Hydronics 101, Barba-style


When Eric and John asked me to write a blog post on “Hydronics 101,” I have to admit I was a bit overwhelmed. Where on earth do you start? There’s boiler piping, pipe sizing, circulator selection, heat emitter selection, controls wiring, and so on.

There are so many avenues to take when it comes to “Hydronics 101” that choosing a starting point becomes quite a daunting task.

But then I thought of one of the very first training classes I ever did.

It was 1995 during a full-day program on radiant floor heating. We were going through the process of radiant design — figuring out installation method, tube spacing and water temperature. We were looking over charts and graphs to make heads or tails out of this radiant job when a fellow in the back of the room raised his hand.

“Don’t you have computer software that figures all this stuff out?”

Yep, we do.

“Then why are you wasting our time telling us all this? Just give us the software and we can go home.”

Ummm, it doesn’t quite work that way.

Design software, whether it’s for hydronics or forced air, is really nothing more than a fancy calculator. It does the arithmetic for you, and that’s about it. It doesn’t think for you, it doesn’t make decisions for you and it doesn’t tell you if you’ve input the wrong data.

It’s a calculator.

That’s it.

I like to ask folks in my classes how many of them have been formally trained in how to perform heat loss calculations. We call it “doing the math.”

As the years have gone by, fewer and fewer people raise their hands. No one’s teaching heat loss anymore, and I think it’s a shame. Knowing the actual heating load of a house or of a zone is the real “starting point” for beginning hydronics or for advanced hydronics.

How can you size a boiler if you don’t know the load? You can guess, but it’s just that: a guess. You can base your load on a standard BTU-per-square-foot multiplier, but that’s not a heat loss calculation. That’s just a guess with better PR. You can even measure the radiation, multiply by whatever multiplier you care to use and call that the load. But all that tells you is how much radiation is installed.

Good to know, but it doesn’t tell you the actual load of the house.

There’s no way around it: a good old-fashioned heat loss calculation is the only way of getting anywhere close to what the actual load of the house really is. Are “by-the-book” heat loss calculations 100% accurate? Nope — there’s so much fudge built in to the calculation methods out there that it’s a wonder we’re not all diabetic. But they’re still better than guessing.

During one of Taco’s Heat Loss classes a while back, the class was presented with a set of blueprints for normal, stick-framed house. There was nothing special about this house. It wasn’t super-insulated with super-low E windows or anything. It was a basic 2200 square foot ranch, with an outdoor design temperature of 7 degrees above Zero.

I asked the group, based on their years of knowledge and experience, to come up with their best, most accurate estimate for the heating load of the house. Their responses ranged anywhere from 55,000 BTUH on the low end to 125,000 BTUH on the high end.

The class then worked through an I-B-R based heat-loss analysis using the H-22 Heat Loss Design Guide (find it on Amazon under “Freaking Awesome Heat Loss Book!”). Using charts, graphs and real live, honest-to-goodness math, the class calculated the heat loss of that house to be a whopping 31,000 BTUH.

Well ain’t that a kick in the head!

Bottom line gang: any fundamentally sound hydronics system starts with the math. Heat load allows us to size our boiler and all of our piping as accurately as possible, which can have a major impact on materials costs. And only when we know the heating load and the size and length of the pipe that heat has to go through can we figure out what we need for a circulator, because load determines flow and pipe size and length determine head loss.

And weather impacts it all.

From there we can look at all the different types of circulators (steep curve, flat curve, single-speed, 3-speed, variable speed, Delta-T, Delta-P) and try to determine which one best fits the job we’re looking at – and no, there’s NO SUCH THING as “the only circulator you’ll ever need.” That’s a load of hogwash.

So where does “Hydronics 101” start? It must start with an accurate idea of what you’re trying to accomplish, which is to make sure this structure heats on what’s commonly referred to as “the coldest day of the year.” Now, if you’re simply replacing a dead circulator, there’s precious little math that needs to be done (but you still have to know about circulators and their impact on systems – that’s a future segment). But if you’re replacing a boiler or actually starting from scratch, the only right way to start is with a pad of paper, a scaled ruler, a pencil and a calculator. If John and Eric invite me back, we’ll walk through simple heat loss calculations done the old fashioned way. Software will do it quicker, but in order for software to be a tool and not a convenience item, it’s important to know why it came up with the numbers that it did.

As my old man used to say, “Knowing how is good, but know why is better. Because those who know ‘how’ will always work for those who know ‘why.’”

292064_165510476919119_1119696213_n copyJohn Barba is training manager for Taco Inc.



6 thoughts on “Hydronics 101, Barba-style

  1. Great article as usual! I’d be curious how many contractors from that class went home and started installing properly sized boilers? Based on the number of sub 100K boilers I see,I’m guessing not very many! If I had to pick a musical accompaniment for this one, I’d go with Lyin’ Eyes by The Eagles! 🙂

  2. Thank you John…again…As I’ve mentioned in some other discussions knowing what the system requires is only possible through a detailed heat loss. Customers that insist on a “budget” number will get just that a “budget / guess” quote with provisions made for performing the heat loss upon deposit. Modulating boilers offers some forgiveness to get us in the door. Although a new system is never installed without signing off on the “heat loss”…

  3. John you are right on as usual except half of one point. I teach about heat loss in almost every seminar I do. I spend about 1/2 hour each time on the importance of proper sizing, not actually on how. I wish I had a dollar for every time some said that since high efficiency boilers modulate so it is not as important. Wrong!!! We want the boiler to modulate low enough to meet the smaller loads also.
    Another problem is too many zones. With high efficiency boilers I would rather see larger zones and longer run times.
    Keep up the good work John.

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