Red-hot Radiant Key for Blue Barn

By Bob "Hot Rod" Rohr

Radiant expert

For the past six years the "blue barn" that my wife Helen and I remodeled into a home for her folks has been radiantly heated. It is by far the part of the project that my in-laws, Nic and Eleanor, have enjoyed most. They keep a scrapbook on the coffee table to show all takers. In it, photos of the remodel project show tubing installations and some of our horsing around as the job neared completion - the perfect conversation starter on a cold fall evening.

The blue barn is just a hundred yards from our place, perched on a small rise above our golden pond. Their home had a conventional cast iron boiler with a 40-gallon indirect tank as the DHW source. It's served them well since they've lived here. It was a fun project and a very common hydronic approach back in the 1990s.

But I do notice the propane delivery truck "hosing up" each and every month. I replaced my own cast iron boiler with a mod con last fall and have seen my propane delivery buddy but once this winter. And so I've wished for the heating system at the Blue Barn to enjoy the same loss of appetite for fuel that we've experienced this past heating season.

At last I had the opportunity this spring to do some upgrades to their hydronic system. Central to the project was a shiny new wall-hung modulating condensing boiler, the perfect companion for the Blue Barn's slab-on-grade radiant system.

Better yet, it had built-in DHW capability. I was a bit reluctant to trust this smallish looking DHW module. True, it's only Nic and Eleanor that live in the home and their DHW use is very small. In fact, the boiler was so small and compact that I was able to wall mount it right next to the old system and allow that one to operate right up to the point where I had the mod con boiler
all piped, vented, wired and fired up.

This particular low NOx, sealed-combustion, fully-modulating mod con boiler is available in three sizes: 126, 167 and 242 MBH input. It provides 96% system efficiency at high-fire. The 126 MBH unit (at just over 100 hanging pounds) has optional DHW heating, so it was the perfect size for the Blue Barn. The unit also comes with standard, built-in bladder-type expansion tank, two air elimination vents, backflow preventer, ISO valves and unions, and a three-speed circulator. The water manifold has built-in reverse pressure bypass to prevent short-cycling. The unit's control also provides pump and time delay, exercise and freeze protection.

Great stuff, but I still wanted to test the waters first. So I opened three faucets in the home and recorded the hot water temperature as they flowed for a good 20 minutes. Sure enough, the unit put out an honest 3.5 GPM from the 55 F well water to the 104 F preset. Now I'm a believer. Fortunately, there's an upstream water softener, so I'm comfortable the mod con boiler will keep producing plenty of DHW without risk of fouling the heat exchanger.

The boiler install was a breeze. A paper template included with the boiler located all the mounting holes. The bracket was lag bolted to the wall; the boiler slipped over the bracket, and piping connected. A nicely powder coated concentric vent assembly looks clean and unobtrusive on the sidewall of the mechanical room. The mod con boiler was whisper quiet. It fired on the very first try.

Hot Rod puts the finishing touches on the blue barn's radiant system, making a minor adjustment to the boiler.

I included my typical "mod con" package on the install. I used a small HydroLink to assure flow through the boiler as the two radiant zones cycled on and off. Properly installed, the HydroLink has worked very well for me as the system's only air removal point. I install quality purge valves will full port openings to flush and purge the system.

The combination of the high-mass on-grade slab and some higher-temp suspended tubing for the second floor meant that the hydronic system needed to provide both high and low temperate mixes. This was accomplished by using a three-way thermostatic mixing valve.

The Hydrolink low-loss header performs the function of a parallel primary loop. The key detail is the unit's performance as a hydraulic separator between the boiler and the load circuits. Its purpose is to connect the secondary circuit to the primary loop while eliminating any tendency to influence flow in the secondary circuit. This permits several circulators to co-exist within the same system without getting into a tug-of-war, competing for water pressure.

The unit provides a low-pressure loss zone, allowing both primary and secondary circuits to be hydraulically independent of one another. The low loss header is especially important for use with the new generation of high flow-resistant, low-mass condensing boiler installations because it moves the point of lowest pressure drop from the boiler to the unit's low pressure chamber. The distribution manifold has closely spaced tees, which connect the secondary circuit to the primary loop internally so that flow in the primary loop has little or no tendency to influence flow in the secondary circuit.

And, Grundfos SuperBrute pumps are also a big advantage on many of my jobs. The wet rotor circulators, now in three sizes, have three speeds to choose from and come with an internal flow check to eliminate "ghost flow." With the flick of a switch, various speeds can be chosen, easily changing head and flow to meet the specific needs of the system.

By checking the delta-T for either of the zones, I can adjust a multi-speed pump to operate within the most desirable pump curve. That saves energy and promotes longer pump life.

Grundfos engineered in two other advantages. The multi-speed pumps have super-high starting torque, made possible by a starting torque booster that pulsates DC current into the winding, making the pump act like an impact driver, virtually eliminating no-start situation. It also has an integrated, removable check valve that doesn't reduce pump performance and eliminates the expense of an inline check valve.

An autofill valve also allows me to "up" the pressure easily to power purge. Merely turn the dial back to the 12 psi position when the purge is complete.

Grundfos SuperBrutes mate to the HydroLink with the new Grundfos ISO flanges. These cleverly-designed components provide dielectric isolation using a large port ball valve with unobstructed flow to the circs.

The win for Nic and Eleanor is a sleek, ultra-efficient boiler with state- of-the-art hydronic management provided by Caleffi and Grundfos components. The next step is to update the coffee table scrapbook with all the mechanical room upgrades. Shouldn't be a problem: we've been brushing-up our photography skills, too.

 

Bob “Hot Rod” Rohr is particularly interested in “hybrid” radiant systems – systems that utilize solar and wood energy in addition to, or in place of, fossil fuel. Also, systems that incorporate different methods of heat delivery. He owns and operates Show Me Radiant Heat and Solar, Inc. in southwest Missouri. Reach hot rod at hotrodradiant@aol.com or by phone at (417) 753-3998.