Heat Measurement – kW,s Explained

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What’s a Watt? What’s it Matter?

Now that it’s getting chillier, you’re probably deciding on the best way to keep warm in the coming winter months.

Remember that in addition to simply pumping heat into a living space, effective heating relies on removing the moisture which has built up in the house, and maintaining an even temperature throughout, which will continue to drive out the damp – the cause of interior condensation, mildew, and winter ills and chills!

Bear in mind that the average home requires 16 kW to achieve this objective. Now that’s where heating becomes technical!

Just what is a kilowatt??

Really, you don’t need to know , if you understand that most electric heaters produce 2 kW – and as we all know, that’s barely enough to heat one room let alone a whole house! So if you used electric heaters to provide your comfort, you’d need about 8 to 10 appliances!

Unflued gas heaters have a similar output to electric appliances, so you’d need a similar number. But they also produce water vapour, so moisture levels are kept high.

Forget about your open fireplace if you’re looking for a comfortable winter. Not only is it dirty, but as almost all the heat goes up the chimney, you’re sitting in a draught, constantly refuelling a fuel guzzler which is less than 10% efficient.

Let’s look at high tech-wood heaters. These have a large heating capacity – generally between 12 – 20 kW, so have the ability to effectively heat the smaller and larger home, as well as everything in between. What’s more the heat spreads evenly through out.

The real secret to wood heating is the way heat is transfered into the living area.

Radiant heaters, which are generally free standing, are normall cheapest to buy because they don’t need sophisticated convection air- ways. Beams of heat are dissipated from the sides of the firebox and from the fire, through the glass door if one is fitted. The radiant heater is ideal for heating large open spaces or areas with high ceilings as the radiant heat will heat objects in its path, rather than the air.

Radiant-convector heaters combine the advantages of radiant heat with warm air convection, and they come as either free standing or inbuilt models. While objects within the immediate room are heated quickly, these appliances quicky set up warm air convection currents within the entire home, and moving colder air back to the heating appliance for continuous heating.

Radiant-convectors are ideal for areas which are divided off by door and walls and which have a standard type ceiling.

Irrespective of which appliance though, for efficient burning it is important to use dry or “seasoned fuel”, otherwise useful heat will be used driving off excess moisture from the wood.

Softwood has large cells, and takes less time to to season than hardwood with its more compact structure. While softwoods such as pine can be ready for use in 6-12 months hardwood can take 1 – 2 years to dry to an acceptable level. Yet weight for weight they have about the same heat content.

It’s also beneficial to understand how a slow combustion wood heater works. Most heaters these days incorporate a double burning system which enhances heat transfer and reduces emissions, so that the appliance will comply with internationally set standards.

And it’s this double burning which sets today’s wood heaters apart from older solid fuel heaters.

As wood burns it passes through several stages of decomposition.
Firstly as the temperature rises, the outer fibre chars, and starts to burn. The cellular structure breaks down releasing the energy rich gases it contains. More fibre starts to burn along with some of the gases. But the gases can’t burn completely because the temperature within the firebox isn’t high enough, and they are particularly difficult to ignite.

That’s where the “secondary chamber” at the top of the firebox comes in. As the fire settles, the flames heat the underside of this chamber. The temperature is elevated to a point where, with the addition of a little extra air, igntion occurs when the residual “smoke” from the fire passes through.

It’s this process which results in combustion efficiencies of over 90%. This means that the maximum amount of heat is available to use in your home as winter wamth.

But you can save even more than just heating costs. With a wetback fitted, household water heating bills can be slashed through out the year, and hot water will constantly be available, even when ripple-controlled electricity is in force.

And what about pollution? The environment impact of wood heating is sometimes questioned. But you can rest easy. All appliances now sold here and in Australia conform to an international standard which not only sets maximum permissable emissions levels but also minimum efficiency standards.

The emissions levels are so low, that the environmental impact is insignificant. Further burning wood is no more detrimental to the environment than leaving it to rot on the forest floor, as the carbon dioxide levels are the same for both processes.

So there can be no doubt that wood heating is perhaps the most economical, efficient and environmentally sound heating option to heat your home and to keep everyone as warm as toast right through winter.

For further information about the benefits of wood heating, contact your nearest member of the N.Z. Home Heating Association- (The Fireplace Technician)

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