# Do they have heat tape for a garage door bottom? Last reviewed: 2026-08-20 Reviewed by [The GarageDude Editorial Desk](https://garagedude.shop/authors/editorial-team/) The R-value on a garage door box is calculated through the centre of one section. It is not a measurement of the finished door. DASMA reports whole-door performance as a tested U-factor under ANSI/DASMA 105, and the two numbers are not reciprocals of each other — you cannot convert one into the other. R-value measures One section, calculated U-factor measures Whole door, tested Test standard ANSI/DASMA 105 Better number Lower U-factor ## The short version - R-value is calculated on the door section only. U-factor is tested on the entire installed assembly. - DASMA states plainly that "U-factor and R-value are not reciprocals of each other" for garage doors. - Section joints, stiles, hardware and seals create thermal shortcuts around the insulation that a section calculation cannot see. - U-factor testing follows ANSI/DASMA 105, which the IECC cites as the thermal test method for garage doors and which is based on ASTM E1423. - Lower U-factor is better. A door at U-0.20 is twice as thermally efficient as one at U-0.40. ## How does a garage door actually hold its own weight? A garage door is not lifted by the opener — it is lifted by the spring, and the opener only guides it. A residential door weighs 85 to 400 pounds, and the counterbalance holds that weight so the motor only has to overcome friction. That is why springs and cables are professional work while sensors and remotes are not: one group holds the stored energy and the other does not. [Garage door safety](https://garagedude.shop/safety/) covers the balance test and what an unbalanced door does to an opener. ## What is the one-minute test everyone should be doing? The reversal test, monthly, with a 2x4 laid flat in the door's path: it must reverse on contact. If it does not, stop using the opener until it is adjusted, repaired or replaced. It matters because this system fails silently — a door whose reversal has stopped working looks and sounds exactly like one that still does. CPSC recommends inspecting the door and opener every 30 days. [Children, pets and the garage door](https://garagedude.shop/safety/child-safety/) covers why the standard exists. ## At what point should I stop and call someone? - The door is very heavy by hand with the opener disconnected. The counterbalance has failed. - You can see a gap in the spring coil , or a cable that is frayed, slack, or off its drum. - The door sits crooked , higher on one side, or has come off its track. It is still under full tension. - The door does not reverse on the board test. The entrapment protection is not working. None of those is calling too early, and the rule worth teaching at home comes from that same federal text: “NEVER GO UNDER A STOPPED PARTIALLY OPEN DOOR.” ## Questions that come up next ### Does a door that reverses mean something is broken? No — the opposite. A door that stops and goes back up when it touches something is the entrapment protection doing exactly what 16 CFR 1211 requires. The fault worth investigating is a door that fails to reverse. ### Can I disable the photo eyes to get the door closed? No. That removes the external entrapment protection required since 1993, and it is the protection that exists because of the CPSC child fatality record. If a sensor is genuinely faulty, replace it — it is among the cheapest parts on the door. ### Is it safe to use the emergency release with the door open? The federally required manual text says to use it only when the door is closed wherever possible, because weak or broken springs may allow the door to fall rapidly. A great deal of DIY content advises the opposite. ### Should I replace one spring or both? If the door has two, quote both. The second is the same age and has taken the same number of cycles, so it is next. This is one of the few upsells in the trade that is genuinely honest. ## Common mistakes - Comparing one door's R-value against another door's U-factor. DASMA states the two methods are not comparable. You are comparing a calculation of part of one door with a measurement of all of another. - Taking the inverse of R-value to get U-factor. That works for a uniform material, not for a door assembly with joints, stiles and hardware conducting around the insulation. - Buying insulation value for an uninsulated, unsealed garage. The door is one surface. If the walls and the perimeter seal leak, the door's rating is not the constraint. ## Related questions - [Garage door safety](https://garagedude.shop/safety/) - [Insulation & R-value](https://garagedude.shop/questions/insulation-and-r-value/) - [Are amarr garage doors energy star certified?](https://garagedude.shop/questions/insulation-and-r-value/are-amarr-garage-doors-energy-star-certified/) - [Are chi garage doors energy star certified?](https://garagedude.shop/questions/insulation-and-r-value/are-chi-garage-doors-energy-star-certified/) - [Are energy efficient garage doors tax deductible?](https://garagedude.shop/questions/insulation-and-r-value/are-energy-efficient-garage-doors-tax-deductible/) - [Are r18 overhead garage doors energy star?](https://garagedude.shop/questions/insulation-and-r-value/are-r18-overhead-garage-doors-energy-star/) - [Are wood garage doors more energy efficient?](https://garagedude.shop/questions/insulation-and-r-value/are-wood-garage-doors-more-energy-efficient/) - [Can temperature change cause my garage door alarm go off?](https://garagedude.shop/questions/insulation-and-r-value/can-temperature-change-cause-my-garage-door-alarm-go-off/) ## Sources - [Technical Data Sheet 163 — U-factor and R-value for Residential and Commercial Garage Doors](https://www.dasma.com/wp-content/uploads/2022/09/TDS163..pdf) — DASMA Tier 2 accessed 2026-08-17 - [Technical Data Sheet 196 — U-factor and the DASMA Thermal Performance Verification Program](https://www.dasma.com/wp-content/uploads/2025/01/TDS-196.pdf) — DASMA Tier 2 accessed 2026-08-17 - [ASTM E1423 — Standard Practice for Determining Steady State Thermal Transmittance of Fenestration Systems](https://www.astm.org/e1423-21.html) — ASTM International Tier 1 - [International Energy Conservation Code](https://codes.iccsafe.org/) — International Code Council Tier 1