Domestic Hot Water and Wood Cookstoves: What To Know

Domestic Hot Water with Elmira Stove - Obadiah's Cookstove Community
Many folks who want to live the self-sufficient lifestyle know how to handle their food: Hunting, gardening, and building a fire. Mastering the methods behind each of those tasks means you’ll never have to worry about starving, no matter the situation. But what about water? Specifically, hot water?

We all know water is more important than food for survival, but we don’t often think of the huge role that hot water plays in our day-to-day life. We should, though, because heated water is essential to minimizing bacteria in cooking, cleaning, and bathing. Of course, anyone can throw a pot on top of a stove or over a fire, but if you’re living in an off-the-grid household, your hot water needs will be much greater than any stove-top pot can offer. So what’s the solution?

Domestic hot water via stove.


Contents

Many woodstoves and cookstoves offer an option (typically for an additional but reasonable cost) for domestic hot water installations. Here’s how it typically works:

Water Jacket to Storage Tank

Domestic Hot Water - passive - Obadiah's Cookstove Community

Domestic Hot Water – Passive System.

A water jacket (also known as a “water coil”) is a block of steel that attaches to the back or side of your stove, and contains an entry and exit connection for piping. When water enters the block, it hits a chamber inside and slows down, allowing the water to become heated. This heated water is then forced out to your water storage tank, which is sitting above your stove.

The water jacket is connected by piping to the water storage tank. As cold water flows from the bottom of the storage tank and into the jacket, it becomes heated. That heated water is then sent back out through a separate pipe to the top of the storage tank, thus creating a tank full of hot water that can then be connected to where ever you need. This method relies on simple physics: Hot water rises, and cold water falls. As a result, no pump is necessary. This creates a thermoloop and is known as “thermosiphoning”, a passive system. You do need a specific valve to make thermosiphoning work, so make sure you use a brass swing valve. Do not use a check valve, especially one that is spring loaded, as it will not create enough pressure for the system to function. See this forum post for more information.

Domestic Hot Water - Pioneer Maid System - Obadiah's Cookstove Community

A passive system installation using a Pioneer Maid Cookstove.

Domestic Hot Water Installation - Cookstove Community

A thermosiphon setup.

For an example of a thermosiphoning set up, we have this installation from our friend Tim. Here, the tank on the left can be shut out of the system with valves, which helps to create hot water faster. To slow the creation of hot water, that tank can be activatied to allow longer burns before both tanks become overwhelmed with water that is too hot.

Note: Since this photo was submitted, the top of the second tank has been connected with hot water, and a tempering valve has been installed. You can read more about Tim’s installation in our forum on this post.

Keep in mind that some cookstoves can be ordered with a water reservoir in the form of a tank that fits onto the back of the stove. If a reservoir is not pressurized it cannot be connected to a domestic hot water system. They are fill and drain systems only, which means you fill it with a bucket and drain it into a bucket. If you buy a wood cookstove with a water reservoir and it is connected to a water coil when there is a fire in the firebox, there must also be water in the water reservoir, or it will melt. If you are going to use a water reservoir on a cookstove, it is best to look for one that has a water reservoir that is passively heated and can sit there empty until needed without a problem. This will eliminate many of the problems associated with the use of a reservoir when you have the luxury of turning a tap for hot water, but also need a back up source in case the power goes out. Hauling water to your stove in buckets is not easy, and it will seldom be used when it is easier to turn a knob for hot water. Over time the water will become stagnate or it will begin to boil and create steam, which can create mold and mildew in your home.

Pump System

Domestic Hot Water - active - Obadiah's Cookstove Community

Domestic Hot Water – Active System.

A pump system, by contrast, is an active system. This method of generating domestic hot water relies on an electric pump to create the thermoloop and a heat activated sensor to activate the pump when the stove is hot.

An active system can potentially produce more hot water and, as long you have power, there is less chance of dangerous pressure levels from the water overheating (the result of an active system producing more water movemnt). However, an active system can become complicated quickly: In the event of a power failure, an active system’s electric pump will cease and potentially lead to dangerously high pressure in the water jacket and piping. With this danger in mind, you must also install a relief valve within two feet of the water jacket that is piped to a drain.

Obadiah’s firmly believes that a passive system is the best way to go in terms of simplicity, safety, and expense. There may be circumstances where a pump system is the best (or only) option, but the benefits of relying on simple physics instead of electronics when attempting to live the self-sufficient lifestyle cannot be overstated.

Domestic Hot Water - Gravity System - Obadiah's Cookstove Community

This diagram shows a typical passive installation (sometimes referred to as a “gravity” system) for domestic hot water.

Is Domestic Hot Water Right For You?

So now you know the basics. The real question is, should you use your stove for domestic hot water? Depending on your circumstance, heating this way can be hugely beneficial. With a passive system there is absolutely no reliance on electricity, which will ultimatley keep your heating costs down during the cold winter months.

Kitchen Queen Water Coils - Obadiah's Cookstove Community

Water coils for a Kitchen Queen cookstove.

The key to using this type system is understanding that you cannot install valves to turn off the flow of water, or you will have an explosion when the water boils. When there is fire in the firebox of your stove, some of the BTUs will be going into the hot water tank, so you must have two ways to read the temperatures in the tank. If you don’t have a way to read the water inside the tank, you will need to install a temperature gauge on the inlet side of the thermoloop and on the hot side of the domestic hot water outlet on the tank, which will give you an idea of the temperature of the water going in and coming out of the tank. For example, if the water going into the tank on the thermoloop side is running at 220 degrees and the hot water coming out is 190 degrees, it means you have 20 degrees to go before the pop off valve will release and all your hot water goes down the drain.

The real catch with using your stove for domestic hot water is that it is a constant monitoring process. You will want to make sure you don’t blow your valve and lose your hot water by bleeding off the BTUs inside the tank when you use hot water at the tap, laundry, or shower. If you have a family, you can rotate your turns at showers and do laundry and dishes throughout the day to periodically use accumulating hot water. Another trick to get the most out of this system is to also drain the hot water tank at night (take showers, etc.), so that it will refill by morning.

This system works if you’re on a ranch, homestead, or farm, and everyone is around during the day. If everyone is going different places all the time, it won’t work because no one can monitor the water temperature. If that’s the case, the system has to be automated with aquastats, pumps, and a diversion system to bleed off BTUs into the something like a hot tub. These systems can get complicated quickly and the price can get expensive, so make sure you can run it with a battery back-up in case of a power failure.

So, how does all of this look in real life? If you worry that a domestic hot water installation will be a mess, fret not! Below are a few photos of a properly installed system that’s been connected to radiant in-floor heating.

By using your stove to heat water for domestic use, you will be taking a huge step towards total self-sufficiency. For more information on domestic hot water via stove, please check out our videos on the subject. There are also several free resources available online to help you understand a bit more about this unique way to heat your water:

The Cookstove Community also offers a basic installation walkthrough on our forums, check it out here if you need some advice on what to do next!

Obadiah’s Domestic Hot Water Kit

Not sure what parts you need to begin the process of getting a domestic hot water setup? Fret not! Obadiah’s has put together a comprehensive kit with everything you need for your system. Here’s what’s included:

First, select your boiler tank size:
Part # Part Price
GW 40 40 gallon Range Boiler Tank – Hot rock lined welded heavy gauge steel $475 (plus freight)
GW 80 80 gallon Range Boiler Tank – Hot rock lined welded heavy gauge steel $745 (plus freight)
Next, pick up Obadiah’s Domestic Hot Water Kit
Part # Part Name Price
36DT Dip Tube for hot Rock Range Boiler $35
2K501 1.1 gallon Expansion Tank $59 (plus freight)
34-BD 3/4″ NPT Boiler Drain $11
T571 Stick Style Thermometer Gauge $33
SV-150 150 PSI Safety Pressure Relief Valve 3/4″ NPT (2 units) $44
H25-18 Gauge Style Pressure and Temp Gauge $30
FV180/U 1/8″ NPT Auto Vent Valve $15
AM101-1 3/4″ NPT Mixing Valve $103

Total Price: $317.

Need to add a pump? Just include these parts (either on-grid or off-grid, depending on your living situation):

Domestic Hot Water Pump Parts (on-grid, 120 Volt AC System)
Part # Part Price
 006B Taco DHW Circ Pump 120 Volt Sweat $323
 L6006A  Aquasat Controller well type with stem $168
Domestic Hot Water Pump Parts (off-grid, 12 Volt DC System)*
Part # Part Price
C-12V Laing 12 Volt Circ Pump 3 gal per minute 1.9 amps 1/2″NPT $295
12VRELAY 12 Volt Relay for Circ. Pump $23

*Note: A 12 volt probe type thermostat is needed to activate the pump, installed to spec. based on system requirements.

Please note that these are general prices and are subject to change; all prices are provided for estimate purposes only.