Water vs air: how bed cooling systems work

The key takeaways

• Water conducts heat about 23 times better than air and holds about four times as much by weight, which shapes how the two kinds of bed cooling feel.
• Water-based systems change the temperature of the mattress surface and can take it below room temperature, because the water is chilled.
• Air-based systems blow air under the covers. Unless the air is chilled, it can only be as cool as the room.
• The Orion Sleep System is water-based, with a separate setting for each side of the bed from 50°F to 113°F.

Water carries heat about 23 times better than air

Water conducts heat about 23 times better than air, and it holds about four times as much heat by weight (Engineering ToolBox). That one difference explains most of what separates the two kinds of bed cooling system.

A water-based system runs chilled or warmed water through a thin cover on the mattress, so the surface you lie on changes temperature. An air-based system blows air under the covers, so it's limited by the air in your bedroom.

The Orion Sleep System uses water. Below, the two approaches side by side, how each works, and who each one suits.

Water and air, side by side

	Water-based	Air-based
What moves the heat	Water running through a cover under your sheet	Air blown under the covers
What you feel	A cooler or warmer mattress	Air moving across your skin
Below room temperature?	Yes, the water is chilled	Only if the unit chills the air
Where the unit sits	Beside the bed, joined to the cover by a hose	At the foot or side of the bed
Upkeep	Topping up and treating the water	No water to manage

Specific systems vary, so check the details for heating, temperature range and dual-zone control before you buy.

Inside a water-based system

There are two parts: a unit beside the bed and a thin cover on the mattress. The unit cools or warms a small reservoir of water to the temperature you've set, and a pump sends it through a hose into tubing inside the cover.

As the water flows under your fitted sheet, it draws heat out of the surface you're lying on, or adds heat if you've set it warm. Then it returns to the unit. That's why the unit gives off a little warmth into the room while it cools the bed: it's releasing the heat it collected.

Because water carries heat so well, a layer no thicker than a fitted sheet is enough to change the temperature of the mattress surface.

Inside an air-based system

An air system has a unit at the foot or side of the bed with a fan inside. The fan draws in room air and pushes it under the top sheet or through a ducted layer, across your body and out the sides of the bed.

Moving air carries heat away from your skin and helps sweat evaporate, though humid air slows that evaporation. Unless the unit chills the air first, the air going into the bed is the same temperature as the room. On a hot night in a warm bedroom, an air system moves warm air faster, but it can't bring the bed below room temperature.

Who water cooling suits

The difference shows up most for a few kinds of sleepers.

Hot sleepers in warm bedrooms

If your bedroom stays warm at night, the ceiling on air cooling is the room itself. Chilled water can keep the mattress under you cooler than the air around it.

Couples who want different temperatures

A water system with a separate connection for each side can run one side cool and the other warm on the same mattress. Each person sets their own number.

People who run cold some nights

A system that heats as well as cools covers winter nights and the chill after a warm spell. Check the heating range before you buy. Orion goes up to 113°F.

Who air cooling suits

Air is the better fit for some sleepers. If you like the feel of moving air on your skin, or your bedroom already stays cool at night, an air system gives you that breeze under the covers. There's no water to fill or treat, and air systems often cost less than water-based ones.

Questions to ask before you buy

• Will it fit your bed? You'll need to check your mattress size and depth, your bed base, and whether a split king is supported if you have one.
• How loud is it at the setting you'd actually use, and is there a quieter mode?
• Where's the unit going to sit, and will the hose or cord reach without getting in the way?
• What needs cleaning, refilling or replacing, and how often?
• Can each side be set to its own temperature, and can both of you control your own side?
• Which features work out of the box, and which need a paid plan?

Why Orion for water-based cooling

Orion is a water-based system for the mattress you already own, not a new mattress. Its Smart Cover lies on the mattress beneath your fitted sheet and is about as thick as a fitted sheet.

Two sides, one hose

The Control Tower heats or cools the water and sends it through the cover. A single hose, about 6.5 feet long, carries a separate connection for each side, which is how the two sides run at different temperatures, anywhere from 50°F to 113°F.

Schedules and Quiet Mode

You can schedule the cool-down before bed, change temperatures at set times through the night, and warm your side before you wake. Quiet Mode cuts the fan speed by about 25%, which also slows heating and cooling a little.

Water care and washing

Orion runs on distilled water. You top it up occasionally and add two cleaning tablets every six to eight months. The Smart Cover is spot-clean only, and your fitted sheet goes on top and washes as normal.

What comes with it

Heating, cooling, separate sides and schedules are included, with no subscription needed. Sleep tracking can be added-on, and the bed keeps heating and cooling if you cancel it.

Orion fits Queen, King and California King beds, on a standard frame or a single adjustable base kept nearly flat, but not a split king with two separate mattresses. The 30-night trial starts the day it's delivered.

Water vs air: quick answers

Are water or air bed cooling systems more effective?

They work differently. Water changes the temperature of the surface you lie on and can take it below room temperature, because the water is chilled. Air systems blow air under the covers and, unless the air is chilled, can only be as cool as the room.

How does a water-cooled mattress pad work?

A unit beside the bed cools or warms water, and a pump moves it through tubing in a thin cover under your fitted sheet. The water draws heat out of your body and cools the mattress surface, then it carries that heat back to the unit.

Which kind of bed cooling works for couples?

You'll want a system where each side has its own setting. The Orion Sleep System uses one hose with a separate connection for each side, so each person sets their own temperature from 50°F to 113°F.

Do bed cooling systems need a subscription?

Some features on some systems do. With the Orion Sleep System, heating, cooling, separate sides and schedules are included. Sleep tracking is an optional subscription called Orion Intelligence.

Want each side of the bed at its own temperature, on the mattress you already own? See how the Orion Sleep System works.