The path to maximum wall hung boiler efficiency.
by Joseph Peretti
It's no secret that gas-fired wall-hung boilers will not just be a passing fad in the hydronic heating industry. They will, in fact, be the driving force in the hydronic heating industry for the foreseeable future. However, they are only half the equation. To truly maximize the efficiency of the entire system, we have to look at the system in regards to heat emitters.
As the heat source, gas fired wall hung boilers boast:
- 90% thermal efficiency
- Offer weather responsive reset control
- Multiple turn-down ratios
- Are easy to install
- And they qualify for many rebates
These boilers, rated at 90% efficiency, are usually installed complete with primary/secondary piping, smart circulators featuring modulating ECM motors, and sit proudly on a beautiful painted "wall of heat.” Yet sadly, they’re usually connected to fin-tubed baseboard heat emitters or fan coils which, by the nature of their design, cannot deliver the adequate amount of BTUs needed at low-supply water temps during the "shoulder seasons" that allow the boiler to condense and run at 90% efficiency. The boiler must now be adjusted to deliver higher water temps to maintain comfort which now diminishes boiler efficiency, sometimes well below 90%.
It's ironic that low-mass wall-hung boilers are at their best connected to high-mass heating systems. In this scenario, wall-hung boilers do not really function like boilers as we know them. In their purest form, connected to the properly designed systems, they perform as BTU injection devices delivering water to higher mass heat emitters at lower water temps.
Panel radiators provide probably the best path to maximizing overall boiler efficiency. They’re not only high mass-heat emitters that deliver substantial BTU's at very low supply temperatures. They’re also:
- Made of steel and are painted with high-quality paint
- Reasonably priced
- Attractive, stylish, and in some cases, customizable
- Lend themselves to individual zoning
- Perfect for "shoulder seasons" or the times of year during a heating season when we experience warmer days and nights and our homes do not require as many BTU's to keep the dwelling at a comfortable temperature.
It's during these "shoulder days" of a heating season that energy dollars can be saved, and they account for 40%-60% of a boilers total run time over the course of an entire heating season. It's a proven fact that for every 3 degrees you can lower your boiler's supply water temps you will save 1% annual fuel efficiency or AFUE.
In other words, if you can heat your home with water temps 30 degrees cooler utilizing a weather-responsive wall-hung boiler working in conjunction with a properly-sized panel radiator system you can be saving 10% to 15% in fuel dollars compared to your neighbor using the same boiler connected to a HWBB system. You’d be saving substantial energy dollars!
There is much more to consider here and while not every person in every home can achieve it, annual fuel savings of 30% or more is the expectation of a properly designed and installed system as I’ve describe here. This is no joke or pie-in-the-sky claim. But it’s important to note that during the coldest days of the year, no one's boiler, regardless of manufacturer or system to which it may be connected, is running at its highest efficiency.
In my next article we will take a "deeper dive" in to the panel radiator world and examine sizing, piping strategies, and zoning.
To learn more, please feel free to contact myself, your TGG sales representative or your Granite Group Fuel Market Manager.