New boilers are a lot more efficient than older models. In USA, their efficiency is now at least 82%, and some models have AFUEs (energy coefficients) above 95%, that is, they only waste 5% or less of the fuel's energy. That’s a significant energy improvement, compared to older boilers, with AFUEs around 70% or lower.
On the other hand, they are a lot more expensive; and this raises the question: do new high-efficient boilers worth the money?
Mid and high-Efficient modern boilers
It’s common to divide modern boilers into two groups: the 1) mid-efficient and the 2) high-efficient boilers; or the 1) regular and the 2) condensing boilers. The AFUE (Annual Fuel Usage Efficiency) is a rating coefficient for boilers and furnaces. This percentage expresses how much fuel the boilers or the furnaces convert into heat: say, 90% or 80%. In other words, a boiler with an AFUE of 80% wastes 20% of the fuel it uses, and it is a low-mid energy-efficient unit.
New mid-efficiency boilers have an energy coefficient between 82% and 90% (USA) and involve a tested technology. If you intend to buy a boiler of this category, look for a model with an AFUE as close to 90% as possible.
Most of the boilers being sold in the North American market belong to this mid-efficiency category, but all the new UK boilers (typically of the wall-hung type) are required by law to be of condensing type (90%+ boilers).
Most new boilers – namely condensing boilers – are sealed-combustion units. They draw the combustion air from outside, and vent exhaust gases to the outdoors through dedicated pipes.
That’s important for efficiency and safety and energy improvements. Combustion boilers emit pollutants, that should be drawn to the outside. It’s our lives and health that are at stake.Non-sealed combustion boilers emit dangerous pollutants in their burning; you should have a CO detector in each level of your house. It’s cheap (less than $30) and easy to install. See Amazon CO Detectors, for customer reviews.
Types of boilers
The condensing technology has improved steadily in the last years. But when we talk of "boilers" we should take into consideration their type.
European boilers (wall-hung boilers) are rather different from the sectional, steel fire-tube and copper-water tube American boilers, and are a lot less expensive.
The UK “combi” (from combination) boilers are basically a wall-hung water heater, able to provide both hot water for domestic uses and for space heating; they are the most common type of boiler in the UK residential market.
Typical combi boilers have a relatively small capacity, and are designed for relatively small loads, but Europeans use also “system boilers”, with a hot water storage tank, able to provide larger amounts of hot water.
Are new boilers worthwhile?
As mentioned above, the problem with new energy-efficient and condensing-type boilers in North America, is that they are a lot more expensive than regular boilers. In other words: for small or average water-heating needs they may be too expensive and their payback too long.
What's the best option, then?
The short answer is: American-type boilers do not respond well to the lower hot-water requirements of very energy-efficient homes, designed, insulated and sealed to have low space heating requirements. They can be a good choice for large homes and other buildings, with high space heating requirements, but not for very energy-efficient single-family homes.
That's a downside that you should consider when planning a new home and its heating system, even in cold climates with higher heating requirements. Consider other space heating alternatives, depending on your climate and your air-conditioning needs. Obviously, European-style condensing boilers, able to respond to smaller requirements, is among the alternatives.