Comparison of convection and condensing gas boilers

For effective heating and comfort in your house, selecting the ideal boiler is crucial. Convection and condensing boilers are the two most common types of gas boilers. You can choose your home heating system wisely if you know the differences between the two types; each has advantages and disadvantages.

Many homes have traditionally opted for convection boilers due to their dependability and ease of use. They function by heating water in a storage tank and then using pipes and radiators to distribute the hot water throughout the house. These boilers are a popular option for homeowners on a tight budget because they typically cost less to install than condensing boilers.

Condensing boilers, on the other hand, are renowned for their excellent energy efficiency. The purpose of these boilers is to recover heat from the flue gases that traditional boilers would otherwise waste. Condensing boilers can achieve efficiency levels of over 90% by capturing and condensing the water vapor in the flue gases, which significantly lowers energy costs and carbon emissions.

There are some significant distinctions between convection and condensing boilers that you should take into account, even though they can both heat your home efficiently. To assist you in selecting the ideal choice for your house, we will compare the efficiency, cost, installation, and environmental impact of convection and condensing gas boilers in this post.

Coefficient of efficiency of boilers – what, how and why

Manufacturers of gas heating equipment indicate different values of the coefficient of performance (COP) of their products, and often this parameter exceeds 100%, which is impossible because of the law of conservation of energy. To properly navigate these data, it is necessary to look into history and trace the path from the primitive fire to the modern gas boiler. At first, people burned fires in caves, there were a lot of forests around, so it did not even occur to anyone to evaluate the efficiency of this method of heating. After a while, someone noticed that a fire built in a hearth made of stones warmed better than a fire burning on the floor of a cave.

The first ugly hearths were gradually replaced by "black-style" stoves made of stone and mud brick. They were nearly ten times more effective than a typical fire, but because they formed carbon monoxide and carbon dioxide-filled zones in the room, they posed a threat to human life. With time, gray and white stoves took the place of black stoves; that is, the smoke from these stoves was expelled through a chimney as opposed to a tiny window shower. After a while, these once-ideal stoves were superseded by models with extra heating panels, which had a notably higher efficiency.

Boilers replaced stoves, but not because they used less fuel; rather, they did so because they were small and could heat multiple rooms with a single unit. Every new boiler generation or type had higher efficiency than the one before it at the same time. Initially, wood and coal were used to fuel boilers; however, due to their high cost, these designs are difficult to automate, and the cost of fuel for liquid-fuel appliances makes them uncompetitive with other types of devices.

From inefficient gas combustion to the incapacity to extract more than half of the thermal energy from the flame, gas heating and hot water boilers were introduced at the start of the XXX century, and their technical qualities left much to be desired. However, the products had to be sold, which meant persuading prospective customers that this specific product—gas boilers in this case—was clearly superior to analogs of other types in some regards.

The first distinction was the option for automatic temperature control, but as the market grew, new models had to contend with competition from both gas equivalents and solid fuels like coal or wood. Here, marketers devised a clever marketing ploy: they started contrasting the "efficiency" of some boilers with similar parameter apparatus from competing manufacturers.

Calculation methodology

Gas boiler efficiency can be determined in a number of ways, but they are all dependent on the difference between the amount of heat that is allocated and the amount that is consumed.

This is comparable:

• gas consumption;
• smoke temperature at the chimney outlet;
• The temperature of the water in the boiler;
• water temperature in the return pipe.

Then, all of these data are linked to a "perfect boiler," whose efficiency is 100%, and which is used in advertisements and heating device documentation to show the outcome attained. More audacious people report an efficiency of 90–98%, while more modest people are content with 75–85%. All of these statistics, however, are predicated on the efficiency of a perfect boiler of the same kind.

As an example of such manipulation can be given the operation of a gas torch (autogen) in the mode of metal cutting. First, only the burning mixture of propane/acetylene and oxygen releases heat, so we can take the ratio of gas consumption to heat release as 100%. Then blowdown oxygen is supplied and, with the same supply of combustible gas the heat release increases dramatically, i.e. the efficiency exceeds 100%. If we take as a reference point the heat generation during the supply of blown oxygen, the efficiency in the heating mode will be much lower and is unlikely to reach even the 50% mark. Therefore, in order to increase sales of the product indicate the most favorable data, omitting about the point of reference.

Real efficiency of gas boilers

It’s important to mentally picture an ideal unit with no losses in order to assess the true efficiency of gas boilers. What losses are these?

• incomplete combustion of fuel;
• excessive air intake;
• incomplete heat extraction from fire and flue gas flow;
• insufficient thermal conductivity of the metal register;
• excessive thermal conductivity of the coolant (water or antifreeze) and the material from which the water pipes are made both inside the boiler and the whole heating system.

All boilers have incomplete combustion as their primary issue. Ultimately, creating a homogenous mixture with the ideal gas to air ratio would necessitate a massive tank, numerous vortexes, and other equipment. When there is not enough air present, the gas releases less heat energy than it could and the remaining energy is converted to carbon monoxide and soot. Excess air causes combustion to occur at a lower temperature once more, but hardly any soot or carbon monoxide is produced. Manufacturers are thus compelled to set up their machinery to run in overpressure mode, even if this results in a loss of heat generation.

Heat is extracted from the flue gas stream primarily through the register, which is a multilayer grate that allows coolant to circulate inside. In theory, it is feasible to extract nearly all of the heat, in which case the smoke temperature at the outlet will be five to ten degrees higher than the coolant temperature (the losses resulting from inadequate and excessive thermal conductivity). However, because of temperature variations, condensate formation cannot be avoided in this mode. More was done in condensing boilers, where the coolant originating from the return pipe was heated using the heat energy of the settling condensate.

This allowed to reduce the smoke temperature to the return temperature plus 5-10 degrees. In an ideal boiler, the temperature of the smoke at the outlet is equal to the temperature of the air outside. As a result, the real efficiency of an ordinary gas boiler does not exceed 50% of the same parameter of an ideal water heater, but, such information will only scare away potential buyers, because no one will not want to buy a boiler with the efficiency of a brick oven of Napoleon times. Therefore, further we will give those efficiency data, which are indicated by the manufacturer, and you proceed from the fact that all of them should be divided approximately in half.

Gas convection boilers: what it is and what is the principle of their work

Boilers with gas convection heating are a classic example of a simple design. The coolant circulates throughout the heating system and produces heat as the gas burner burns gas to heat the heat exchanger above it. Actually, they’re just regular, straightforward, well-known gas boilers. They can have an open or closed combustion chamber, be single or double-circuit, and be wall-mounted or floor-standing.

The efficiency limit of this design is its primary drawback. The majority of contemporary convection boilers are between 88 and 92% efficient, and models with the highest efficiency, between 93 and 94.5%, are not always financially justified because, for a mere 2% increase in efficiency, their cost is 1.5–2 times higher and their design is far more complex. However, a significant portion of the heat from the combustion chamber escapes through the chimney and is not used, even with such high values for convection boilers. Flue gases frequently reach temperatures of 70–80–90°C.

Condensation in the chimney is another unanticipated but common drawback during operation that is not well known prior to purchase. Typically, it forms during low-temperature heating mode, specifically when the exhaust gases passing through the chimney have a temperature below 50–60°C. This is particularly true if the gas outlet is through a conventional vertical chimney, the design of which frequently permits deviations from the SNiP.

In this instance, condensate formation refers not only to a liquid but to a combination of strong acids that shorten the chimney’s and the boiler heat exchanger’s lives (assuming it penetrates it).

Regardless of the heating mode, ice frequently forms on the coaxial chimney at street temperatures below -15 °C. This narrows or blocks the combustion product outlet, causing the boiler to shut off, and the automation to trigger the corresponding error.

Other than that, the design is very sensible, straightforward, and most importantly, reasonably priced. Convection gas boilers range in price from 14,000 to 15,000 rubles for the most basic domestic floor models. The most popular models and the best in terms of "price-quality" ratio come in a range of 25–32 thousand rubles.

Advantages and disadvantages

The boiler you choose for your home is very important when it comes to heating. Convection and condensing gas boilers are two common choices that will be compared in this article. While condensing boilers are becoming more and more popular because of their higher efficiency and lower energy costs, convection boilers have been around for a while and are renowned for their dependability. We’ll explain the distinctions between these two kinds of boilers so you can choose the right one for your heating requirements at home.

Differences between condensing gas boilers and convection boilers

The only way that condensing gas boilers vary from convection boilers is in the more intricate heat accumulation principle.

Condensing models feature one extra heat exchanger in addition to the same design. The combustion products follow a longer exhaust path after combustion and cool down to the dew point. Condensate is created, which collects on the extra heat exchanger and provides it with previously unutilized heat energy by circulating coolant through it. Thus, the term "condensing" refers to the process of gathering the heat from the condensate of flue gases.

As a result, the flue gas temperature is nearly identical to the ambient temperature (which is typically between 25 and 40°C compared to 60 to 90°C for convection models). Condensing models typically have an efficiency of 103–115%, meaning that on average, they use 15–25% less gas. Conventional gas boilers have an efficiency range of 80-85% for convection and 92-98% for condensing if the indicators of both convection and condensing are recalculated using the highest heat of combustion (including the heat of condensing water vapor) rather than the lowest, as is customary. This represents a significant advantage.

All of the variations, requirements for selection, and operational quirks of condensing gas boilers

Because there is less of a temperature differential between the exhaust gases and the atmosphere, condensate does not form on the chimney headband in condensing models, which have more environmentally friendly exhaust. Every model has a coaxial chimney and a closed combustion chamber, which means less space is needed and installation is easier. However, the most affordable models, like the Protherm Lynx MKV or BAXI Duo-tec Compact, cost from 50,000 rubles, while condensationniki are two to three times more expensive.

The requirement for condensate drainage is yet another noteworthy drawback. This is a strong acid, not just a neutral liquid, as was previously mentioned, and it needs to be properly disposed of. The acid must first be diluted in a ratio of 10:1, or better yet, 25:1, as it cannot be drained straight into the sewer system.

Condensate needs to be neutralized before being emptied into a septic tank. A local treatment station, which is a plastic tank filled with neutralizing fillers, can assist with this process. Owner reviews state that during a day of operation, a boiler with an 18–24 kW capacity forms 25–40 liters of condensate.

For homeowners, selecting between a convection and a condensing gas boiler can be a big choice. Making an informed decision requires an understanding of the advantages and disadvantages that each type of boiler has to offer.

Although less efficient than condensing boilers, convection gas boilers are frequently less expensive up front. They can reliably heat your home and are compatible with older heating systems. On the other hand, they are typically less energy efficient, which results in longer-term energy costs.

Condensing gas boilers, on the other hand, extract heat from flue gases that would otherwise be wasted, making them more energy efficient. Even though they might cost more up front, their increased efficiency can result in substantial cost savings over time, making them a more cost-effective option overall.

The choice between a convection and condensing gas boiler ultimately comes down to your long-term energy savings objectives, your heating system’s age, and your budget. Making the best decision for your house and budget can be aided by speaking with a licensed heating specialist.

Video on the topic

Gas boiler traditional (convection) VS condensing

Differences between the condensing boiler and convection boiler

Condensing or conventional (convection) boiler – how to choose? BOSCH GAZ 6000 and BOSCH CONDENS 2500

Gas or condensing boiler: what is BETTER? / Principle of operation CONDENSATION boiler

Condensing or conventional boiler? Which boiler to choose for the house?

Condensing gas boiler. The bitter truth about saving money!