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Glazing & glass pack guide

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Double pane with Low-E and argon

Two panes of glass enclosing a single sealed cavity filled with argon gas, bonded by warm-edge spacer bars.

Glass pack cross-section

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What it is and how it is built

Two panes of glass are held apart at the edge by a spacer with a desiccant that keeps the cavity dry, and the unit is sealed around its perimeter. The cavity between the panes is filled with argon, and a Low-E coating sits on the side of a pane that faces the cavity.

Why you'd want it

A double-pane unit is the usual answer to keeping a room warm for a sensible price. With a Low-E coating and argon it suits moderate and warm climates and most rooms of a house, and it keeps the sash light enough to open easily.

A triple unit is warmer, but heavier and costlier; double pane is the glass to start from unless the winters are long and hard or the windows are very large.

Pros and cons

Pros

  • It keeps heat in far better than a single pane, at a moderate price.
  • The sash stays light, so it opens easily and puts less load on hinges and balances.
  • It is the standard make-up most manufacturers offer, so it is easy to compare between quotes.

Cons

  • In long, very cold winters it keeps the room-side glass cooler than a triple unit does.
  • On its own it does not make a room quiet: noise depends on the make-up of the glass.
  • Its comfort depends on the coating and the spacer: a plain metal spacer leaves the edge of the glass colder.

It's for you if…

  • Your home is in a moderate or southern climate zone with mild or normal winter heating periods.
  • You want a lighter window sash that opens smoothly and puts less strain on hinges and balances.
  • You want good thermal comfort without paying for the extra glass and weight of a triple unit.

Don't overpay if…

  • A salesperson pushes triple pane although your winters are mild and your heating bills are moderate.
  • The opening is a large operable casement or slider, where the extra weight of a third pane would strain the sash.
  • Your main goal is quiet: ask about laminated glass in a double unit rather than paying for a third pane.

How it affects the price

Double pane is usually the less expensive of the two glass units: it has one pane and one cavity fewer than a triple unit, and the lighter sash needs no heavier hardware.

Within double pane the price still moves: the type of coating, argon or krypton in the cavity, a warm-edge spacer, laminated or tempered glass and the size of the window all add to it. The market reference for installed windows is on the page of all glass options.

All glass options and their price references →

Lifespan and care

Clean the glass as usual with a soft cloth and a mild glass cleaner; the coating needs no care, because it is sealed inside the unit. Watch for fog or moisture between the panes: it means the seal of the unit has failed. In that case contact the manufacturer and check the warranty terms for the glass unit.

Figures with sources

Why argon or krypton fills the cavity
They block more heat transfer because they are denser than air; argon is the popular and affordable alternativeSource:Gas Fills — NFRC Consumer Guide to Windows (Efficient Windows Collaborative)
How much gas an efficient window loses
About 0.5% of gas fill per yearSource:Gas Fills — NFRC Consumer Guide to Windows (Efficient Windows Collaborative)
What a warm-edge spacer does
Blocks heat and cold from passing through a window by blending metallic and non-metallic materials; also cuts condensationSource:Spacers — NFRC Consumer Guide to Windows (Efficient Windows Collaborative)

What it pairs with

A double-pane unit works only as well as its coating: a Low-E coating suited to your climate decides how much heat stays in and how much of the sun's heat comes through. The frame carries the glass and seals around it, so choose the two together.

Which coating to choose →Which frame suits this glass →

Compared with the other glass unit

Frequently asked questions

Is a double-pane unit enough for a cold winter?

In most moderate climates, yes, with a Low-E coating, argon and a warm-edge spacer. In regions with long, very cold winters or for very large windows, compare it with a triple unit by the U-factor on the NFRC label.

What is the gas between the panes, and does it leak out?

It is usually argon, a gas denser than air that slows the movement of heat. A small share can leak out slowly over the years; a good perimeter seal keeps that loss small.

Why has the glass fogged up between the panes?

Moisture inside the unit means its seal has failed and dry air or gas has been replaced by damp air. It cannot be wiped away; contact the manufacturer and check the warranty terms for the glass unit.

Do I need panes of different thickness?

Only if noise matters to you: panes of different thickness, or laminated glass, damp the sound of traffic better than identical panes. For warmth alone, standard panes are fine; more on noise is on the page of all glass options.

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