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Drake 03-18-13 06:30 PM

Wood stove water heating?
Those that heat DHW or other uses to a storage tank with a wood stove can tank be over heated if stove is needed for space heating more than heating hot water? I know a pressure relief valve is an important part of the hot water loop but if tank reaches a max temp should a "shunting" loop be needed to prevent relief valve from releasing water if you still need to space heat?

Daox 04-02-13 03:41 PM

Doh, must have missed this post a while back.

I don't know of anyone using wood just for DHW. Everyone I know that uses wood is using it to heat their house. The secondary purpose of their wood heating is DHW useage. The DHW tank has its own circulating pump so it keeps its temperature up. Any extra heat from the wood boiler simply gets dumped into the house.

peacmar 06-07-13 09:45 AM

dhw from wood
Wish I had caught this. I heat my dhw with wood heat year 'round. Part of my plan to become independent of the grid. NO, and I repeat NO wood fired boiler should be aloud to reach temperatures above boiling when used in a domestic application. Your T&P valve on your water heater should not real ease until 90 psi or 200 degrees. Even the best heat exchangers will not be able to hear your water heater past 200 degrees even if your burner water temp is at boiling because there is too much heat lost throughout the system.

Dump zones are used where there is a potential for a chimney of a burner to create an uncontrolled fire during a power outage and that's about it. I'll explain all this when i get around to my burner build write up.

peacmar 07-15-13 01:48 PM

The best way to heat water with wood is with a gasifier and a well designed heat exchanger. I have reached far into the %90 range already. About %94 is my best so far. The problem.with the above product is that it steals heat from the chimney where combustion of gases is stilltaking place and there will eventually be a buildup of creosote. No non gasifier burner can burn clean enough to prevent this even with a catalyst.

Daox 07-15-13 02:09 PM

Any chance you could share more info with us about this gasifier you have made? We would really like to hear about it.

peacmar 07-15-13 02:38 PM

I most certainly will and have started a thread already but family constraints have made it hard to add any info lately. The basic explanation its that it's a down draft design with a dedicated secondary burn chamber and a three stage heat exchanger that resembles a modern high efficiency furnace. First rule is to burn as perfectly as possible, then extract every last bit of heat. I reach secondary combustion temps around 1800 on average leaving little matter behind. Only fine fly ash and very little of it.

oil pan 4 07-16-13 11:35 AM

In Maine I have seen people set a big coil of 1 inch copper water pipe next to their wood stove and plumb that piping in series with the regular hot water heater.

As long as the wood stove is going the hot water heater almost never comes on.

It as simple as anything you could hope for and works almost as good as anything you could buy.

peacmar 07-16-13 11:49 AM

This is a good one I have seen my uncle use something similar a this cabin in northern Wisconsin. Indirectly heat the water so there is no danger of over heating. My uncles method was to put a small 20 gallon electric water heater up near the ceiling but it is only used as a storage device. He then has a single loop of copper tube running down from the drain of the heater and into a T put in near the pressure relief valve. No pump, only convection currents. His coil goes All the way to the floor, up the back, then is suspended about an inch over the top of the burner. As long as there are no dips to form a heat trap the water will rise up into the heater as it is warmed. As the delta T nears equal the convection slows down and eventually the water stops circulating because heat is lost into the air around the coil just as fast as it is absorbed. Takes a little adjustment to get right but easy to do.

Drake 07-19-13 09:29 PM

My particular glass front wood stove has a space between the double wall top that I could form a loop of soft copper and slide between and plumb to storage or use as preheat for DHW. It would not require any modifying of the stove itself. What might be the way to control a loop pump so that it circulates just when the stove is hot? Simple convection design would impractical in my situation.

peacmar 07-19-13 10:44 PM

I would think that you may want a circulator to run constantly while burning wood if I'm understanding your explanation properly. Without convection you would have the opportunity for hot spots and steam to form and this could become dangerous. If your loop is large enough the excess heat would be dissipated in the house and not over heat the water heater and the pump could be turned off when the burner is out. Like an open circuit dhw heating system typically used with oil fired boilers. Flow controls could be used to slow the water flow enough to absorb the heat and allow it to heat the heater. This could be a multi purpose system to spread wood heat to distant rooms in the house even. It has great potential.

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