Hot water boilers and systems

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Often, the best way to heat a building is by warming water and moving it gently through pipes and radiators to portioned areas of a given space. We call those spaces “zones” and we call that type of system “hydronic” heating. Of the 15% of U.S. homes heated with circulating hot water systems or steam, the northeastern United States has the highest concentration. That’s right, 85% of our country is heated with forced air/electric/heat pumps, etc. Only the residents of our coldest climates tend to invest in hydronic heating systems while most of Europe uses hydronics because the efficiency and adaptability to changing conditions is much higher than with most other options.   Hydronic systems often perform better than steam systems because they have greater flexibility by giving us the ability to use varying water temperatures, smaller pipes, don’t rely on things like critical pipe angles, use smaller boilers with much higher efficiency ratings, and have far more options for control and exhaust venting. While all steam boilers offer a maximum efficiency of about 80%, hydronic heating boilers are reaching ranges from 82% (standard efficiency) and 85% (mid-efficiency) to 96% (high efficiency). The goal of high-efficiency boilers is to heat with much lower water temperatures than other boilers, but that produces some effects that have to be dealt with. Because they extract so much heat from their gas-burning flame, their flue, or exhaust, gases are much cooler than that of standard-efficiency boilers and by-products of combustion take on different characteristics. When carbon-based fuels go through the combustion process, they produce carbonic acid that gets trapped in water vapor which is most often carried out in an unharmful form with the hot exhaust as it rises through a vertical chimney. In a high-efficiency boiler, much more of the heat energy contained in that hot exhaust is extracted and put back into the system’s heating water and sent to the radiators. The carbonic acid that is formed in all boiler exhausts is then not hot enough to remain a vapor and it instead becomes water. That water will eat through your masonry chimney in no time and the presence of carbon monoxide in the living space becomes a very real concern, in fact, it’s practically inevitable. So, the way we vent mid-to-high-efficiency boilers has to be different than conventional methods to properly handle that acidic flue condensation. Your brick chimney alone is not a viable option to convey this destructive gas to the outdoors, but stainless steel vent piping and some plastics are safe materials for exhausting these boilers and the preferred method for routing these is out a side wall of the building to a safe area that is 4 feet away from any building openings such as doors and windows. That means 4 feet in all directions from the center of the pipe which penetrates the side wall. Try finding an 8-foot circle clear of a door or window in your attached NYC building and you’ll face a real challenge. I’ll bet you can’t. So there is another approved option: use the building’s brick chimney as a chase to either line with an appropriate lining material (which should be done regardless of what type of boiler at whichever efficiency you’ve got as brick and mortar are not good materials for venting any flue gases at all) or lower a plastic or stainless steel pipe of much smaller diameter down from the roof and attach it to the boiler in the cellar. Most HE boilers only require a 3” or 4” flue pipe compared to the 6”-10” flues of standard-efficiency boilers. This is not always a simple process, but is the best way if not the only way to use high-efficiency equipment in many cases of an attached townhouse or multi-family building.  In easier worlds, or the suburbs and rural areas outside of any major city, detached homes give us 4 walls to select a venting method but we’re often limited to two in our area, or even one if you’ve got a Landmarks issue. It’s important to know that the condensate that collects in the high-efficiency vent piping has to be collected and neutralized once it is automatically drained from the boiler and put into our plumbing drainage systems. That’s a simple process that boiler manufacturers provide for initially and is easily dealt with in the field by professional installers, but again, it is something that needs to be dealt with in a smart, planned way.   Also, high-efficiency boilers have a much higher off-the-shelf cost than traditional boilers and venting can be costly in some cases. When the combined costs are prohibitive, standard-efficiency boilers, when sized properly, are still a legitimate efficiency-upgrade option and when installed smartly with some additional piping and electronics, can reach seasonal efficiencies, or AFUE ratings, close to their much more expensive counterparts even though technically their *combustion efficiencies* are significantly lower. Combustion and seasonal efficiency ratings can be confusing, can sometimes be misleading, and are often misunderstood, but they both directly relate to economy of fuel usage and money savings. A plumbing company that keeps up on the newest technology and installation methods and codes is best suited to give you your most viable options.   An installer has a lot to think about when selling a new hydronic boiler and other heating components. There are many types of boilers on the market and the tens of manufacturers in the U.S. alone each make 5 to 10 models, each of them at different outputs, available to the consumer and because field conditions vary so greatly there may only be two or three that can possibly work in your building. Once a boiler is selected, there are options to consider, like how to make your number of zones work together and separately, how to pump the water through the system (too slow and the efficiency and boiler both suffer, too fast and the pipes erode while making odd noises), what is a good water temperature to maintain in the system (too cool and the home won’t heat well, too hot and you’ll lose money burning fuel unnecessarily), how much control should be made available to the owner/tenants, etc. Would I give a crazy tenant access to the thermostat settings? No way. Would I let a willing and capable client, after reading the Operation Manual or having been given some basic and targeted instruction, adjust the boiler’s water temperature at will? Sure I would.   All in all, hydronic systems have many benefits over steam heat especially considering how well they make domestic hot water for our sinks, showers, etc, using indirect water heaters, but getting them to perform to their highest practical potential takes planning, best product selection, monitoring, and maintenance.   Steam systems just take a good initial installation and then an annual service in most cases because of their inflexibility and lack of moving parts.   Take a look at your hydronic boiler this autumn and see if anything looks like it needs attention: do you see any rust or evidence of leaking? Does the pressure gauge show a reading? The pressure in your system should be the measurement of the height from the base of the boiler to the top of the highest radiator multiplied by .431 plus 4psi. So let’s say there are 35 feet from the boiler to the top radiator: 35 x 0.431 = 15.08 + 4 = 19psi. Your boiler’s gauge should read a minimum of 19psi. Your boiler may only be able to handle 30psi, so you don’t want it significantly higher than 19 or 20 psi. Here is one of those cases where more is not better.   Cool weather is right around the corner and while there is far too much to cover in a conversation about hydronic heating systems for a Brownstoner post, I hope this text answers some questions you may have about your system or a system you are considering converting to in the future.   Thanks, Master Plvmber www.GatewayPlumbing.com