Heating water is a great way to utilize the energy from a fire, and a wood fire is no different. This is a much more efficient process than making electricity from fire. A wood powered water heater can be very simple to build, and to operate, and can be relatively expensive.
My family has a remote cabin that is off grid. About a decade ago we bought a wood fired hot water heater and are still using it to this day. For occasional use, this unit is great. It is built similar to a gas water heater and works the same way. The difference is, instead of a gas burner at the bottom, there is a small wood burning firebox.
The water heater actually works great. We mostly use the larger slivers and chips of wood that tend to accumulate around the firewood splitter. They are easy to ignite and fit nicely in the small firebox. Although the small size of the firebox opening makes things a little awkward for building fires, it’s actually easy to get one going since it drafts well.
Once a fire is going we just keep an eye on it and put on more fuel when needed. After about 20 minutes or so the water is hot enough for a shower. At that point there is usually enough water for two showers and enough left over for washing dishes.
It is amazing how little wood it takes to heat this much water. As far as energy use, this unit works great. But the downside is convenience, or lack of convenience. For everyday use, it would become a chore to have to build a fire and wait 20 minutes before you can have hot water. So for a typical home, this is not going to fit in well with most people’s busy lifestyles. But for a situation like a remote vacation home, it works great. Most of the time in sunny weather, we don’t use the wood fired water heater. A solar shower is much more convenient when the weather is warm and sunny.
