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Let’s Talk About Piping Size

In life, we look at objects and try and determine what the size can tell us: how big is it or how small. We use these observations to increase our knowledge of the object we are looking at. Being a hydronic contractor, everything is about what size fits the need at hand and the mechanics being used to provide solutions and solve problems. When we deal with boilers, piping and pumps how big or small really make all the difference. Not remembering that “Size Matters” can severely impact the quality of installations contractors perform.

We get a phone call from a property owner I do a good amount of work for. He is having a hot water issues at an apartment complex I have never seen nor done work in before. He asks if I can look at this newly installed water heater because they were getting lots of resident complaints about running out of hot water in the mornings and evening hours. Tenants were posting the complaints all over social media to make matters worse. Frustration and anger can spread quickly.

This site houses a twenty-eight unit, single-bath, garden apartments. The owner, maintenance manager and installing contractor will be all be meeting me on site. This kind of turn out on a job site always make the day go faster. We review the newly installed (allegedly defective) indirect water heater. The on-site contractor is more than happy to show me the way to the boiler room where the “defective” indirect water heater is installed. The first thing I notice is that the install manuals are neatly tucked in their plastic pouches on the side of the water heater. This started the gears turning in my own head that this might be an issue of lack of research and knowledge about the equipment at hand.

The room consists of two, older 80% cast iron gas boilers with about 850K gross input, and a shiny new 119-gallon IDHWH. It was time to get down to business and find the problem. After a quick glance, I see the pipping from the boilers is 1-1/2” copper and was quickly reduced to 1” over to the indirect, on the supply side. Then the piping around back of unit against the wall the return is 1” with a Taco 007 pump. I now realize this isn’t a defect issue, but a size issue.

I ask the contractor, “Why did you reduce to the pipe size?”

“Well that’s the pipe size on the indirect.”

It would seem to be that the contractor observed the unit and the piping size that existed and stopped right there.

I followed up, “Why did you use a 007 pump?

“That’s what the supply house sold me.” piping size

This once again is an extremely common response throughout my career. I grab from that pristine book, in all its glory, and flip to the ratings and specifications page. The recommended flow rate is 14 GPM. The contractor explains that a 007 model will do the required 14 GPM. Now I go back to the trusty manual. Soon enough, I show him that the pressure drop of heat exchanger is 14-ft of head. I pull up a Taco 007 pump curve on my smartphone, go to 14 feet of head and the calculation says the pump can do zero with that much head pressure.

The contractor’s eyes widened a bit and I could see him rethink the entire process of how the room was laid out. It was as simple as looking at the math and the sizes needed to make the equipment operate at its intended function and quality. I could do all this with the best tools ever: knowledge.

In the end, we wound up replacing the complete boiler room fully equipped with mod-con boilers and a forty-eight-gallon instantaneous indirect water heater. That’s a story for another time.


For more information, check out an article we published describing Best Boiler Maintenance Practices


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