Insulated hot tub cover: use, maintenance and replacement

Short answer: the insulated cover is the most underrated part of a hot tub. Heat escapes mainly through the water surface, so a well-fitting, insulated cover limits heat loss, evaporation and consumption of water treatment products, while keeping out leaves, insects and rain. The rules are simple: put it on whenever the tub isn't in use, never stand on it, brush off snow, and let the underside dry regularly.

Why the cover makes such a difference

Heating water costs energy (litres x degrees / 860 = kWh), but retaining heat costs almost nothing when the surface is sealed. Without a cover, water constantly evaporates, and evaporation is the fastest way to lose heat; full wind exposure doubles that effect. With an insulated cover:

• The water stays warm between sessions: topping up the heat the next day from, say, 30 °C costs a fraction of a full firing.
• Less water evaporates: less topping up and a more stable water balance.
• You use less water treatment product: sun and evaporation break down disinfectant.
• The water stays clean: leaves, pollen, dust and insects stay out.
• The tub is safer: a covered tub is less accessible to children and pets, although a cover never replaces supervision.

How to use the cover

1. Put it on immediately after every use: not "later", but while the water is still up to temperature.
2. Also during heating: this noticeably saves time and wood; see hot tub heating time.
3. Lay it flat and fully closed: a cover that's half on the rim lets just as much heat escape through the gap as an open corner.
4. Lift it with two people for a large tub, or use a cover lift. Dragging it over the rim damages the underside and the seams.
5. With a wood-fired heater: the cover covers the shell, never the heater or the flue. With an internal heater, watch the gap between the cover and the flue pipe.

Maintenance

After a long period closed, let the cover air out and dry for a few hours on a dry day now and then: moisture drawn into the core is the main reason a cover becomes heavy and loses its insulating value.

What never to do

• Stand, sit or lean on it: the foam core can't bear weight and sags permanently.
• Leave snow on it: the weight deforms the core and pushes water into the seams.
• Drag it over the rim or over tiles: damages the underside.
• Use a pressure washer or aggressive cleaning products: these damage the outer material.
• Apply undiluted chlorine or other chemicals to the underside: dose products only into the water, with the cover open.

When to replace it

A cover lasts for years, but not forever. Replace it when:

• the core feels heavy and waterlogged (the cover is noticeably harder to lift than when it was new);
• it sags or no longer closes flat against the rim;
• the underside is permanently mouldy or seams are coming apart;
• the tub cools down noticeably faster than before, with no other cause.

A saturated core barely insulates anymore; the difference in firing costs usually pays back a new cover within a season.