Buying Guides
Energy Efficient Entry Doors: What Makes One Keep the Heat In
A door loses heat through its slab, its glass, its frame and the gaps around it. Here is how each part works, what U-factor, R-value and Energy Rating mean, and how ENERGY STAR Canada fits in.
By EHI Custom Doors
Key Takeaways
- Natural Resources Canada says windows, doors and skylights together can account for up to 35 percent of a home's heat loss. Air leaks and poor installation often matter as much as the slab.
- An insulated core helps. Typical fiberglass and insulated steel doors run about R-5 to R-6, wood less, and our foam core is specified at six times the insulation of a traditional wood door.
- ENERGY STAR Canada (Version 5.0) asks for a U-factor of 1.22 W/m²K or lower, roughly R-4.7 for the whole door, or an Energy Rating of 34 or higher, with air leakage of 1.5 L/s/m² or less.
- You can find leaks with an incense-smoke test on a cold, windy day. New weatherstripping fixes a worn seal, not a warped door or a frame out of square.
- Ask any maker for the tested rating of the exact door and glass you are buying, because certification belongs to a specific tested door.
Energy efficient entry doors keep heat in by doing three things well: insulating through the slab, sealing every gap, and being installed tight to the opening. A door with a great core and a bad fit still leaks. This guide explains where a door loses heat, what the ratings mean, and how to choose one.
We are EHI Custom Doors. We manufacture and install custom fiberglass front doors and back doors, and we build each one to your measured opening.
Where a Door Loses Heat
| Path | What happens | What helps |
|---|---|---|
| The slab | Heat conducts through the door panel | An insulated foam core |
| The glass | Panes conduct more heat than an insulated slab | A good glass unit, and only as much glass as you need |
| Edges and frame | Air leaks through gaps around the door | A tight fit and good weatherstripping |
| Threshold and sweep | Air and water pass under the door | A sealed threshold and a sound sweep |
| Around the frame | Gaps between the frame and the wall let air in | Careful installation and insulation around the frame |
| Centre seam on a double door | The gap between two leaves can leak | A tight astragal and bolts that pull the leaves together |
Natural Resources Canada says windows, doors and skylights together can account for up to 35 percent of a home's heat loss, and that a poorly installed product can cause cold drafts even when the product itself is energy efficient.
Insulated Core: What the Numbers Say
Natural Resources Canada says doors with an insulated core are more thermally resistant than doors made of a solid material such as wood. Independent guides put a typical insulated fiberglass or steel door at about R-5 to R-6 or higher and wood lower, at about R-2 in one guide. Our CFC-free polyurethane foam core is specified at six times the insulation of a traditional wood door.
A slab rating is not a whole-door rating
An R-value quoted for a slab describes the panel. The whole door also includes glass, the frame, the seals and the threshold, and it is usually lower than the slab alone. That is why energy ratings are measured on a complete tested door.
U-Factor, R-Value and Energy Rating Explained
| Measure | What it tells you | Better is |
|---|---|---|
| U-factor (W/m²K) | How fast heat flows through the whole door for each degree of temperature difference | Lower |
| R-value | How well a material resists heat flow | Higher |
| Energy Rating (ER) | A unitless score that balances heat loss, air leakage and passive solar gain | Higher |
| Air leakage (L/s/m²) | How much air passes through the closed door | Lower |
U-factor and R-value are two ways of saying the same thing. In imperial units, R is about 5.678 divided by the U-factor in W/m²K, so a whole door with a U-factor of 1.22 works out to about R-4.7. Energy Rating cannot be converted directly to R, because it also counts air leakage and solar gain. Compare like with like, and ask for the rating of the complete door. For other door words, see our exterior door terms glossary.
ENERGY STAR Canada and Doors
ENERGY STAR Canada certifies windows, doors and skylights under a technical specification from Natural Resources Canada. Version 5.0, effective January 1, 2020, uses one national standard with no climate zones. A door qualifies with a U-factor of 1.22 W/m²K or lower, or an Energy Rating of 34 or higher, and air leakage of 1.5 L/s/m² or less. The rating comes from testing a complete unit, so certification belongs to a specific door and not to a brand.
- Ask the maker whether the exact door and glass you are quoting is ENERGY STAR certified, and get the answer in writing.
- Ontario's Home Renovation Savings Program lists $100 back per rough opening for ENERGY STAR certified doors, when the door is part of a bundle that starts with a home energy assessment. Our guide to custom exterior doors cost in Toronto covers the rebate and the City of Toronto loan program.
Air Leakage: The Hidden Loss
Natural Resources Canada suggests holding two or three incense sticks together near the suspect spot. Powerful leaks make the smoke dissipate and the tips glow, and leaks are easier to find on a cold, windy day. Check around the door, including the threshold and the door frame.
NRCan also describes the usual fix. Weatherstripping comes as flat strips, tubes and V-strips that work under compression or by sliding, and door sweeps are easier to install than a threshold and more durable, though they often seal less well. Weatherstripping cures a worn seal on a sound door. It does not cure a warped slab or a frame that has moved out of square. If a draft returns after a new seal, read our guide on when to replace an exterior door.
Installation: Where Efficiency Is Won or Lost
A door can only seal as well as it fits. Ours is built to your measured opening, with the frame and slab made as a matched set, and our own installer takes the final measurements and installs it. That removes the shims-and-foam compromises common when a stock size meets a crooked opening. Our guide on custom doors vs stock doors explains the fit advantage, and you can browse the door catalogue and photos of doors we have installed to see the range.
Glass, Sidelights and Transoms
Glass brings daylight, and it also loses more heat than an insulated slab. The number of panes, Low-E coatings, gas fill and spacers all change a glass unit's performance. Our guide to exterior door glass options covers those details, so ask for the glass unit on any quote.
Will an Efficient Door Save Money?
It can, but we do not promise a number. The 35 percent figure covers windows, doors and skylights together, and a door's share depends on your home, its size and how leaky the old door was. A tighter door also makes the entry feel warmer and cuts drafts, which you notice sooner than a bill. Our guide to fiberglass vs wood vs steel doors compares the materials on insulation as well.
What to Ask Before You Buy an Energy Efficient Door
- What is the core made of?
- What tested rating applies to this exact door and glass: U-factor or Energy Rating, and air leakage?
- Is this exact door ENERGY STAR certified?
- How are the frame, threshold and centre seam sealed?
- What are the sidelights and transoms rated at?
- Who installs the door, and how do they seal and insulate around the frame?
Get a Quote for a Tight-Fitting Door
Send photos of your entrance. Call EHI Custom Doors at 647-952-2311 or request a quote. We are open Monday to Sunday, 9 AM to 5 PM, and there is no pressure to book on the spot. See what customers say on our reviews page.
Energy efficient entry doors are a package: an insulated core, a good glass unit, tight seals and careful installation. Ask for the tested numbers for the exact door and check the fit at the opening.
Frequently Asked Questions
What makes an entry door energy efficient?
An insulated core, a good glass unit, tight seals and threshold, and careful installation. The whole door has to be tested, because air leaks and glass often matter as much as the slab.
What is a good U-factor for an entry door?
ENERGY STAR Canada Version 5.0 asks for a U-factor of 1.22 W/m²K or lower, or an Energy Rating of 34 or higher, with air leakage of 1.5 L/s/m² or less. Lower U-factor means less heat loss.
What is the difference between R-value and U-factor?
They describe the same thing from opposite directions. R-value is resistance to heat flow, so higher is better. U-factor is heat flow, so lower is better. In imperial units R is about 5.678 divided by the U-factor in W/m²K.
Are fiberglass doors energy efficient?
They can be. A foam core insulates well, and Natural Resources Canada says insulated-core doors resist heat flow better than solid doors. Glass, seals and installation also decide whole-door performance, so ask for the tested rating.
How do I find air leaks around my front door?
Hold two or three incense sticks together near the edges, the threshold and the frame on a cold, windy day. Natural Resources Canada says powerful leaks make the smoke dissipate and the tips glow.
Will new weatherstripping fix a drafty door?
If the door and frame are sound, a new seal or sweep often does. If the draft returns, the slab may be warped or the frame out of square, and replacement is the fix that lasts.
Is there a rebate for an energy efficient door in Ontario?
Ontario's Home Renovation Savings Program lists $100 back per rough opening for ENERGY STAR certified doors, as part of a bundle that starts with a home energy assessment. Check the current terms before you order.
Does the glass in a door affect energy efficiency?
Yes. Panes conduct more heat than an insulated slab, and the number of panes, coatings, gas fill and spacers change the result. Ask for the glass unit and the tested rating for the whole door.
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