Storm Windows Benefits

Improved condensation resistance.
Increased resident comfort.
Reduced heating costs.
Reduced moisture damage.
Improved overall serviceability of windows.
Increased resident satisfaction with windows.
Considerations

Improved performance of single-glazed windows.
Single-glazed windows are often the major cause of heat loss in suites.
Condensation will occur between the two windows if the window on the interior side is not tightly sealed. Sealing/regasketing the interior unit should be specified as part of the work. Condensation will occur between the panes, and over time damage the paint, encourage the growth of mold and mildew, and rot window sills.
As interior storm windows reduce access to windows for ventilation, they may be removed by the residents and underutilized.
Implementation

Requires the services of a qualified contractor.
Ensure that bidding contractors have visited the site.
Quotations for performing work should include specification of the proposed units and the reasons for their selection, plus any special considerations.
Interior storm windows with magnetic seals can be easily installed.
Exterior storm windows must have an opening sash and insect screens.
Exterior architectural appearance is more easily maintained when interior storm windows are used.

Payback:

The cost of exterior storm windows is usually based on the area (ft2 or m2) of existing windows to be covered. Cost estimates can be derived from the following equation:

Cost = $1.20 x [width (inches) + height of window (inches)]

For a 48" wide by 60" high window:

Cost = $1.20 x (48 + 60)

Cost = $1.20 x 108

Cost = $130

The cost of interior storm windows with magnetic seals is about $15/ft2