Things to consider about hydronic systems
It used to be we would install a new boiler and forget about it, but those days are long gone.
Due to the narrow passages inside the boiler and circulators, the condition of the water side of the hydronic system should be considered. When replacing a hydronic boiler, consult with the equipment manufacturer and a competent water treatment professional.
The following are examples of conditions we found on some jobs where the water chemistry affected the boiler operation and life.
Sounds like a whale: This was the exact phrasing a frantic customer said, asking me to send a tech right away. This piqued my interest and I went there. When the boiler fired, it moaned loudly. I tested the Delta-T, or temperature rise, across the boiler and saw it was about 40° F higher than the manufacturer recommended, which meant the flow was insufficient. The water side of the boiler was scaled and the flow switch was frozen in place.
Chemical cleaning: A local university purchased a descaling additive for its system because the school thought it would remove the energy-consuming scale from its boilers. The scale was the only thing holding the old system together. Within a few weeks, the piping and the boilers started leaking everywhere. When starting a chemical treatment on a neglected system, I do not like to be too aggressive, as it could cause failures like this.
Snap, crackle, pop: There is a famous cereal known for its distinctive sound when milk is added to the bowl. That is the same sound you hear when a scaled boiler starts. The sound is caused by the water turning to steam inside the scale. If you hear that noise, you most likely have scale inside the boiler.
Dye or no dye?: A medical facility in my area changed water treatment vendors, and the new company suggested using pink colored dye in the treatment. The distinctive hue would let the owner know if a pipe was leaking. Shortly after the pink dye was added, a nurse filled a white Styrofoam cup with water from the stainless-steel fountain in her area. As she was about to take a drink, she saw the water was pink. She called the maintenance department and asked why the water was pink. The investigation uncovered a cross connection of the hydronic piping and the domestic water. Ever since hearing this, I have been sold on using dye inside a chemical treatment program.
Boiler construction matters: A client with an aluminum boiler developed a leak in the heat exchanger after only a couple years. The cause of the failure was because the water treatment company did not know the boiler was constructed of aluminum. On another project, a cast-iron hydronic boiler had leaks when the chemical treatment attacked the elastomer seals between the sections. Each boiler type requires its own individual type of water treatment. In addition, the metallurgy of the system distribution piping should be considered.
Always use a water meter: I have been taught the best water treatment is a tight non-leaking system. I prefer to use a water meter on every project to allow the monitoring of system water consumption. A hydronic system should have no leaks. When inside a boiler room, look for and repair water leaks.
Air removal: According to Spirotherm, water at 50° contains about 2.3% air. When the water is heated to 195°, the water contains only 0.3% air by volume. The remaining 2% of the volume is air released into the pipes, where it starts the corrosion process. For every 100 gals. of water in the system, it will release about 2 gals. of absorbed air into the system when heated. Most boiler manufacturers recommend a high-efficiency automatic air separator, such as a microbubble type, to remove the air.
pH readings: The pH should be tested on a regular basis to verify it falls within the manufacturer’s acceptable range. I like to also check the pH of the city water that fills the boiler.
Feeding the chemicals: Most water treatment chemicals for a hydronic system are introduced to the system using a sidearm feeder. I suggest using a feeder with a filter which will help remove some of the particulates from the system.
Soft water: While a water softener is common on steam systems, we are seeing more hydronic systems using a softener as well.
Filtering the water: According to ADEY Global Technical Director Neil Watson, almost 70% of circulators returned to pump manufacturers fail due to iron oxide and other water quality issues. High-efficiency filtration is being installed to capture some of the small particulates that slip through ordinary pipe strainers. Some boiler room designers also use a magnetic-type separator to capture the magnetite common in hydronic pipes. Magnetite is a byproduct of corrosion inside the piping.
One of the challenges of trapping the magnetite is because it is a fine powder. The high-efficiency electrically commuted motor circulators have powerful magnets in their rotors, which attract the magnetite. This accumulation will affect the operation of the circulator and could cause it to stop working all together.
Be aware of these and other issues, and monitor the water condition on your hydronic projects.