Is 1 pipe steam more efficient than 2 pipe?

tkos115

So today the thought crossed my mind whats more efficient, a 1 or 2 pipe steam system? Or perhaps they are equally the same if they are both set and piped correctly. I just have a 1 pipe system which seems to work pretty efficiently, however I've never had a 2 pipe system or talked to someone that has had one to compare it to.

Jamie Hall

I'd have to say that so far as the radiation and mains and return piping, just about the same. Vapour two pipe may have a slight edge since it runs at a lower pressure, but normal two pipe vs. single? Not much in it, all else being equal.

ChrisJ

Jamie Hall said:

I'd have to say that so far as the radiation and mains and return piping, just about the same. Vapour two pipe may have a slight edge since it runs at a lower pressure, but normal two pipe vs. single? Not much in it, all else being equal.

What about a system like mine running a fraction of an ounce?
I have less piping than a two pipe system and many of my radiators are held back, often completely off.

SuperJ

Good point, less pipes in cold basements and cold wall cavities should equal a bit of a efficiency boost everything else being equal. (house should heat to the same temp with a bit less gas).

Jamie Hall

I wonder just what the heat loss from the returns really is. Considering the huge difference between the amount of latent heat in the steam and the sensible heat in the condensate... Even if the condensate gets cooled 100 degree F on its way back to the boiler, that's only a fraction of the heat in the system that's "lost".

Hmm... where's my sliderule?

ethicalpaul

If I can butt in with a quick question: Why was 2 pipe introduced? Was it to more easily allow the residents to modulate the heat by partially closing the supply valve?

In the building I work in, half of it was built first, then they expanded the footprint some years later by basically building another one just like it adjoined to fill the rest of the block (470 S. Park Ave NYC, "The Silk Building"). In the older half it's one-pipe and in my half, it's two-pipe so I guess we straddled right across that tech advance.

PS: so maybe that is a vote for 2-pipe's efficiency: you can send less steam to rooms that need less heat

ChrisJ

ethicalpaul said:

If I can butt in with a quick question: Why was 2 pipe introduced? Was it to more easily allow the residents to modulate the heat by partially closing the supply valve?

In the building I work in, half of it was built first, then they expanded the footprint some years later by basically building another one just like it adjoined to fill the rest of the block (470 S. Park Ave NYC, "The Silk Building"). In the older half it's one-pipe and in my half, it's two-pipe so I guess we straddled right across that tech advance.

PS: so maybe that is a vote for 2-pipe's efficiency: you can send less steam to rooms that need less heat

I honestly do not know the answer, but my guess is 2 pipe was first and 1 pipe was a cheap system introduced later.

2 pipe is definitely easier to control.

JUGHNE

From reading Dan's books, IIRC, 2 pipe came along once some form of radiator steam traps were available. One selling point was no air vents in the living space. Noises, smells and water spitting were in the basement where people thought they belonged.

I believe 2 pipe wins because:
Throttling steam by valves, TRV's or orifices.
Smaller piping.
No counter flow piping on run outs to radiators.
Heat loss from return lines is usually in the heated structure anyway.

KC_Jones

ChrisJ said:

2 pipe is definitely easier to control.

This is my vote.

Think about all the zoning, smart thermostats, WiFi that people want now, it's nothing new it's just in a different form.

ChrisJ

Single pipe steam should called "Steam heat Lite".

tkos115

It seems like 2 pipe is more "user friendly", in a sense because it can be controlled better and set more to someones preference. So my other thought would be, does a 2 pipe require more maintenance, or prone to more issues? My guess is it can't be much more work other than they use steam traps? But I guess that isn't much different than a 1 pipe uses vents.

PMJ

tkos115 said:

It seems like 2 pipe is more "user friendly", in a sense because it can be controlled better and set more to someones preference. So my other thought would be, does a 2 pipe require more maintenance, or prone to more issues? My guess is it can't be much more work other than they use steam traps? But I guess that isn't much different than a 1 pipe uses vents.

Around me it is the higher end homes that have 2 pipe. Better control, but higher cost to install. Seems like one-pipe was a way to get by with significantly lower installation cost.

2 pipe is easier for the average person to control and make changes room by room. Maintenance actually lower as some 2 pipe systems have way fewer moving parts than one pipe. Several systems had traps with no moving parts at all. One vent on the dry return and that's it for moving parts away from the boiler.

DanHolohan

One-pipe came first.

The Steam Whisperer

I suspect two pipe is more efficient. While there are more pipes to loose heat, they are much smaller for 2 pipe. I suspect it is the heat delivery to the room that would make 2 pipe more efficient. One pipe steam radiators heat section by section so the air is very hot as it exits the top of the radiator. For two pipe the steam spreads across the top of the radiator, so the air is heated to a lower temp, but more air is heated. During typical operation, both radiators are only partially heated, but the one pipe supplies much hotter air that would tend to race to the ceiling and stay there. 2 pipe is probably more gentle and the air temperature stratification less severe.

ChrisJ

> @The Steam Whisperer said:
> I suspect two pipe is more efficient. While there are more pipes to loose heat, they are much smaller for 2 pipe. I suspect it is the heat delivery to the room that would make 2 pipe more efficient. One pipe steam radiators heat section by section so the air is very hot as it exits the top of the radiator. For two pipe the steam spreads across the top of the radiator, so the air is heated to a lower temp, but more air is heated. During typical operation, both radiators are only partially heated, but the one pipe supplies much hotter air that would tend to race to the ceiling and stay there. 2 pipe is probably more gentle and the air temperature stratification less severe.

90% of the time my vents are literally cold to the touch. Rarely does steam get near them and I guess the air being pushed out is cooled by the cold cast iron.

On occasion a few vents will get hot but usually only during cold snaps.

mikeg2015

1 pipe can have TRV’s too, so that advantage is null. it can be balanced with adjustable vents... somewhat.

Less pick up from less piping still seems like a significant advantage.

I’m another with a fractions of an ounce system. I have a temp gauge for my indirect tank. Never goes over 212. But... is 3F really that much different in economy? For header losses or actual combustion efficiency. I’m not really convinced.

Would be nice to see a test so we can quantify it better.

ChrisJ

> @mikeg2015 said:
> 1 pipe can have TRV’s too, so that advantage is null. it can be balanced with adjustable vents... somewhat.
>
> Less pick up from less piping still seems like a significant advantage.
>
> I’m another with a fractions of an ounce system. I have a temp gauge for my indirect tank. Never goes over 212. But... is 3F really that much different in economy? For header losses or actual combustion efficiency. I’m not really convinced.
>
> Would be nice to see a test so we can quantify it better.

I have TRVs on 5 out of 10 radiators.
Yes they work but I'm sure not as good as a 2 pipe system.

For example you can stop a 2 pipe radiator from heating or reduce it's output during a cycle. You cannot do this with 1 pipe steam so TRVs rely on more cycles.

mikeg2015

My TRV will stop a radiator heating when it above setpoint. Can turn it off by turning it down to minimum. It will stop it during a cycle. However it cannot throttle the heating rate. I would need an adjustable vent for that.

You can also still close off a radiator completely using the valve. But better and easier to use the TRV.

WOuld be nice if ventrite made a vertical adjustable vent.

Overall 2 pipe is genrally superior, but I’m not sure it would nessesarily be more efficient.

PMJ

From a fuel efficiency only basis I'm guessing there isn't enough of a difference to talk about between 1 pipe or 2 if the systems are both well run ultra low pressure.

All in cost overall efficiency I bet 2 pipe better due to fewer moving parts to fail and less/simpler troubleshooting so fewer service calls. Regular folks can figure out whether the inlet valve is open or closed.

ChrisJ

> @mikeg2015 said:
> My TRV will stop a radiator heating when it above setpoint. Can turn it off by turning it down to minimum. It will stop it during a cycle. However it cannot throttle the heating rate. I would need an adjustable vent for that.
>
> You can also still close off a radiator completely using the valve. But better and easier to use the TRV.
>
> WOuld be nice if ventrite made a vertical adjustable vent.
>
> Overall 2 pipe is genrally superior, but I’m not sure it would nessesarily be more efficient.

This is strange because none of my TRVs can stop or reduce a radiators output once the air is out. Once it's got to a point, that's it, it will continue that amount untill boiler shuts off regardless if what the trv does.

Also, all of mine can throttle the venting.
If it's close to the set temp it will vent very slowly. If it's much cooler it will vent faster.

As far as I know, all of them behave this way.

I have two Danfoss and three Macon. All 5 have vacuum breakers.

I don't see how the TRV could possibly push the air back into the radiator and the steam out to stop it from heating?

ChrisJ

> @PMJ said:
> . Regular folks can figure out whether the inlet valve is open or closed.


You sure about that?

PMJ

ChrisJ said:

> @PMJ said:

> . Regular folks can figure out whether the inlet valve is open or closed.





You sure about that?

Just optimistic I suppose!

mikeg2015

> @ChrisJ said:.
>
> I don't see how the TRV could possibly push the air back into the radiator and the steam out to stop it from heating?

Once air vent closes steam condenses and leaves as condensate. But it would have to wait until the next cycle to refill with air.

I don’t have vacuum breaks on mine, but they seem to work fine. Maybe the Honeywell trvs lift under vacuum in one direction.

I have to watch mine. I have a small radiator in a Small bathroom that I’m pretty sure I can turn the knob and start and stop the heating during a cycle. I’ll have to try in when it cools off. My new boiler is a lot smaller so I’m cycles will be a lot longer. But should heat the house more evenly once I rebalance it.

John Ruhnke

Efficiency has more to do with the distribution losses. Are the pipes run inside the building envelope? or in a unheated crawl space? Is the radiator recessed in a outside wall? Or standing away from the wall? A radiator cover would decrease energy efficiency as it holds the heat in the enclosed space and raises the temperature at the outside wall. Also how well tuned is the boiler for combustion efficiency? Does the thermostat add unneeded cycles to the boiler? It is more efficient if the boiler runs all the way none stop till the pressuretrol shuts off. Is the surface area of the smaller two pipes bigger or smaller than the larger one pipe? Are the pipes insulated in unconditioned areas? A radiator is more efficient on a inside wall than outside wall. That is because on a inside wall any lost heat through the wall heats up the room on the other side of the wall rather then heating up the outside. Is the boiler room hot? Is there a large fresh air vent pouring cold air into the boiler room? A cold start boiler is more efficient than a boiler banging off a low limit on a aquastat. Does the boiler run all summer to maintain a hot water coil?

Hope this helps.

cgutha

The next question concerns maintenance cost. What does it cost to maintain each system. The above discussion assumes perfectly tuned and maintained systems. What happens when a steam trap goes bad? Do you have to replace all of them? What is their life expectancy? How long will a TRV or air vent last? What happens when condensate pumps go bad? Does the condensate get dumped? Very inefficient.
But side by side in a similar well maintained system, how do the two systems compare in maintenance cost?

PMJ

Two pipe significantly lower depending on type. My Mouat system traps have no moving parts - nothing to fail and still going at 94 years. So no rad vents and no traps to fail. I don't see one pipe beating it on maintenance.

Harry_6

One-pipe was not well liked at the time, judging by all of the competition's claims. They didn't like the hissing and sometimes leaking vents (thus, I suspect giving rise to the "steam is wet heat" delusion), they didn't understand the all-open or all-closed valve requirement (which when ignored may have given rise to their resignation that steam systems make noises), and they didn't like bending over to adjust the valve or that you couldn't throttle it. In the real world, instead of shutting radiators off if the room was overheating (which they usually were - since the radiators were sized for worst-case conditions), the inhabitant just opened the window. Take that fuel efficiency!

Although one-pipe certainly has the advantage of simplicity, the vents fail, the piping is large, and the pressure is relatively high. Fuel has to be burned to displace the system air on every start-up cycle, and it sucks more in constantly, which could increase corrosion. And TRVs, although better than nothing, only work until all the air is vented, and are prohibitively ugly for a historic home.

Since two-pipe residential is usually some version of vapor or vapor-vacuum, it often has the advantage of lower pressure, higher speed filling of the mains (orifices are our friends!) and in some cases few or no moving parts. Also, if a vacuum system, the boiler may run only once a day, while cooking along on steam at below atmospheric the rest of the time. And even if it's a system with thermostatic traps, if orifice valves are used the steam may seldom reach the trap anyway. I've seen many such systems still running with the original traps, because the steam never reaches them and they never cycle. And in cases such as a Mouat, the steam is completely condensed in the radiator, so the returns are stone cold. And since the supply pipes are so much smaller, they radiate less, so there is much less loss in the basement.

My vote is obviously for two-pipe!

Although some of my best friends have one-pipe.

ethicalpaul

That was a cool description, @Harry_6. It makes me want to add a pipe to each of my radiators!

ChrisJ

> @Harry_6 said:
> One-pipe was not well liked at the time, judging by all of the competition's claims. They didn't like the hissing and sometimes leaking vents (thus, I suspect giving rise to the "steam is wet heat" delusion), they didn't understand the all-open or all-closed valve requirement (which when ignored may have given rise to their resignation that steam systems make noises), and they didn't like bending over to adjust the valve or that you couldn't throttle it. In the real world, instead of shutting radiators off if the room was overheating (which they usually were - since the radiators were sized for worst-case conditions), the inhabitant just opened the window. Take that fuel efficiency!
>
> Although one-pipe certainly has the advantage of simplicity, the vents fail, the piping is large, and the pressure is relatively high. Fuel has to be burned to displace the system air on every start-up cycle, and it sucks more in constantly, which could increase corrosion. And TRVs, although better than nothing, only work until all the air is vented, and are prohibitively ugly for a historic home.
>
> Since two-pipe residential is usually some version of vapor or vapor-vacuum, it often has the advantage of lower pressure, higher speed filling of the mains (orifices are our friends!) and in some cases few or no moving parts. Also, if a vacuum system, the boiler may run only once a day, while cooking along on steam at below atmospheric the rest of the time. And even if it's a system with thermostatic traps, if orifice valves are used the steam may seldom reach the trap anyway. I've seen many such systems still running with the original traps, because the steam never reaches them and they never cycle. And in cases such as a Mouat, the steam is completely condensed in the radiator, so the returns are stone cold. And since the supply pipes are so much smaller, they radiate less, so there is much less loss in the basement.
>
> My vote is obviously for two-pipe!
>
> Although some of my best friends have one-pipe.

I just couldn't help but mention, my one pipe system rarely goes above 1/2 an ounce.

tkos115

I gotta admit i'm a bit envious of you folks with 2 pipe steam now.. Hah, however I do like my 1 pipe system. It seems to work well and is pretty efficient. I always grew up thinking steam was a lesser heating system, however after buying my first house with steam I think I would have a hard time going back to anything else.

Randystephensusn20

2 pipe is more efficient because of the simple fact to get the hot water or steam condensate back so you use less makeup water in the system their by decreasing water cost

JUGHNE

Randy, that is probably true with district heating.
We are talking about residential and small comm with the boiler in the building.
The steam system piping should be well designed and the returns clean enough to return the condensate without the addition of makeup water to the boiler. FWIW