steam vs. hydronic

Jeff_67

Quick question for heatpros
Could you help me in explaining which system is more energy efficient (Steam or Hydronic) Any info., links, or facts would be appreciated. I'm a new tech and I've heard arguments for both sides. Also If you can give me any tips for making each system more efficient. I do work with customers with both systems that for the most part should be switched out, but the customers don't want to make an investment in a new high efficient system. Thanks for any info.

Al Letellier_9

most efficient

Here comes an often repeated answer....it depends.
Typically, FHW heat is more efficient in that you can zone easier, you can use reset, the heat is more evenly distributed and can be sized to the building. Most steam systems were built years ago, oversized and with boilers way too big. You can't reset steam, 'cause it still takes 212* to make it, and the radiators are stuck in a corner or under one window, it can be difficult to balance and is more finicky. Properly installed and controlled, a steam system with a modern boiler and a cycling control, can be extremely efficient and comfortable, but it takes a lot more effort and expense to make it so. So,......form your own opinion about it.

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Joe Brix

Taking water to steam

takes a given amount of energy that you can't get around. At least with non-oil systems, condensing and modulating equipment can be used to lower the water temps to the exact temp needed to match the heat loss.

Steamhead (in transit)

The other side of the coin

is that in a steam system there is less water to begin with. So you're boiling less water, which involves less energy input.

When you say "systems that for the most part should be switched out" are you talking about just replacing old, inefficient boilers- or tearing out entire systems? If the latter I can't see where that would be cost-effective. Same for trying to convert steam systems to hot-water- too many things can go wrong. Just install a good efficient boiler in either system, make sure the heat gets to the rooms efficiently once the boiler has done its work, and you're in.

I've also heard people say "it takes a lot more effort and expense" to make a steam system run efficiently, but have found the exact opposite to be true in practice. In almost all cases, steam systems that are not running efficiently can be fixed easily- all you have to do is get the basics right. I've personally saved a bunch from the scrapper by doing exactly that.

Steam has one big advantage over hot-water. When the system shuts down, the radiators and most of the pipes drain completely dry. The only pipes that will still hold water are the wet returns in the basement, and the boiler itself. So if the electricity goes out or Keyspan shuts down the gas supply, there's much less danger of freezing pipes and damage to the building. Sure, you could put antifreeze in a hot-water system but that's one more thing to maintain, and may run afoul of environmental or waste-disposal regulations in some areas.

When properly set up and maintained, a steam system will give the same comfort and approach the efficiency of hot-water.


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Tony Conner_2

You...

... do realize that the latent heat that the boiler must add to turn water into steam is what's given back in the radiators in the rooms when the steam condenses back into water, right? It's not a one-way trip.

Constantin

Some Additional random thoughts...

Steam systems benefit greatly from being vented properly, having their mains and other piping insulated, and having a proper header to ensure dry steam. For example, some luminaries here like to install drop-headers to ensure that only very dry steam goes into the distribution system.

Two-pipe and one-pipe steam systems are very different animals. They both use steam, but two-pipe systems apparently allow the retrofitting of orifice plates, for example, which would allow you to adjust the output from a radiator in ways that only a TRV can surpass. Many thanks to CTKay and Noel for pointing that out to me.

Plus, steam systems usually operate on very little electrical power and are allegedly freeze-proof. Riding out a storm with a steam system on a UPS should be easier than trying to do the same on any non-gravity hydronic system. There are some Darwinistic dangers associated with steam systems, such as the possibility of burning yourself or a little 'un but that usually only happens once.

Hydronic systems can operate at lower temperatures and thus may even offer the possibility of recovering latent energy in the flue gases. NG, Propane, and oil systems have 14%,13%, and 9% latent energy in their flue gases, respectively. Thus, you get your biggest potential return for a condensing appliance on the gas side. Plus, until the allowable sulfur contaminants in fuel oil are reduced significantly, most manufacturers will shy away from offering a condensing oil appliance in the US due to the experiences gathered 20 years ago.

The best bang for your buck long-term is weatherization and insulation. Get the building tight, then worry about how to heat it. Chances are, dramatic reductions in input ratings are possible. Only a heat loss will tell you how much a house will need, particularly after extensive renovations. Our calculated BTU/ft² needs dropped 4x, for example. Another benefit of the heat loss calculation is the ability to determine the required emitter sizes to keep the spaces comfortable. The larger the emitter area, the lower the required supply temperature, all things being equal.