So you think you know radiant?
Common misconceptions about radiant heating and cooling systems.
I talk to people on a daily basis about radiant heating and radiant cooling systems. Many people have a fairly good grasp on the basics of radiant. Some even think if you load up a joist bay with as much tubing as you can stuff in, it will work. Maybe yes, maybe no. Having been in the consulting business prior to taking my position with the Radiant Professionals Alliance, I saw many jobs where the physical plant and the distribution systems didn’t have parity. Think of it as driving a tack with a sledge hammer, or driving a railroad spike with a tack hammer. In either case, there will be problems. I’d like to go over some of these problems, expand your horizons, increase your knowledge and teach you to become a recognized expert in your field.
Heat loss calculation, what’s a heat loss calculation? It is a well-known fact radiant floors have a limitation of 30 Btu per sq. ft. per hr. output capacity. So it reasons, if that is the limit, then the easy thing to do would be to take the square footage of the building we are putting the tubing into and multiply it by 30, which tells us how big the boiler needs to be — nothing could be further from the truth.
By code (where properly applied and enforced) you are required to provide an accepted method of proving the heating and cooling needs of a given structure. Using rules of thumb will end up with significantly oversized, terribly inefficient systems. Driving tacks with sledge hammers. What is interesting here is that although many people know of the 30 Btu per sq. ft. limitation, few people know why floors are limited to that special number. It isn’t a physical limitation; it’s a human physiology limitation. If your skin is in contact with a surface greater than 85° F (the temperature of a floor at a room temperature of 70°) your body will assume it is going to overheat, and it goes into cooling mode, which means the people will be sweating. Not in my definition of comfort. Now you know …
“I can solder and am a licensed plumber, therefore I can do hydronics.” Plumbing and hydronics do have some very close relationships in that they both utilize pipes to transport water, but the similarities stop right there. Knowing how to solder does not automatically give you the proper knowledge needed to properly design, install, maintain and troubleshoot a hydronic system.
In the plumbing trade, you typically have 70 psi of driving force to move water through the piping system, whereas with hydronics, you have in some cases 1/10th that pressure to move fluid through a given circuit. In plumbing, although code requires the pipes to be “reamed to full bore with all shavings removed,” it is a rare day when the plumber will take the time to ream the pipes prior to assembly.
The art of radiant
“So what’s the big deal? None of our plumbing customers complain about pressure drops or fluctuations in their plumbing systems.” It is a very delicate balancing act. If attention is not paid to critical details, such as full reamed pipes and the location of the circulator or pump in relationship to the expansion tank connection, the system will not work as designed. Will it put out heat? Sure, but heat is just one component of comfort. My longtime associate John Siegenthaler provided me with a very interesting quote recently. We were talking about how our industry has lost sight of true “hydronics.” No one seems to take the time necessary to read and follow the instructions most manufacturers of critical system components provide with their equipment.
Siegenthaler said an old professor of his used to say, “You can’t do calculus without knowing algebra.” Ouch. He speaks the truth and as a former expert witness, I can attest to this statement. Some extremely important things must be taken into consideration in order for the high-efficiency comfort machines to be able to do their best. If just one link in that critical chain is out of place or improperly applied, the whole chain will suffer from poor efficiency.
One thing I have learned in my life as a hydronics technician is that even on systems where it appears nothing was done properly, the systems still put out heat. The end users will rally around the warmth. Remember, heat is but one component of comfort. If you are going to go to the time and trouble to call yourself a hydronics technician performing the art of radiant, it would probably be a good idea to get up to par on the science of hydronics that drives it.
“We only do staple up. It’s the cheapest way to go.” I think every contractor in America who has done radiant floors has had this feeling early in their career. I know I did. Then I realized I was dealing with one of the most efficient methods of delivering overall comfort, and decided “cheap” wasn’t a word commonly associated with this industry. I began looking at ways to make these systems more efficient, while maintaining the excellent level of comfort commonly associated with the installation.
I listened to Siegenthaler about “future proofing” my methodology of installation to make certain the water temperatures I had to use were as low as possible. Low water temperatures are a good thing when properly applied. I discovered extruded aluminum heat transmission plates allowed me to perform the jobs with significantly less energy consumption, and that is a good thing right? Comfort and efficiency trump cheap and easy any day of the week. I never wanted to be the cheapest bidder. I always strove to be the most comprehensive, all-inclusive bidder that provided the end user with significantly more value than my competitors.
If you’d like to learn more about the science behind hydronics, please consider joining the RPA at www.radiantpros.org/join. You will not regret it and you will be much better off in your efforts to become recognized as a true expert in the field of hydronics and radiant heating and cooling.