The popularity of condensing wall hung boilers is growing rapidly in the United States. In fact we are approaching a time when close to 50% of gas water boilers sold in the US are condensing. Condensing boilers when properly applied will run at optimal efficiency levels. The condensing boiler is part of the heating system and it works in conjunction with the rest of the system components. An important part of the heating system that may go unnoticed is the water. The water flowing throughout the system piping impacts the transfer of heating energy. Water chemistry needs to be considered when installing or servicing a condensing boiler. Poor water quality will lead to poor heat transfer, noise and loss of efficiency. Oftentimes a new installation may bring system noise that causes concern. The comment “the old boiler never made those noises” is one we are all familiar with. The noise can be very unsettling to the homeowner and can cause contractors to have concerns. The traditional cast iron boiler may have been operating with poor water conditions for a number of years without any noise; however the system was still experiencing poor heat transfer and this resulted in higher fuel costs.
BUT DON’T LOSE FAITH. Understanding the entire system and how to treat it can make all the difference.
In order to remedy new system noise it is important to understand what’s going on inside the boiler. The water is boiling inside the heat exchanger. But why? Most of us are familiar with this in cast iron products where we call it kettling; this kettling noise happens when overheating and or air builds and let’s water flash to steam. The noise is more noticeable in lower mass boilers because the boiling is rapid which results in an increased noise level. To understand why there’s a noise level increase, let’s look at the differences between the two boilers. In a cast iron boiler you have a “lazy” flame under a high-mass cast iron block, with slower heat transfer and boiling happens at a slow rate. Now imagine a blowtorch on a small cup of water. The boiling happens at a much faster rate so instead of getting a couple of pings in a heating cycle you notice an increased level of noises coming from the boiler.
I recall a job site visit in 2012 at a beautiful farmhouse in Western Connecticut. According to the homeowner, the boiler was making “whale calls.” The first thing I did when I got there was take a water sample. I spent hours running tests, combustion analysis, flow rates and so on searching for the cause of the noise all to no avail. The homeowner came down and offered me a glass of water. When I said, “No thank you” she replied, “You really should, we have the sweetest water here.”
When I took a boiler water sample the water was crystal clear, so I initially ruled out poor water quality. But then the light bulb went off, when she mentioned having the “sweetest water.” The water supply contained a high mineral content in the form of dissolved solids, which coated the heat exchanger. Without a product to clean the heat exchanger, I had to improvise. I brought the boiler up to high limit quickly. This brand of heat exchanger can withstand rapid temperature changes. Don’t try this method of cleaning without factory supervision. As I did this, black flakes started coming out of the purge hose and the boiler was immediately quieted on the next run cycle. I suggested a system cleaning product and a prevention product to keep these minerals in solution.
In essence, the minerals were cooked to the heat exchanger and caused a thin orange peel-like coating. This coating works like an insulator and decreases heat transfer causing overheating. Like an orange peel, the coating has little spaces where the water can come in direct contact with the heat exchanger. In these areas you have the extra heat from the larger insulated areas trying to get to the water, passing through a small pinpoint area. When the water comes in contact with these super-heated spots in the orange peel-like coating, the water boils. The bubbles that are created from the boiling quickly collapse in the cooler water, causing a loud banging or pinging noise. Good old’ fashioned kettling in a modern boiler.
Another way to know this happening is by watching the pressure gauge while you hear the noise. You will see the needle dance and the pressure fluctuate rapidly at a 1 to 2 PSI differential. This condition will also compromise total system efficiency. These build-ups with insulating properties can decrease heat transfer rates from your heating elements; lowering the total system efficiency. Andrew Lapinsky from Sentinel Cleaning Products is quoted as saying “System cleaning and stabilizing is the best way to ensure total system efficiency.”
With an increased understanding of what is happening in the system new condensing boilers can be used as a replacements for older cast iron boilers; without any noise concerns. Understanding water chemistry and flow allows installers can become better troubleshooters and avoid costly callbacks. Hydronic cleaning products and system stabilizers have become another tool in my toolbox. For more information on the many ways to improve system performance attend a Hydronic Boot Camp or speak to your condensing boiler manufacturer. At least that’s what “Simon Says.”