Proper Installations: It’s All About Beer


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Most jobs I am called to look at are due to a lack of understanding how to properly install a new low mass modulating condensing boiler. I’m not alone in this finding. Every boiler sales manager and tech service person I talk to says the same thing.

If you stopped and thought about it for just a minute, you would realize it’s really all about beer! Take a moment and imagine an empty pint glass. Not a frozen pint glass mind you, that would be improper, but a room temperature pint glass. Now fill that glass with your favorite beer. In your mind I want you to imagine reaching out and picking up that beer. What do you sense? The anticipation of malted barley? Th e smell of hops? The crispness of the yeast? You reach out, you touch the glass. What does your hand feel? Condensation!

The outside of the glass is condensing! This is caused by the difference in temperature between the cold beer and the warm room. This is similar to what happens when we return cold system water to a hot boiler. This is exactly how we DO NOT want a cast iron or steel boiler to work, but EXACTLY how we want a modulating-condensing boiler to work! By getting the products of combustion to condense in a modern modulating condensing boiler we extract not only the sensible heat, but the latent heat, too. This will take our boiler efficiencies from 84% to 91% and higher!

In the old days, our great grandfathers installed huge cast iron boilers on systems with three inch mains. These systems, called gravity systems, worked by the boiler heating the water, the hot water rising up the large main piping, then up the smaller pipes to the radiators all the while the cold water is falling back to the boiler. The cast iron and steel boilers did not condense, because the flow was dictated by the rate of the water being heated, which allowed the boiler to reach and work at temperatures above 140°F.

Then along came smaller cast iron boilers with forced circulation. All of a sudden we have changed the system to boiler water content ratio dramatically. Installing one of these “lower then original mass boilers” on a gravity system requires some special rules. One of the special rules is to install a bypass loop to keep the boiler from condensing as shown as a dotted blue line in Figure 1. This allows the system to have one flow rate and the boiler to have another flow rate. In this case SLOWING the water flow through the boiler to allow the boiler to come up to operating temperature faster, so as to keep the products of combustion from condensing in the boiler. A gas fi red boiler will condensate when the return temperature is below 140°F. Flue gas condensate, which is very corrosive, will destroy a steel or cast iron boiler.

Figure 1
Figure 1

Now bring on today’s modulating condensing boilers, which are even lower mass. Instead of being the 800lbs. gorilla in the room, they are now the 100lbs. monkey in the corner. The number one installation error is not understanding how to correctly install these low mass boilers using primary/secondary piping. In reality we are basically going to do the same thing we did when we changed from a huge boiler on a gravity system to a smaller cast iron boiler with forced circulation, we’re going to install a bypass.

Installing the bypass will differ in the respect that now we are going to install the bypass using forced circulation by installing multiple circulators and a Low Loss Header (LLH). Don’t let the LLH intimidate you. You can spend hundreds of dollars on one from multiple manufactures or you can simply use two closely spaced properly sized tees, see Figure 2. The important factors are properly sized tees and properly sized boiler circulators. Break out the knee pads…I mean the Installation and Operation Manual!

Figure 2
Figure 2

By installing the bypass with the proper circulators we can assure proper flow through the heat exchanger assuring that; (a) the boiler will stay in condensing mode longer, (b) have proper flow to keep the boiler water passageways clean, and (c) the boiler will not shut off on high water temperature limit.

All modulating condensing boiler manufactures will tell you that the BEST PRATICE is to install their boilers using primary/secondary circulation. Take it from the pro’s, avoid problems, and do it right the first time. When you’re all done you can sit back and admire your craftsmanship while enjoying a nice cold beer, because after all, it’s all about beer.

Steve Wieland
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Posted In: ACCA Now, Hydronics

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