How to build a compost-heated shower


Looking for a more natural way to have warm showers? A compost-heated shower uses the natural heat to warm water for showering.

Compost-Heated Shower in Use
Dennis Carter’s wife, Anneli Sundqvist, uses the outdoor shower at the couple’s hostel
in Maine. | Courtesy of Dennis Carter

Dennis Carter and his wife Anneli Sundqvist have always strived to do everything a little bit outside of the mainstream methods at their hostel in Deer Isle, Maine.

So when Carter was researching alternative methods to heat the outdoor shower their guests — as well as he and his wife — use, the idea of using a compost pile as a heat source instantly caught his attention.

When he realized he could build the whole heating system for about $50, he was sold.

“We really try to make the whole yard, the gardens, the building setup and the energy systems alternative and paradisiacal at the same time. So to combine gardening and energy production with having a comfortable shower, [it] seemed like it would work really well for people,” Carter said.

From Memorial Day weekend to Labor Day weekend, the Deer Isle Hostel hosts about 10 guests per day — and they all have to shower somewhere.

How to build a compost-heated shower
In this drawing, the set-up of the piping within the compost pile can be seen.  | Courtesy of Dennis Carter

Initially, Carter thought about using a traditional electric heat source to heat the water that feeds into the outdoor shower. But he wanted to be more environmentally friendly than that, using a heat source that would remind people how much water they are using.

“If you’re outdoors taking a shower and it’s relaxing, people would just stand there and use 20 to 40 gallons of water,” Carter said.

After researching solar-heated showers, Carter stumbled upon a YouTube video about using a compost heap to heat the water that feeds into an outdoor shower, and he decided to adapt that method for use at the hostel.

Compost-Heated Shower temperature gauge
The compost heats the water up to temperatures between 100 degrees and 150 degrees. | Courtesy of Dennis Carter

Having built the first version of his compost-heated shower four years ago, each year Carter says he improves on the set-up. This summer the compost pile has heated the water up to temperatures between 120 to 150 degrees.

To heat your own outdoor compost-heated shower, as long as you’re willing to put in a day’s work getting the system together, the reward of a sustainably heated shower is well worth the effort, Carter said.  

“If you’re fairly confident with your compost building skills, it’s worth spending the $50 and trying it,” Carter said.

The materials required for the project include a traditional garden hose hooked up to your water source, about 200 feet of black poly-pipe that is a half-inch in diameter, a pipe-to-hose adapter and shut-off valves.

The compost pile Carter uses to heat the shower is 8 feet wide and 5 feet high. When he builds the compost pile he uses about a truck bed’s worth of wood chips and another truck bed’s worth of seaweed. Carter also uses, on occasion, weeds or vegetable scraps in the compost pile if they are on hand but does not use manure in this specific compost pile because it is for public use.

To start, run the garden hose from the water source to the area where your outdoor shower stall is located. Using the pipe-to-hose adapter, connect the hose to the poly-pipe and then begin building the compost pile just outside the shower stall.

Once a base layer of compost materials has been mixed covering an 8-foot area, Carter says to begin coiling two rounds of the poly-pipe on the pile. Holding down the piping with a brick, cover the piping with another layer of compost before laying down another two rounds of the piping. While constructing the compost pile, Carter recommends to form the pile like a dish, with the sides of the pile being slightly higher than the center so gravity can help the composting process.

Once the pile is 5 feet high and the piping has been coiled inside about 24 times, attach the end of the piping to the valve that feeds into the shower. Inside of the shower, Carter has a 2 gallon watering can attached to a pulley system to help hoist the can above a bather’s head. Carter has also added a second valve to the shower that feeds in cold water from a separate hose so people can blend hot and cold water.

While the water sits in the piping inside of the compost pile, the heat produced by the organic matter breaking down in turn heats the water. The 24 rounds of coiling inside the pile hold about 4 gallons of water.

With the water only being heated as it travels or sits in the piping buried in the compost, Carter tells his guests they have about 4 gallons of water that will be between 100 to 145 degrees. However, because the 2-gallon watering can provides a delay, an additional 2 gallons of water begins to warm in the piping while people use the first 2 gallons. So, Carter said, between 6 and 8 gallons of water can be warmed for an enjoyable shower.

Carter rebuilds the compost pile about three times during the summer, with the shower providing about six to 10 showers on any given day during the hostel’s season. Once the hostel closes for the summer, Carter and his wife will continue to use the compost-heated shower until mid-October.

Inside a compost-heated shower
Dennis Carter demonstrates how the outdoor shower is used at the Deer Isle Hostel. Carter and his wife Anneli Carter-Sundqvist started the hostel in 2009 with an emphasis on providing affordable and eco-friendly accommodation to people who travel to the area. |Gabor Degre 

The compost-heated shower is a favorite of hostel guests, Carter said. As a host, he’s just glad he gets to introduce something new into the lives of the folks who stay at his homestead.

“They get clean, they feel good and they feel good about the process,” Carter said. “There’s gotta be people who are politely quiet about it, but overall, it’s the most popular thing here and people comment about it constantly.”

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