So far, I have been focusing exclusively on hydronic heat pumps, both air-to-water and geothermal. But I felt it was time to break the thing up a bit. This time around, I wanted to dive into some of the most common hydronic misapplications or “party fouls,” that I have seen over the years.
These are in no particular order and intended to help technicians think on their feet and come up with their own scenarios, which I hope you will share via email with me. I have made a list of hydronic installation party fouls, but I am quite sure the list could easily have been significantly longer.
Right out of the gate, I wanted to highlight the consequences of oversizing equipment. Oftentimes in the field, I will come across projects where for whatever reason the principle “bigger is better” has been carried out. That only counts with Monster Trucks and ice cream cakes. Oversizing equipment happens frequently, and typically, people will use the turndown ratio as the reason why the oversized boiler won’t hurt anything.
I quite frequently see homes that are going to get a complete hydronics package, and the boiler ends up being 115,000 btu/h with a 10:1 turndown. It is sized for the domestic load, not the heating load, which is typically smaller. The turndown on modern boilers means that when the home needs 14,000 btu/h, the boiler can modulate. And when we have domestic calls, it can ramp up and quickly charge your indirect hot water heater.
As soon as a swimming pool comes into play, we immediately see people bumping the boiler up to a 399,000 btu/h boiler. So, what’s wrong with that? Well, we immediately just made the project much more cost-prohibitive — bigger venting, bigger pumps, bigger pipes, and more expensive replacement parts.
The reality is that you don’t need anywhere near that big of a boiler, much less a second boiler to heat the pool. Remember, in the summertime, your boiler that was heating your home is now chilling in the basement and looking for a summertime hobby. Why not heat your pool with it?
In my own home, I have a pool that is roughly 25 ft. by 15 ft. and a six-ft average depth. That makes the total pool volume roughly 16,875 gallons. Lifting the water from 50 F to 70 F over a day would take 93,825 btu/h. No need for a second boiler, much less a bigger boiler.
The one that always boggles my mind is when someone thinks they don’t need glycol in the system. On two separate occasions, a contractor friend of mine ran into garage radiant floor circuits without glycol. The way that some try to get around the lack of glycol is by continuous circulation of the pumps. If there was a power outage, they would be able to quickly discover why this solution doesn’t work.
There is also a misconception that plastic pipe is safe without glycol and that it won’t fail since it can’t expand and burst in concrete. That is simply not true.
If that were the case, we would not see jobs with burst pipes in concrete. When a plastic pipe filled with fluid freezes inside, a concrete slab may not be able to expand uniformly, which will result in damage such as splitting in the plastic tubing.
Even if the concrete did have a void where the pipe can expand, you assume wrongly that the pipe cannot have an ice dam form inside it, which would build pressure to the point where the pipe will fail.
To put this one to bed, CSA B214-21, Clause 13.3, requires freeze protection in hydronic systems when installed in locations where it can freeze. The hydronic system needs to be designed around end users not understanding how the system operates. And remember that one day the homeowner may sell the house one day, and the new homeowner might not inherit this knowledge with the sale.
Utilising reset heating
One of the things I like to do when I get invited to go to a job site with a contractor is doing a few checks. The one that commonly is overlooked is the outdoor reset. I know that on some boilers, the outdoor reset can be a huge pain to set up, but as boilers get more and more advanced, it is getting much easier.
Modern condensing boilers can have their outdoor reset settings programmed quickly. Even the most novice technician will end up with a boiler that is adequately saving fuel and delivers comfort.
Without utilising outdoor reset, we forget that we are impacting comfort. The number one thing that we are supplying with our systems is indoor environmental quality, or in more simple terms, comfort. If we are pumping out 140 F water when we only need 100 F water, we will overheat spaces, which will impact comfort and reduce system efficiency.
For every 4 F, you reduce your boiler water temperature, you can expect to see savings of one per cent. This might not seem like much, but amplify that over 10 years and keep in mind the skyrocketing costs for fuel.
It is not even a matter of the cost of the reset controls at this point since most modern condensing boilers typically come with the sensor. In scenarios where you are doing a retrofit and can not get a wire to the right side of the building, there are some well-designed wireless sensors in the market.
Piping a heat pump like it’s a boiler is another common installation mistake seen in the industry. Oftentimes where we go wrong is with the application of the math for sizing piping on a heat pump. I went into more detail about this in a previous article (Heat Pumps are not Boilers in September 2022 issue).
Let’s take a 60,000 btu/h boiler. To size the tubing, we first need to figure out the flow rates using a typical Delta T of 20 degrees. By doing this, we get 60,000 / (500×20), which equates to six GPM. This fits almost perfectly with a 3/4-inch copper piping at 3.94 ft. per second.
Where things go wrong with a hydronic heat pump is mistakenly assuming that you can achieve a 20-degree Delta T. Many hydronic heat pumps can only lift the water five to eight degrees. If we redo that formula for a hydronic heat pump, 60,000 / (500×8) = 15 GPM.
If we try to feed 15 GPM through a 3/4-inch piece of copper, we have a flow velocity of 9.83 ft. per second, which is far exceeding the flow velocity suggested for the copper pipe on a hydronic system.
Best of all, you have inadvertently put a choke point into your system, which in many cases results in catastrophic equipment failure. Many times a year, I am forced to condemn a hydronic heat pump system that has been piped this way.
A lot of manufacturers will publish their flow rates in their manuals, so I’d suggest referring back when need be.
I can tell you that just about every item listed here has happened to me firsthand, and in some cases from doing them myself. Together as an industry, we need to recognize our strengths, work on our weaknesses, and collaborate to positively grow the industry.
There are so many talented designers and installers reading this article, and I would love to see you engaged and involved, not only just in installations, but in guiding training and the future of our industry. We will go into some more party fouls in Part 2.