What Is A Condensing Boiler?

Condensing boilers are high-efficiency oil or gas-based boilers. Conventional and mid-efficiency boilers have an AFUE of 60% and 80-85%, respectively. AFUE stands for Annual Fuel Utilization Efficiency – it tells you how much fuel is turned into usable heat for your building.


The high-efficiency condensing boiler, on the other hand, can have an AFUE of 90-98%, meaning almost all of the fuel burned is turned into useful heat for your building. Why are condensing boilers so efficient? Should you install one? What are some of the myths surrounding condensing boilers? We’re going to cover all that – and more – right here. 

How Do Condensing Boilers Work?

When boilers burn natural gas or oil, water and carbon dioxide are created. The water that’s created is water vapour – essentially, steam. In a conventional boiler, that water vapour and carbon dioxide exit through your chimney. The gases and vapours that leave through the chimney in this way are extremely hot – usually around 250°C. 


There is heat trapped in that water vapour – known as the latent heat of vapourization. Condensing boilers reclaim that heat and use it to heat your building. 


Traditional boilers have only one heat exchanger – essentially, metal plates that are heated by combusted natural gas. Combustion boilers, on the other hand, have two heat exchangers. One of these exchangers is located above the primary heat exchanger – it’s cool enough that the water vapour inside of flue gases (the gases that leave through your chimney) condense when they touch it. That releases heat, which the heat exchanger uses to warm the water that will go on to heat your building. 


The resulting condensed water then drips safely into a drain that takes it safely outside of your building. 

Why Should I Install a Condensing Boiler?

If you’re looking for one of the most efficient ways of heating your building, condensing boilers are the way to go.


Manitoba Hydro estimates that you can lower your heating costs by 35% by using a high-efficiency condensing boiler instead of a conventional boiler. That’s a dramatic reduction to your monthly heating bills, and it means that condensing boilers can quickly pay for themselves.


Condensing boilers are also a green solution when compared to conventional boilers. Higher AFUE means less fuel goes to waste – and that means you’re lowering your carbon emissions. High-efficiency boilers heat your building as well as conventional boilers, so you’re saving money and being sustainable, all without sacrificing comfort. 


Are Combi-Boilers & Condensing Boilers the Same?

Combi-boilers and condensing boilers are kind of in a square/rectangle relationship. Almost all modern combi-boilers are condensing boilers, but not all condensing boilers are combi-boilers. 


You see, combi-boilers are specifically a combination of a boiler and a water heater. In other words, combi-boilers heat water both to heat your building and to provide hot water for your building. This is the most efficient way of providing both hot water and heat to your building, and it’s made even more efficient now that almost all combi-boilers are condensing boilers.


Condensing boilers, however, aren’t necessarily combi-boilers. You can have a condensing boiler that doesn’t provide hot water to your building. A fairly simple distinction, but one that’s worth talking about. 

Are There Disadvantages to Condensing Boilers?

The main disadvantage to condensing boilers? The upfront cost. Condensing boilers are more complex than conventional boilers. As a result, they’re more expensive. 


These expenses, however, can often be recouped fairly quickly. The Government of Canada and the Government of Manitoba sometimes offer rebates for purchasing high-efficiency heating units. Additionally, you can save up to 35% on your heating bills – and those savings do add up quickly.


There are a number of myths surrounding condensing boilers – and most of them revolve around misunderstandings. 


Back in the day, condensing boilers had shorter lifespans than their conventional counterparts. The water that results from the condensing process is acidic. Early condensing boilers didn’t manage the wastewater effectively, which led to corrosion. Today, however, manufacturers have mastered the art of neutralizing acidic water. The lifespans of modern condensing boilers are about as long as conventional boilers.


Another myth is that condensing boilers can’t replace conventional boilers. This isn’t true. The only real change is the need for a drainpipe through which the condensate can flow. These are relatively easy to install. Your existing radiators and plumbing can be used for your condensing boiler.

How To Optimize Your Condensing Boiler’s Efficiency

At the top, we mentioned that the gases that leave your chimney from a conventional boiler are quite hot – usually around 250°C. The gases that leave from a properly functioning condensing boiler will be 55°C.


That’s because the dew point of natural gas fumes is 55°C. In other words, the flue gas needs to cool to 55°C before water vapour condenses.


This means that condensing boilers need to heat water to a lower temperature than conventional boilers in order to achieve maximum efficiency. You see, your boiler is a closed system, through which water or steam flows, then returns. In a condensing boiler, the return water first passes through the condensing heat exchanger. The water needs to be cool enough so that the flue gases reach their dew point – from there, the water can absorb the heat energy that results from water vapour condensing.


What temperature should your water be, then? Generally, the answer is 70°C – the temperature of return water tends to be around 20°C lower than it was when it left. 


Of course, how much cooler return water will be depends on how many radiators in your building are on full blast and other factors. The very best way to ensure efficiency is by purchasing smart thermostats that can tell you what the temperature of your return water is and adjust accordingly.


Condensing boilers are the best boilers available on the market today. They offer substantial savings on your monthly heating bill, they’re more eco-friendly, and they’re durable. Looking for a reliable appliance for Winnipeg heating? Condensing boilers are the way to go.