long does a residential Title 24 report take?
Frequently Asked Questions
No. For a heat pump the code requires insulation on the vapor line only. The liquid line needs none, although manufacturers may still ask for it.
No. The code requires a cover suitable for outdoor service that is water retardant and blocks solar radiation, and it says adhesive tape shall not be used to provide that protection.
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- Installing a Mini-Split Yourself: What Title 24 Still Requires
View all Mini-Splits guides → · HVAC and Water Heating · Title 24 guide