5 Quick Fixes for Underperforming Heat Packs

Heat pack not getting warm enough—or dying mid-route? Most issues come down to oxygen, activation, placement, or insulation balance. Use this quick guide to diagnose the problem and fix it fast. For consistent, controlled warmth designed for live shipments and delicate goods, choose UniHeat shipping warmers.

Fix #1 — Give It Air: Improve Oxygen Flow

UniHeat warmers are oxygen-activated. Starved packs warm slowly, stall, or shut down entirely.

• Add vent holes to the outer carton (2–4 pencil-size). Do not punch the inner foam liner.
• Keep packs unwrapped—no plastic bags or airtight film. Use a paper sleeve if needed.
• Create an air gap around the pack; avoid compressing it under heavy void fill.

Fix #2 — Activate Properly (and Early Enough)

Cold-starting a pack inside a sealed box is the #1 cause of “no heat on arrival.”

• Pre-warm 20–30 minutes in room air before sealing. Gently shake to distribute contents.
• Check the clock: If your route is 2–3 days, choose a warmer that matches (e.g., 72hr).
• Verify temperature ramp: Packs should feel noticeably warm before they enter the carrier network.

Match duration to the route: 40hr | 72hr | 96hr

Fix #3 — Reposition the Pack (Stop Hot Spots & Cold Corners)

Wrong placement = uneven box temperatures, condensation, or pack stall.

• Tape the pack to an inner wall or lid using a cardboard spacer—never directly onto foam.
• Keep off direct contact with animals, plants, chocolate, or plastics that can soften.
• Distribute multiple packs on opposite sides in large boxes for even warmth.

Fix #4 — Balance Insulation vs. Ventilation

Too much insulation = oxygen starvation. Too little = heat loss.

• Right-size the shipper: Avoid oversized cartons that waste heat.
• Use foam or insulated liners but maintain small air channels for circulation.
• Add or reduce vents to tune performance based on route weather.

Fix #5 — Check Storage, Age, and Handling

Old or moisture-exposed packs underperform.

• Store sealed in a cool, dry place; avoid high humidity.
• Rotate inventory (first in, first out). Check lot dates.
• Inspect packaging—any broken seal or pinhole can partially activate and shorten lifespan.

Fast Troubleshooting Checklist

• Pack not warm after 10–15 minutes? Increase pre-activation time in room air.
• Pack gets hot, then cools? Add vent holes or reduce over-insulation.
• Cold corners on arrival? Reposition pack and add light breathable void fill.
• Route outlasts pack? Upgrade duration to 72hr or 96hr.
• Moisture inside box? Increase air gap, elevate pack placement, and avoid direct foam contact.

Frequently Asked Questions

Why does my heat pack feel warm outside the box but cool inside?

It’s likely oxygen starvation. Add 2–4 small vent holes to the outer carton and avoid sealing gaps completely with tape. Ensure the pack isn’t smothered by plastic or dense foam.

How long should I pre-activate a UniHeat pack?

Allow 20–30 minutes in room air before sealing. You should feel a steady heat ramp before boxing.

Which duration should I choose for 2–3 day winter routes?

Use the 72-Hour warmer; upgrade to 96-Hour for extreme cold or delay-prone areas. For short, overnight routes, the 40-Hour is often sufficient.

Can I use two shorter packs instead of one long-duration pack?

Yes—placing two shorter packs on opposite sides can improve distribution in large cartons. Ensure adequate ventilation and air gaps.

Do UniHeat warmers work for food, plants, and animals?

Yes. UniHeat was originally marketed for live insects, plants, and animals, and is now trusted for temperature-sensitive foods and other perishables that need consistent, moderate warmth.

Next Steps: Match your pack to the route and fix oxygen first. Explore the full line of UniHeat warmers: 40hr, 72hr, 96hr, or visit UniHeat.us.