WORKING OUT YOUR
Ok - so you’ve
decided you want a stove with a boiler to either replace of
supplement other forms of heating. In my opinion the first
most important rule is DON’T GET CARRIED AWAY BY SIZE. This is where a
vast amount of people go wrong. It is not all about buying the biggest appliance you
can afford. An excess of hot water - to either hot water tank or radiators (or both) can
either be very inefficient or very, very dangerous. Over production of hot water
could result in bursting of pipes and spewing of boiling hot water. See this link
for a document stating warning signs and issues relating to over production of hot water
It is far better to run
a system with slightly LESS water capability than it is too much. After all - if you are
producing an excess, exactly where does it go? If you produce not quite enough, you
can always boost the water lever by using an immersion heater for a little while or
by allowing a linked heating system to kick in slightly to top up the balance.
Using a small boiler
HORIZONTAL PLATE type boiler, will easily provide 3kw / approx 10,000btu of
heat output to either water or radiators. This is generally enough to supply 3 standard
sized radiators or a standard sized hot water tank. A thermostat and small central
heating pump should always be used when heating radiators as water can have a long
run to travel.
It is always wise to
fit an extra radiator though (eg, 4 instead of 3). If only running radiators, the heat
will be spread further and the radiators may not get quite so hot,
but at least there is a
lesser chance of overheating water if the stove is being run particularly hard.
When heating a hot
water tank only, this can be gravity fed as long as the hot water tank is above the level
of the stove. As the incoming water is heated, it then rises to the hot water tank. A
thermostat should be fitted along with an "emergency” radiator - so if the tank gets too
hot then the thermostat trips and sends the excess to the radiator.
One kilowatt per hour
(kw) of heat is approx the equivalent of a single convector radiator around 600mm
high x 1000mm wide.
Stoves are all rated to
the MAXIMUM achievable heat output. Therefore if a stove has a maximum heat
output of 10kw as an example - it is capable of producing up to 10 standard sized
radiators of heat to the room. Despite this, stoves are not generally intended to be burned
at 100% maximum.
Infact, 70% of the
maximum achievable should be saturation point. This is when the maximum amount of
produced heat is being stored in the stove, (with very little wasted heat escaping
from the chimney), gasses are being reignited and fuel being burned to optimum. If
you go outside, and look at the top of the chimney, the gasses should be running clear
and only a haze seen.
Burning at too high a
rate is wasteful of fuel, given most of the extra heat is lost up the chimney and can put
any stove at risk long term risk of stress or cracking. More than 10 > 20% below
this point, deposits are not fully burned off and gather inside the chimney forming as
tar. Looking at the chimney from outside, grey smoke can be seen.
Under general usage, if
you buy a stove with an excessively high heat rating to the room space means you
have to constantly run the stove very low. By doing this for frequent long periods
of time, far less water is produced so this practice, more deposits are formed and
chimneys and liners are at more risk or deterioration. It is therefore more
practical to often have a smaller unit with a more comfortable output of heat to the living
space and run it nearer to the top end 70% to get the most out of the boiler whilst
topping up the heat to the system if required by other means (such as immersion heater, combi
In many cases where a
50 : 50 split or wrap around type boiler stove is being fitted, the heat output to the
room will well exceed the desired water output. A way of increasing the water
output to the rads if also heating hot water could be to fit a motorised valve or
solenoid type switch. Therefore, once the hot water tank is heated and full - the water
bypasses that and on to the rads. The system can be "boosted” by switching on an
immersion heater if required. With a solenoid type switch you should be
able to manually choose to divert the water from hot water tank to
rads and back.