How to Insulate Pipes
Updated February 20, 2026
Wrap exposed pipes with foam insulation to prevent freezing, reduce heat loss, and stop condensation sweating. Under $20 in materials for most homes.
Overview
Pipe insulation does three things: prevents freezing in cold weather, reduces heat loss on hot water lines (saving energy and getting hotter water to fixtures faster), and stops condensation on cold water pipes in humid environments. Foam pipe insulation costs $1-3 per 6-foot section and installs in seconds -- slit it open and snap it around the pipe. Focus on pipes in unheated spaces first: crawl spaces, attics, garages, exterior walls. The first 6 feet of hot and cold pipe leaving the water heater are the highest priority.
What You'll Need
Safety First
- Wear gloves and eye protection when working in crawl spaces or attics. Insulation fibers, dust, and sharp objects are common.
- If insulating near a gas water heater flue pipe, keep foam insulation at least 6 inches away from the flue. Use fiberglass wrap with foil backing for any pipe within 6 inches of the flue.
Step-by-Step Instructions
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Identify Priority Pipes
Walk the house and identify exposed pipes in unheated spaces: crawl space, basement, attic, garage, exterior walls. Hot water pipes lose heat. Cold water pipes freeze. Both benefit from insulation. The first 6 feet of pipe leaving the water heater (both hot and cold) are the single highest priority -- this is where the most heat loss occurs.
Tip: Pipes inside heated living spaces generally do not need insulation. Focus your effort and budget on unheated areas. -
Measure Pipe Diameter
Foam insulation comes sized to specific pipe diameters. Most residential supply lines are 1/2 inch or 3/4 inch. Measure the outside diameter of the pipe (or bring a sample to the store). The insulation packaging lists the pipe size it fits. Buy enough to cover all priority pipes plus 10% extra for cuts and waste.
Tip: 3/4 inch is the most common residential size for main runs. 1/2 inch is typical for branch lines to individual fixtures. If in doubt, 3/4 inch insulation will work on 1/2 inch pipe -- it just fits loosely. -
Cut and Install Foam Sleeves
Pre-slit foam insulation: open the slit and snap it around the pipe. Push the slit edges together. For un-slit tubes, use a utility knife to cut a lengthwise slit. At elbows and tees, cut the foam at 45-degree angles to miter the corners. Push pieces tightly together with no gaps.
Tip: Gaps are where pipes freeze. Every joint, elbow, and tee needs coverage. A 1-inch gap in insulation is where the pipe will burst. -
Secure the Insulation
Tape every seam and joint with foil tape or insulation tape (not duct tape -- it degrades). Tape the lengthwise slit closed every 12-18 inches. Tape where sections butt together. Tape mitered corners. The insulation should be continuous with no exposed pipe visible.
Tip: Cable ties or zip ties work as backup to hold insulation on overhead pipes where tape alone may not hold due to gravity. Place one every 2 feet. -
Address Problem Areas
Pipes passing through exterior walls: insulate inside the wall cavity if accessible. Hose bibs: install insulated faucet covers ($3-5) on all exterior hose bibs. Pipe hangers and supports: wrap foam around the pipe at hanger contact points -- bare metal hangers conduct cold directly to the pipe. Long runs in crawl spaces: consider adding heat tape (thermostatically controlled electric heating cable) under the insulation for extreme cold climates.
Tip: Heat tape plus insulation is the gold standard for freeze-prone pipes. Heat tape alone without insulation is wasteful. Insulation alone in extreme cold may not be enough. Together they are nearly foolproof.
Pro Tips
- Self-sealing foam insulation (with adhesive on the slit) costs slightly more but installs much faster and stays closed without tape.
- For hot water pipes, insulation with a higher R-value (thicker walls) saves more energy. Standard 3/8-inch wall is fine for freeze protection. 3/4-inch wall or double-layering is better for heat retention.
- Insulate the first 6 feet of the cold water inlet pipe above the water heater too. Convection currents can pull heat out of the tank through the cold pipe even when no water is flowing.
- Condensation on cold water pipes in summer can drip and cause water damage or mold. Insulation stops this by keeping humid air away from the cold pipe surface.
- Check insulation annually. Mice and squirrels in crawl spaces love to chew foam insulation for nesting material.
When to Call a Pro
Pipe insulation is always DIY. But if pipes are inside closed wall cavities and you suspect freeze risk, a plumber can reroute them or install heat tape inside the wall. If you have already had a pipe burst from freezing, have a plumber assess whether the pipe layout needs redesign, not just insulation.