None shall pass

By Bob "Hot Rod" Rohr,

Radiant expert

Air -- can’t live without it; can’t live with it churning up your hydronic systems.  

Air elimination in a hydronic system is an area which installers need to pay close attention to. It can be easily addressed with some prior planning and proper component selection. Lack of attention to this detail can punish you with noisy systems, air locked systems, “no heat” call backs, component failure and system corrosion, to name a few common consequences.

Luckily, there are a plethora of products available today to make your systems perform quietly and efficiently.

A properly placed ball valve with a boiler drain installed nearby is one of the simplest air removal devices. These components could be installed on every hydronic loop or zone. Some radiant manifolds offer purge cocks and even small auto vents mounted right on the manifold.

Properly placed, one ball valve at the return piping near the boiler and a single boiler drain could be adequate to purge the entire system.

Several valve manufacturers now offer a one-piece ball valve purge cock. I have used both the Webstone and Watts versions. These valves provide a clean, easy-to-use purge option with two solder or threaded connections.

Many boilers have air elimination features built-in, or onto, them. Cast iron boilers will often have an area designed to trap and remove air with a simple float-style air vent. I’ve noticed virtually all of the modern mod-con boilers have a small air vent, or valve, on the heat exchanger header. Some brands supply the necessary fittings, along with an air vent to be installed at the job  site.

In some cases a single air vent at the high point of the system, with proper purge cocks, may be all you need.

There is a lot more potential for air problems in large radiant systems with multiple zones of thousands of feet of tubing. In these situations, you may be better served with an auto vent air scoop or air scrubber. A properly located, inexpensive iron air scoop is an amazingly reliable and effective component. Many brands are available and they offer numerous tapings to install an air vent, expansion tank and fill valve. Cast iron air scoops have been used successfully for many, many years and they are still a good, economical and multi-purpose fitting.

Perhaps the most efficient removal device is the micro-bubble re-sorbers. Look for these from most of the hydronic component manufacturers. I have had excellent results with the Spirovent, Caleffi, B&G, Honeywell and Taco brands. Most are now available as a threaded or sweat version. Some are offered in configurations for vertical mounting.

This type of purger uses a screen or mesh inside to capture the smallest of air bubbles as the fluid flows through them. They seem to work faster than the scoop type mentioned earlier. The air-scoop purgers depend on a ramp inside to coax the air to the vent. I have found micro-bubble re-sorbers to be a little more forgiving in terms of their location in the piping, and they are excellent devices for systems with a lot of piping and places for air bubbles to hide.  

In some systems, several removal devices can work better than just one. A classic example would be an injection mixing system. It is a slow process to try and remove the air across those closely spaced, often small diameter injection bridges. I’ll use a micro bubbler on the radiant side, and an air scoop on the boiler piping. If the boiler or heat source has provision for an air removal device, by all means use it on the boiler side of the injection bridge.

Hydro separators are all the rage these days. They offer an excellent way to hydraulically disconnect the boiler from the system piping. And they also bring the added feature of air removal. The brands I have used all have a domed top with a provision for an air removal device.

Nothing beats a good power purge as the first step in air elimination. Use full port valves to allow for a good flow rate. You may be amazed how much crap, in addition to air, flushes out of a brand new installation. Copper shavings, solder balls, wood chips, small gravel or debris left behind from the manufacturing process may be lurking inside those systems.

Select an auto-fill valve that allows you to crank the pressure up to aid in the power purge. Keep the

pressure five psi or so below the boiler relief valve setting, of course. Or add some valves to isolate the boiler and expansion tank from the rest of the piping. Remember to check and adjust the air charge in the expansion tank when you install or bring them online.

On a recent mod-con installation I installed a full-sized Webstone purge ball valve right at the boiler connection. This allowed me to purge through the indirect coil, purge the air from the boiler heat exchanger and purge my radiant loops. All from one location. See the Hydronicad drawing on the previous page.

Clear vinyl hose works great for assuring a good clean purge. Purge until it is bubble-free, but also until the milky color disappears. That foggy color indicates air in the solution. You should be able to purge until you get a good clean, clear, quiet flow.

One last valve to keep in your bag of tricks is a combination ball valve with two purge cocks. You will often see this valve used in thermal solar piping. It allows you to flow into and through the loop at one location with the twist of a few handles.  

You may have noticed many of the European components arrive with purge cocks that don’t like our garden hose fittings. They use a hose fitting with an o-ring on the face to make the seal. You can get this fitting from most of the Euro fitting suppliers. Keep a few hoses on your truck with this fitting or solder up some “metric” hose adapters. 

May your lungs be filled with life-giving air...and may none pass through your hydronic piping.

Bob “Hot Rod” Rohr has been knee-deep in plumbing, heating and solar work since he was a kid. He has learned a lot of simple ways to install, repair and update hydronic systems. Check out his new, downloadable “Cool Tips from Hot Rod” at www.showmeradiant.com.