What's the best DIY way to reduce heat loss through garage doors?

Short answer

The best DIY way to reduce heat loss through garage doors is to first stop air leaks with new top/side weatherstripping and a tight bottom seal or threshold, then add rigid-foam insulation to the door panels. This two-step approach tackles the biggest losses—air infiltration and conduction—without overloading the door or compromising operation.

Why this works

• Air infiltration around the door perimeter can account for the largest heat loss in a garage. New seals and a threshold make an immediate difference.
• Panel insulation raises the door’s R-value and evens out surface temperatures, which helps comfort and cuts heat loss.
• Done correctly, these upgrades take half a day, cost far less than a new insulated door, and are reversible.

Typical material performance (approx.):
- Polyisocyanurate (foil-faced): R-6.0 to R-6.5 per inch
- XPS: R-5.0 per inch
- EPS: R-3.5 to R-4.0 per inch
- Reflective bubble wrap: R < 1 (by itself)—use only as a radiant supplement

Materials and tools

• Weatherstripping (vinyl or rubber door stop for top/sides)
• Bottom seal (T-style or P-bulb to match your retainer) and/or garage door threshold kit
• Rigid foam board: 1–1.5 in foil-faced polyiso is a great choice; XPS or EPS also work
• Foil HVAC tape (UL 181) for seams/edges
• Garage door insulation retention clips (optional) or compatible construction adhesive (foam-safe)
• Caulk (silicone or high-quality exterior sealant)
• Backer rod (for large perimeter gaps)
• Fasteners: exterior screws or ring-shank nails for weatherstrip
• Tools: tape measure, utility knife with fresh blades, straightedge, fine-tooth handsaw or insulation knife, drill/driver, stapler (optional), tin snips (for aluminum threshold/retainer), silicone spray, rags
• PPE: safety glasses, cut-resistant gloves, hearing protection if cutting metal

Step-by-step

1) Inspect and plan (15–30 minutes)

• With the door closed, look for daylight at the sides, top, and bottom. Note any warped jambs or damaged retainers.
• Measure the depth of each door panel cavity and choose foam thickness that fits without bulging.
• Identify your bottom seal profile (T-style, bulb, etc.). If the aluminum retainer is bent or split, plan to replace it or add a threshold.

2) Air-seal the perimeter (45–90 minutes)

• Top/sides: Remove old brittle weatherstrip. Install new vinyl/rubber door stop so the flexible fin just kisses the door face when closed—snug but not binding.
  • Start at the top, then the sides. Pre-drill if using screws. Keep a continuous line to avoid gaps at corners.
• Bottom: If using a new bulb seal, slide it into the retainer channels. A little silicone spray helps. Trim to length and cap the ends with sealant.
  • If the floor is uneven or the retainer is bad, install a threshold kit on the slab with adhesive. Close the door onto the threshold to set alignment and weight it until the adhesive cures.

3) Insulate the door panels (60–120 minutes)

• Choose foam: Foil-faced polyiso offers the best R per inch and a built-in vapor retarder. Face the foil toward the garage interior.
• Cut pieces: Measure each panel cavity individually—sizes vary. Cut foam slightly oversize for a friction fit.
• Fit and secure: Press foam into each cavity so it sits flush with the panel edges, avoiding hinges, rollers, and struts.
  • Use retention clips (included in many kits) or small dabs of foam-safe adhesive. Do not use solvent-based adhesives that melt foam.
• Tape seams/edges with foil tape to reduce air wash and protect edges.
• Optional: Add thin brush seals at section joints if available for your door model, but do not obstruct hinge movement.

4) Seal small gaps and penetrations (15–30 minutes)

• Caulk around track brackets, framing-to-wall joints, and any wire/pipe penetrations nearby. Use backer rod for gaps over 1/4 in.

5) Check balance and opener settings (10–20 minutes)

• With the opener disconnected, raise the door halfway and release. A properly balanced door should stay put or drift slowly. If it slams or shoots up, added weight has changed spring balance.
• Reconnect opener and reduce downforce if needed. Test safety reversal with a 2x4 laid flat.

Safety notes

• Springs are under extreme tension. Do not loosen or adjust torsion springs yourself. If balance is off after insulating, call a garage door pro.
• Unplug the opener while working. Use locking pliers clamped on the track to keep the door from moving.
• Watch clearances around cables, rollers, and hinges. Never block photo-eyes or travel paths.
• Cut foam on a stable surface with sharp blades. Wear eye protection and gloves.

Costs and time

• Weatherstripping set (top/sides): $25–$60, 45–60 minutes
• Bottom seal or threshold: $20–$120, 30–60 minutes
• Foam panels and tape or an insulation kit: $70–$120 for single door; $140–$220 for double; 1–2 hours
• Total DIY: typically $150–$350 and 3–4 hours for a double door

Tips for best results

• Prioritize a perfect seal at the bottom—uneven slabs benefit most from a threshold.
• Keep added weight low (ideally under 10–15 lb for a double door) to avoid spring adjustments.
• In cold climates, polyiso performs well in garages because the foil face reduces radiant loss; tape all edges to limit condensation inside the panel.
• If your door has windows, add interior magnetic storm panels or clear acrylic inserts to cut losses there.
• Improve the adjacent envelope too: insulate/air-seal the garage-to-house door, the garage ceiling under living space, and any exposed ducts.

Common mistakes to avoid

• Using fiberglass batts—they sag in moving panels and can interfere with hinges.
• Covering hinges, rollers, or struts with foam—causes binding and premature wear.
• Over-tightening perimeter weatherstrip so the door binds.
• Ignoring balance after adding insulation.
• Relying on reflective bubble wrap alone—minimal benefit without an air gap.

When to call a pro

• The door becomes hard to lift, won’t stay halfway, or the opener strains—springs likely need adjustment.
• Damaged tracks, cables, or bent panels.
• You want to upgrade to a high R-value insulated steel door (R-12 to R-18); the fit and spring selection are best handled by a garage door specialist.

By combining tight air sealing with well-fitted rigid foam and ensuring the door still operates smoothly, you’ll get a noticeable comfort boost and lower heat loss without replacing the door.