Over the years we have installed and supplied hundreds of wood fired Hydronic Systems through out Australia and New Zealand…
This web page is set up to address the most common issues and solutions
Keep this page saved - it will be updated consistently...
A wood fired Hydronic system works like this
Understanding the Heart of your system - The Pump / Thermostat
The Hydronic Pump & Thermostat is the Heart of everything – its purpose is very important to the performance of your cooker / boiler and the temperature of your radiators
Every wood fired boiler or cooker - the "Fire" needs time to re-heat the water
To do this - the thermostat is there to tell the pump when to turn off and on. This gives your Boiler/Stove time to recover and re-heat the water
The Pump is controlled by a thermostat - that will allow your Pump to "Cycle" off and on
A "Cycle" of pump turning off and on can be like this :
As you start your system up, the house is normally cold, the water is cold, the stove is cold… it takes time to heat all this up
But once your system is heating up – the maintaining of the heat gets easier and easier
Wiring of the thermostat seems to be the most common issue in Wood Fired Hydronic Systems
No mater what brand of thermostat you use, it needs to be wired up so when the set temperature is reached – it then activates the pump.
If you install your system with out the thermostat – so the pump is consistently running; this will create a number of MAJOR issues like:
Have your thermostat set at 75oC… and wired up so the pump only activates when the water reaches this temperature: once the water temperature drops, the pump then turns off
Different brands have different wiring requirements -Check your wiring diagram on your thermostat manual
If you go to your pump when the stove is off an cold - your pump must not be on and running...
If it is - its obvious that your thermostat is not wired up correctly
Common issue No 2... Cold Water Return..
It might sound a little funny, but fire needs heat to burn at the right temperature.
When you light up your stove/boiler - every thing is cold and it takes time for the system to get to the optimal working temperature: but once your fire is burning at the right temperature, you see little to no smoke out of the flue, perfect glowing embers, no glossy residue in the firebox, nice light color ash...
The hot water jacket (or boiler) that surrounds the fire, needs to also have a minimum temperature to allow the fire to burn in the right conditions.
If the water in the boiler is returning too cold you will experience
A simple way to know what is going on in your system is to have installed a Hot and Cold Temperature gauges in your system
You are looking at the return water temperature to know what is going on in your system
The Optimum return temperature you want the water to return back to your boiler/cooker is a min of 50oC
There are two ways to achieve this
1. Calculate your hot water demand
If you run your system at under 70% capacity
(ie: you have a 10Kw boiler running 4Kw of H/water + 3Kw of Radiators = 7Kw... 70%)
If your thermostat is set between 75 - 85oC the water returning to your Boiler is estimated at 50oC
2. Pump Control Unit (Esse Mixing Valve)
This unit is designed to mix the hot water and cold water to guarantee the water returning to your system is at 50oC
Any system over 70% hot water demand capacity, we highly recommend you have one of these installed...
Q - My thermostat is set up right - but the radiators are not hot enough
A - This could be a number of reasons
1 - If you need heat - you need to make it
Most wood stoves/boilers use, on average, 4.6Kg to 6.8Kg of wood per hour to make enough heat to heat enough water to heat the radiators
2. - The radiators are not balanced
We have a good web page that will help you balance your system - check out HOW TO BALANCE YOUR RADIATORS
3. Your system is over specified
This is a very common issue. When the cooker/boiler specifications say it will heat...say 10Kw of heat...this is running your unit FLAT OUT - so like your car, you would never drive at 200Km an hour : like your stove, running it flat our will just chew up so much wood
On average, try to spec your system at 70% of the capacity - so a 10Kw boiler will comfortably heat 7Kw of water and use 4.6Kg of wood an hour
Q. My Water is boiling in my system - what do I do?
Turn your thermostat on your pump down.
Turn it down 5oC at a time until you get your boiler just under the boiling point...
Allow time for your boiler / water to settle. This may take an hour
Q. What Temperature should I run the system at?
What a standard temperature is - is 75oC... but this is a industry standard
What you are realy trying to achieve is the water returning to your cooker needs to be at 40 - 45oC MIN!!!
So if the water leaves your cooker at 75oC - it will heat your radiators to a nice temperature and return back to your cooker at 45oC ( Meaning you have a 30oC drop )
If the water returns too cold - it will cool down your cooker too much causing a number of issues
So you may find your thermostat may need to be set at 80oC or 85oC to achieve this
If your thermostat is set too high...you will get boiling.
The is not good - and sounds like a freight train in your house
If you get massive water hammering or water boiling turn your thermostat down by 5oC at a time
What you are trying to achieve is the "SWEET SPOT" somewhere between the water NOT boiling and the return temperature still at 45oC
Q. My Stove is sooting up - the hot water boiler is all glossy and shiny?
Your wood needs to be right
Most standard wood heaters you can get away with wood that is not "quite right"
But NOT with a wood stove or wood boiler
The comment "My wood is 100 years old" does not mean a thing - old wood can also get wet
The ONLY way to know your wood is with a Wood Moisture Meter...
You need to ensure the wood moisture is under 18%