One of the more efficient ways to heat both your water and your space with the same units comes through the boiler system. Recently, the Combi-Boiler has come into popularity to compete with the traditional boiler, but which is better for your house?
- Boiler systems have been around for about 60 years
- New High Efficiency Boilers are minimum 92% efficiency and average over 95% compared with 56-70% for older Boiler systems
- Less complicated mechanical components means less mechanical problems and servicing
- Combi-Boilers have up to a 20 year lifespan
Traditional Boiler System
Let’s start with the old-school boiler system, which has been around for about 60 years with little change to the technology. The unchanging technology has allowed for a very simple design that has few parts, resulting in less mechanical problems. The down side of the simple system, however, is that it will not provide the best in-home comfort or efficiency. The boiler can only operate at 100% power or 0%, resulting in overheating and wasted gas usage. This is especially noticeable in the spring and autumn when the temperature changes drastically throughout the day. The new high-efficiency boilers have a modulating system, that can adjust the power setting of the unit to match the needs of your house to provide maximum comfort and efficiency.
The boiler does not heat your house through the traditional sense with hot air running through ducts and vents just as a furnace would. Instead, it uses in-floor radiant heating and hydronic baseboard heaters. Without air running through vents, it creates a very low-dust environment, however, it does mean that air conditioning is very expensive to install to work with the boiler.
Both of these products are becoming more common in newer houses, and use the boiler as a heat source. The boiler heats these by sending hot water through small pipes in the floor or baseboards of a house, where the heat from the water is transferred to the floor or baseboard, and then into the air of your house. Just like the water moving between the hot water indirect and the boiler, this water is non-potable and in a closed-system loop.
The efficiency of the boiler system can range greatly depending on the age of your unit, as well as the design. Older boilers only had an efficiency rating of 56 – 70%, however, newer systems are able to reach the mid-90% mark. The worst in this category is what is called a mid-efficient boiler, will run between 80 – 83%. For a system to be called a high-efficiency boiler, it must be at least 92% efficient, and the best of the bunch will top out at about 98%. Typically, the only boilers that are high-efficiency are also condensing boilers, where the combustion gases from the gas that helped to heat the water originally, are saved and also used to heat water.
To reach this high mark, a modulator is recommended. This is a device that allows the boiler to work at a reduced power level. A system without a modulator will work at full power until it reaches the desired water temperature, and then shut off completely until the water is cold enough that it must be heated again. If a modulator is installed, the boiler will work at lower power, strong enough to keep the water warm, but low enough to save more power than a non-modulating boiler.
The high efficient boilers work well with a hot water tank called an indirect. It is a fairly simple system, in which hot water from the boiler is sent through a coiled heat exchanger in the indirect unit, where it heats cold water stored in the indirect tank through heat transfer. The water moving between the boiler and the indirect heat exchanger is non-potable, meaning that it is not safe for consumption, and is in a closed-system loop, meaning that it is never used for anything else.
Combi Boiler System
As mentioned earlier, the combi-boiler system has recently come into more popularity, especially in apartments and townhouses, as it is a much smaller unit than that of the boiler and indirect. The end result of a combi is the same as the traditional boiler, it will heat both your hot water and space in the same unit. However, most units can only perform one function at a time. The Rinnai I-120 is one of the few boilers on the market that can provide both at the same time.
The combi only heats water on demand, as opposed to always keeping some warm like a boiler. When a faucet is turned on, water is sent through a coiled heat exchanger where it is heated almost instantly. Some models may have a small tank that holds some pre-heated water, although these are less efficient, as water is constantly being heated, instead only when it is needed. Just like the traditional boiler, the combi heats your space through in-floor radiant heaters, and hydronic baseboard heaters.
A 160,000 BTU combi will suffice for a three or four bedroom house, but anything larger than that you may have to upgrade to a 199,000 BTU unit. The lifespan of a combi is about 20 years as long as it is serviced regularly, but is more likely to break down or require maintenance, as there are a lot more moving parts than the traditional boiler.