Last updated: June 2, 2026
Hot Water Aboard!
Easy ways to raise your boat’s water temperature.
At the end of a wonderful day aboard, a hot shower is like heaven. That hot shower is even better when you don’t have to lug your towel, clean clothes, shower shoes, soap, and shampoo all the way up the dock to the marina washroom. And that marina shower isn’t an option when you’re swinging on the hook at a secluded anchorage. Hot water aboard your boat is greatly appreciated for showers, washing dishes and clothing, or rinsing off the salt after a swim from the aft deck. There are many options for hot water, including a water heater, but you need to be aware of a few things first.
It is important to know how much hot water you need aboard your boat. First, let’s talk about how it is heated. Your house ashore may have a 40-gallon or larger water heater. Most residential homes use either gas or electrical heating elements. The usual temperature for your home water heater is around 120 degrees Fahrenheit. A typical shower water temperature may average 105 degrees Fahrenheit. So, let’s think about how that water comes from the tank to you. When you adjust the hot and cold faucets, you are testing the temperature to satisfy your personal comfort.
Heat Sources
On your boat, the water may be heated by one or both of two heat sources. The first source is electricity. If your water heater is electrically powered, then it uses 110 or 220 volts of Alternating Current (AC). The electricity is either supplied by the shore power at the marina or your onboard generator when at anchor or underway. Be sure to turn the water heater circuit breaker on or you’ll be disappointed with a cold shower.
Your boat’s water heater may also be supplemented by the propulsion engine. The engine coolant is directed through a hose from the propulsion engine to the water heater in a closed loop.
This is an easy idea to understand. The engine gets hot from the combustion cycles. The coolant, aka anti-freeze, cools the engine through a closed loop. The liquid coolant recirculates through a heat exchanger that uses raw water to cool the liquid and then back to cool the engine again.
Take that same hot coolant and send it to the domestic water heater in an optional closed loop. The heat from the hose of the hot coolant enters the water heater. The heat transfer
occurs inside the water heater tank, heating the water inside the tank just like a heat exchanger. This is a great use of the hot coolant. This process doesn’t take any more energy or electricity to heat the water.
Too Hot to Handle
However, there are serious results to consider. The water in the tank may be as hot as the engine temperature. It’s possible to have water nearing 180 degrees Fahrenheit, much higher than your home water heater. Not only should you be aware of this, but also warn your guests so they don’t burn or scald themselves when showering or washing their hands.
Another result is that you will probably use less hot water when showering, doing laundry, or doing dishes in the galley. And, you will not need to waste water when you adjust the temperature waiting for hot water to arrive. It’s there in a jiffy!
Once you have learned this is an advantage, you can use the higher water temperature to extend your nice hot shower instead of taking the fabled “Navy Shower” not just to save water but to extend the hot water availability for the rest of your crew.
Water Heater Options
If your boat has the feature of using hot engine coolant to heat the domestic water, you may be uncomfortable with such extreme temperatures. Or you may just want the option to turn this feature on or off. It’s a simple task that’s easy to learn.
You can turn off the coolant loop to the water heater tank by locating the two valves on the engine system. Follow the two heater hoses from the water heater back to the engine and turn off both valves. This prevents the hot coolant from heating the water tank. It also provides you a method of isolating the engine from the water heater in case there is a hose rupture. You are back to heating your domestic water by shore power or generator electricity, and you can safely continue your cruise.
Chris & Alyse Caldwell
Captains Chris & Alyse Caldwell are USCG 100-ton Masters and cruising coaches who offer personal boat training online or on board your boat anywhere. The Caldwells help build your cruising confidence with hands-on training, with their AskCaptainChris.com training videos, through two-day seminars filled with tons of tips for the boater who loves learning, and now remote learning. If you have additional questions for Captains Chris or Alyse, please email them at chris@captainchrisyachtservices.com.
