What Should We Be Saying About Open-loop Hot Water Heating Systems?

Do you ever get those anxiety dreams at night? The ones where the train is coming for you and the lights are bearing down, but you can’t get off the tracks because your muscles respond like molasses? That is how I feel every time I look at an open-loop hot water heating system.
As a refresher, an open-loop heating system is a water-based heating system in which the same hot water that heats the building can also be run for domestic supply—for showers and sinks. Before we wade into the murky gray area of what we should be saying about these systems and why, let’s go over how to identify an open-loop system and then look into some history of how we got to where we are today.
Tricks for Identification
Distinguishing open-loop systems from closed-loop systems can be complicated. One of the most basic characteristics of hot water heating systems is whether there are two water heaters or one. A building with two water heaters likely has one dedicated solely to heating, and thus it is a closed-loop boiler heating system. If the building has only one hot water heater for both heating and domestic supply, you need to look more closely.
If you see a mixing valve, you are probably looking at an open-loop system. The mixing valve is where the hot water for heating is mixed with cold water to set the temperature of the domestic hot water supply. In this configuration, the water heater can be set to heat to 140 degrees Fahrenheit or more for radiators and then tamped down with the mixing valve to 120 degrees Fahrenheit for domestic use.
Other distinguishing characteristics to look for are these flat, pan-shaped heat exchangers. If you see one of these, you are likely looking at a closed-loop system. This is because this heat exchanger separates the domestic water from the heating water. You could see both a mixing valve and a heat exchanger—in this case, you would likely be looking at a closed-loop system.
Finally, look at the water heater itself. Some water heaters separate the two types of water inside the heater. These types of water heaters typically have a “heating inlet” and a “heating outlet,” as well as inlets and outlets for domestic supply—so you will see at least four pipes connected to the water heater. These types of systems are generally closed-loop.
Armed with a few basic techniques for identifying an open-loop heating system, let’s look at some history to understand why these systems are being installed now and how they differ from traditional closed-loop boilers.
A Little History
I grew up in a house in New England that had a traditional closed-loop boiler system with galvanized steel pipes and cast iron radiators. The system was state-of-the-art when it was designed and installed at the turn of the century and, somewhat amazingly, it was still working well more than 80 years later when I was living in the house. In theory, with this old closed-loop boiler, if it had never leaked over the years, I would have been able to open up the distribution piping system and watch water come
out of the pipes that was put in when President Theodore Roosevelt was in office…antique water.
The noteworthy attribute of this antique water is how much less corrosive it is than the same system in which new water is constantly being introduced. The fresh water of an open-loop system delivers a constant supply of new, oxygen-rich water and is therefore more corrosive than its closed-loop cousin. Where I live and work now, in the Seattle area, I sometimes see 100-year-old galvanized steel boiler piping systems that are still in service in a closed-loop heating system, and yet the same steel pipe that was used for the domestic water supply has long ago failed and been replaced. That is the difference in the corrosive power between closed-loop and open-loop systems.
So if closed-loop systems work so well, why did we go away from closed-loop systems?
I don’t know what types of heating systems are used in your part of the country, but out here in the Pacific Northwest, these hydronic hot water heating systems with the Turbonic-type radiators just exploded into our houses starting in the 1990s (http:// www.turbonicsinc.com/). The flood of these heating systems rode in on the tide of new townhome construction that swept into many of our neighborhoods during this era, and the reason these systems got installed is simple: They are cheap.
As these systems became more prevalent, I found myself increasingly alarmed and confused by the lack of standards for installation. Each of these systems seemed to present a new, confounding array of pipes, tubes, manifolds, heat exchangers, timers, relays, mixing valves, solenoids, thermostats and water heaters. Occasionally, I run into one of these systems that looks so chaotic that I am reminded of a rugby scrum of octopi. Even if an inspector lacked all technical knowledge about hydronic heating, some of these systems simply look unreliable.
Adding to the confusion about these hydronic heating systems is this matter of open-loop versus closed-loop and the potentially corrosive effects of configuring these as open-loop systems, not to mention the greater risk from Legionella forming in the pipes of open-loop systems.
The fallout seems to be happening slowly. Every few months, a new recall or class action lawsuit bubbles to my attention. This started with the now-infamous Kitec and the IPEX system (http://www.kitecsettlement.com/faq.cfm), and followed in no particular order by Zurn and Q-PEX fittings (https://topclassactions.com/ lawsuit-settlements/open-lawsuit-settlements/3643-zurn-pex-pipe-fittings-class-action-lawsuit-settlement/), UltraPEX (http://ultrapexclassaction.com/) and Uponor (http://www.classaction.org/uponor-pex-problems). You can go online and find posts and blogs where professionals and laymen alike lambast open-loop systems as disasters waiting to happen, and yet these systems are still so widely installed that they could accurately be described as “industry standard.”
So, in light of all this history and knowledge we carry around, what should we be saying to our clients about open-loop heating systems?
Obviously, if you are looking at a tubing system that has been involved in a class action lawsuit and you are aware of this, the reporting gets a little easier. But what if there are no recalls or lawsuits that you are aware of? This is when I feel the heat from that spotlight on that train burning the nape of my neck, and I start thinking about the home inspectors in the early 1990s who were inspecting new-construction homes with LP siding.
Although we are technically not bound by the ASHI Standard of Practice to report on recalled products, I do believe it is our job to
educate our clients about what systems are contained in the home they are considering buying. Explaining to clients the drawbacks of open-loop heating systems—namely, that they are newer, unproven systems that seem to be having reliability issues due to the corrosive effects of the water, as well as being associated with potential health issues related to having stagnant warm water in the pipes—would seem to be a professional duty.
I always recommend having these systems serviced by a professional hydronic heating contractor, and I recommend that my clients obtain opinions and estimates for converting their open-loop system to closed-loop for the reasons discussed in this article. I have seen estimates that range from $2,200 to $2,800—these prices may vary by region. A logical time to make this conversion is when the water heater reaches the end of its 10- to 12-year service life and replacement of the existing water heater should be on the table anyway. However, with so many variables in how these systems are installed, I find it difficult to say with any accuracy how urgent such work is and how reliable some of these systems will be even after being converted to a closed-loop system.
I have only glanced over some of the technical issues with these systems in an effort to have a manageable article that is provocative and at least moderately enjoyable to read. I hope that I haven’t oversimplified the issues and that I have provided a platform for discussion. I welcome any differing opinions on how other inspectors handle these systems. To get in on the discussion, see my blog (http://getscribeware.com/blog) and the ASHI discussion forum (https:// www.homeinspector.org/).
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