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Gas heated steam radiator system

Hi,
I have a small dilemma regarding heating systems in our retrofit. We are renovating our brownstone row house in NYC such that it will have a tight air barrier envelope and moderate insulation (R30 in cellar ceiling, R 13.5 exterior walls, R6 windows and doors and R 45 roof. The house came with a cheap gas boiler and steam radiators. It didn't look in great shape and we were hoping to switch to mini-splits. But now we are running out of money and we are considering just getting the old gas boiler tuned up. Does anyone have any opinions on this? What are the implications of having a fairly blunt un-zoned heating solution for this medium performance house? Thanks, Daniel

Asked by Daniel Herskowitz
Posted Thu, 12/05/2013 - 13:48

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4 Answers

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Daniel,
A gas boiler and steam radiators, if the system is well designed, can certainly provide a comfortable interior environment. The sizes of the radiators are probably proportional to each room's heat loss. It's also possible to install non-electric zone valves to regulate the heat output of your radiators.

Answered by Martin Holladay, GBA Advisor
Posted Thu, 12/05/2013 - 16:12

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It kind of depends on just what shape the steam system is in: If this is a 100+ year old system with seriously rusted piping, or the pipes are running outside of your new insulation, you may want to consider other options.

But there are worse roads to travel than re-commissioning a functional steam heating system, and the higher efficiency the building envelope, the less the efficiency of the heating plant matters.

But there are several ways to boost system efficiency and comfort with old steam systems. To get reasonable temperature balance & flexibility you can effectively micro-zone 1-pipe steam with thermostatic radiator vents for well under $100/room, eg:

http://www.pexsupply.com/Danfoss-013G0140-Thermostatic-Rad-Valve-w-Vac-B...

http://www.pexsupply.com/Honeywell-V2043HSL10-1-8-One-Pipe-Steam-Thermos...

For more money you can even get them with wall-thermostats:

http://controlscentral.com/eCatalog/tabid/63/ProductID/327452/Default.as...

You can gain quite a bit of system efficiency by going that route, since you don't end up overheating some spaces in order to be comfortable in others, and you can set them back as-desired for sleeping, etc.

Tuning a non-modulating gas boiler is typically a once every 3-5 years kind of deal, but you should be able to get at least 75% raw combustion efficiency out of any steam boiler built in the past 20 years.

Tuning up the steam SYSTEM is also an important part of the re-commissioning- verifying that the system vents are working properly not stuck open or closed, etc. making sure the pressuretrol hasn't been over-cranked in response to gunked up vents, etc.

There is little rocket science involved, but since much of the world has moved on many HVAC pros are pretty clueless about steam (though in NYC you probably can find plenty of pros who aren't.) If you want to understand and maintain the system yourself (recommended), you can do worse than reading the annotated Torah chapters on it:

http://www.amazon.com/The-Lost-Art-Steam-Heating/dp/0974396095

The main system vents are usually out of sight, out of mind for the typical homeowner (who may not even be aware of their existence), and it's common to see systems with all new radiator vents and the system pressure cranked to 5 lbs or something ridiculous to make it all work, when the problem was a corroded up main vent. Normally you would only need to run it with the pressuretrol running between 0.5-1.5lbs (unless your Brownstone is 5 stories tall or something? :-) ), and if it's set higher, it's time back it off and to check all your system vents (it's typically just one), not just the radiator vents.

It's also pretty common to find the Hartford loop nearly rusted through (or actually seeping), since corrosion will be most-active at the boiler's water level in the plumbing. (The Hartford loop is the U-pipe on the return line prior to the boiler- explained here: http://www.massengineers.com/Documents/Hartford%20Loop.htm ) That's the most susceptible system piping, and it's common to see it all shiny and new, hooked up to the miserable old stuff, but if it isn't, that's where you should look for trouble first, and head it off before it becomes a problem if there is any serious question.

Answered by Dana Dorsett
Posted Thu, 12/05/2013 - 17:20

3.
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Heatinghelp.com. some serious steamheads there, including the author of the linked book

Answered by Keith Gustafson
Posted Fri, 12/06/2013 - 08:56

4.
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Thanks Martin, Keith, Dana,
These are exactly the resources I was looking for. I am not sure if the pipes are a hundred years old but there are pretty corroded especially in the cellar. I think the boiler itself is only about 7 years old. We will have to make a decision on it pretty soon. One negative is that if keeping steam is only a short term solution, then removing the pipes at a later date after the renovation, is a messy job. Thanks again for your help. Daniel

Answered by Daniel Herskowitz
Posted Tue, 12/10/2013 - 23:17

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