How Long Does It Take to Heat a Wood Fired Hot Tub?

A wood fired hot tub takes between 1.5 and 5 hours to heat, depending on size, starting water temperature and conditions. On an AlumiTub, expect around two hours for the Small, three for the Standard and five for the Large. The insulated aluminum structure and internally submerged firebox are what make it faster than a traditional wooden tub, and what keep the heat in afterward.

Heat-up time by size

Model	Water volume	Seats	Approximate heat-up from cold
Small, 5 ft	315 gallons	2 to 3, or 3 to 4 on Electric	~2 hours
Standard, 6 ft	420 gallons	4 to 5, or 5 to 7 on Electric	~3 hours
Large, 7 ft	650 gallons	6 to 8, or 9 to 10 on Electric	~5 hours

Ideal soaking temperature is 101 to 104°F. Once there, an AlumiTub holds heat with as little as an armful of wood a day, which most traditional wooden tubs cannot match.

Sunday morning 8am. Hadn't added a log for 11 hours and it was still 103.

Marc Young, Bowyer Island BC

Four things move the number:

• Outdoor temperature and wind
• Starting water temperature
• Firewood quality and dryness
• Insulation and how consistently the lid is used

Why an AlumiTub heats faster than a traditional wooden tub

Traditional cedar tubs without a lining lose heat through the walls and base once the wood becomes saturated. Wet wood lets heat pass through, which means longer heat times, more firewood, and faster loss between soaks.

An AlumiTub is built differently:

• A marine-grade aluminum structure that does not absorb water
• Three layers of insulation: 3.5 inches of rigid board beneath the base, 360 degrees around the tub, and a floating layer on the water surface, topped with an insulated lid
• An internally submerged firebox, the largest of its kind, heating the water directly and taking regular-length logs

Unlike an external firebox, an internal one uses natural convection to heat the water directly. That cuts heat time, uses less firewood, and produces minimal smoke when the wood is dry.

How to heat it, step by step

Fill the tub before lighting the fire. Fill to the line marked on the tub, or at least 4 inches above the chimney collar, and keep the water there the entire time the firebox is hot. Firing below that line warps the firebox, risks fire and structural damage, and voids firebox coverage.

1. Build the fire at the rear of the firebox, below the chimney, starting with paper and kindling
2. Allow airflow. Keep the firebox lid open about 4 inches while starting, then align it with the internal baffle
3. Build gradually. Add small pieces as the fire establishes, then larger logs. Do not load wood above the internal pipes
4. Stop adding wood at 95°F. The fire keeps transferring heat as it burns down
5. Let residual heat finish the job. The water rises to 101 to 104°F without overshooting

Adding wood past 95°F is the usual cause of an overheated tub, which then needs cold water to bring it back down. Never drain below the fill line until the firebox has fully cooled.

Five ways to heat it faster

1. Insulate the base

Two layers of rigid insulation beneath the tub, 1.5 inch and 2 inch for about 3.5 inches total. This is required on concrete, gravel and pressure-treated wood as a protective barrier, and owners report noticeably faster heat times. The bottom band accessory hides the edge.

2. Use the lid and the floating insulation

Place the insulation sheet on the water and the cedar lid on top, while heating and between uses. Overnight loss then comes down to two to three degrees Fahrenheit.

I can't believe the tub stays so hot. It heats so easily and the next morning when we went to use it, it had only dropped 3 degrees. It's well insulated and well made.

Jess Krutz

3. Keep the wall insulation intact

The insulation between the aluminum structure and the cedar cladding is what holds heat through a long soak.

4. Burn only dry firewood

Dry, seasoned hardwood burns hotter and cleaner. Wet wood spends its energy evaporating moisture, which means smoke, poor combustion and slower heating. More in the best firewood to use.

5. Stir the water

Use a paddle or a length of wood about four feet long to circulate water from the base. This distributes heat evenly and speeds the whole process.

Using both heat sources

If speed matters, the Hybrid carries the wood fired system and the electric heating and filtration system in the same tub, managed from the touchpad or an app.

Running both together shortens heat-up considerably, and it suits guest properties, residential installations, and anyone who wants the tub ready without tending a fire. A common approach is to hold a low baseline on electric, say 80°F, and bring it the rest of the way by fire.

One thing to know: keep the wood stove from taking the water past 106°F on a Hybrid, or the touchpad throws an error and the electrical system needs resetting.

On an Electric, heating from a cold fill takes up to fourteen hours at roughly three degrees Fahrenheit an hour, so it is designed to hold a temperature or run on a schedule rather than be heated on demand. There is no overnight drop to plan around, since the system holds whatever you set it to. More in the cedar tub that stays hot.

Why speed is not always the goal

It is entirely possible to heat a wood fired tub quickly. Speed is not the heart of it though.

A wood fired tub invites a slower rhythm: chopping wood, filling the tub, stoking the fire, letting anticipation build. It is the difference between instant coffee and a French press on a Sunday morning.

There is a particular satisfaction in tending a fire, listening to it crackle, and easing into water you warmed yourself. The ritual is part of the reward.

Explore the Wood Fired hot tub, or read the Ultimate Guide to Wood Fired Hot Tubs.