When housing starts are down, offer hydronic retrofit solutions.

Figure 1. Drawing by John Siegenthaler.


If you follow news reports, magazines and Internet posts about home building, you’re accustomed to the fact that new home construction is sluggish at best, and it’s almost nonexistent in some overbuilt markets.

As new home construction goes, so go sales of hardware for radiant panel heating. This trend surfaced rather abruptly in 2009 in sales tracking data supplied by the Radiant Professionals Alliance, formerly the Radiant Panel Association. The good news was that the decline in sales of radiant heating hardware wasn’t dropping as fast as new housing starts. The bad news: The “glory days” of the 1990s and first part of the new century - times when annual increases in sales of radiant hardware sometimes topped 25% - were over.

Based on information in the building trade media, it doesn’t look like the housing booms of the past will be returning anytime soon. However, many of these information sources also point out there has been a significant uptick in residential remodeling. The National Association of Home Builders forecasts 5% growth in remodeling in 2011, followed by 10% growth in 2012.

Owners of existing homes haven’t just drawn their curtains waiting for the economy to recover to its pre-recession days. Many are moving ahead with modest remodeling efforts to improve their existing homes. So, as Dale Carnegie once suggested, “When life gives you lemons, make lemonade.”

Purveyors of hydronic heating systems are well positioned to take advantage of this growth trend in remodeling. Although any type of heating system could potentially be included in a remodeling project, certain hydronic options offer attractive and often unmatched benefits.

Figure 2. Photo by John Siegenthaler.

The Ingredients

You can’t make lemonade without water. A given volume of water can store almost 3,500 times more heat than the same volume of air. This is what allows hydronic systems to operate with small “conduits” (tubes) compared to those required in forced-air systems (ducts). 

Given standard design criteria, a 1/2-inch size PEX tube carrying heated water can transport heat at the same rate as an 8-inch square duct or a 9-inch diameter round duct. The 1/2-inch PEX tube is easily routed through or along framing cavities as seen in Figure 1.

Either of these ducts could be accommodated only in the space between parallel floor joists - assuming no structural bridging, wiring or plumbing is in the way. Routing such ducts perpendicular to the joists usually requires building exposed soffits or shoving the ducts up into unheated attic space. The ability to install hydronic heating using minimally invasive procedures is a huge advantage in retrofit and remodeling situations.

I like to tell people that if you can pull an electrical cable from point A to point B within a building, you can just as easily pull through some small diameter flexible PEX or PEX-AL-PEX tubing for a home-run distribution system.

Add Some Zest

The heat emitters chosen for a hydronics retrofit strategy should be easy to install. In my opinion, panel radiators are by far the least invasive and easiest to install option for retrofit applications. They’re available in a wide variety of shapes and sizes to fit existing wall spaces and heating loads. They are relatively light and can usually be supported on existing studded walls without additional blocking. Piping is passed up through the two small holes in the floor as seen in Figure 2.

The panel radiator shown in Figure 2, as well as each of the other panels in the building, is equipped with a wireless thermostatic radiator valve. These valves allow room-by-room temperature control, something that few houses without hydronic heat enjoy. It’s all accomplished without wires, batteries or those annoying little black box transformers. Just set the knob on each radiator valve for the desired comfort level and let the valves continually adjust the flow as needed.

Figure 3. 

Stir In a Little Sugar

Another important ingredient in the mix is a pressure-regulated circulator. When set to provide constant differential pressure it’s an ideal match for a home-run distribution system and panel radiators. Given how pricing on these ECM-based circulators has dropped recently, you can buy one for less money than a standard circulator along with a differential pressure bypass valve. The latter is required whenever a standard circulator is used with valve-based zoning. The “sweet” thing here is that the pressure-regulated circulator does its job using only about 30% of the electrical energy of the standard circulator. Lower installation cost, substantially lower operating cost and the simplicity of a single circulator distribution system. What’s not to like?

Ready To Serve

Figure 3 shows a typical schematic for the retrofit strategy we’ve been discussing. 

This system uses a high-efficiency mod/con boiler with its own internal reset controller to provide “cruise control” of the supply water temperature to the home-run distribution system serving the panel radiators. Each panel has been sized to the design load of the room it serves, based on a supply temperature not to exceed 140º F and a temperature drop of at least 30º F. This ensures the boiler will operate in its condensing range at nearly all times.

A pressure-regulated circulator configured for constant differential pressure mode also provides cruise control for flow through the home-run distribution system. The circulator’s speed automatically adjusts as the wireless radiator valves open, close or modulate.

This schematic assumes that the boiler has a high head loss characteristic, and thus requires a separate boiler circulator to ensure adequate flow whenever it is firing. Although such a scenario is typical of today’s hardware, evidence is mounting that low head loss mod/con hydronic heat sources could soon set a new standard for both high thermal efficiency and high hydraulic efficiency. These new heat sources would be “flow through” designs that eliminate the need for a separate boiler circulator. This means one less circulator to install and feed with electrical energy over the life of the system.

An indirect water heater has been included in the system. When you sell a customer on a state-of-the-art space heating system, why not use the same boiler for providing DHW?

The hardware and system concept we’ve just discussed is ideal for retrofit opportunities.  It uses state-of-the-art hardware in a simple and elegant configuration. One that’s highly adaptable to different site conditions. Use it when life hands you some lemons.<

Links