Gravity system history.

Mike T., Swampeast MO

Are you certain that multiple rads are served by a single branch line in your system? If each radiator has two pipes leading to it (most typically on either side at the bottom) and no other piping, each rad is most likely served by dedicated supply and return branches. You can verify this by counting the radiators and the branch connections to the mains. If you have the same number of branch connections as radiators on both the supply and return mains, you can be positive that each is fed independently.

That said, it can be extremely difficult to "zone" a gravity system--regardless of the basic piping method used. You'll find that a given main pair serves radiators on multiple floors and in various areas of the house. This makes it nearly impossible to divide the system into logical zones.

"Relatively minor" basement re-piping is a very good way to completely mess up a gravity system! Genuine heating nightmares often begin with just such modifications!

Gravity systems have effectively zero restriction to flow--by modern forced circulation standards it <I>is</I> zero! If your modifications add even small amounts of restriction by modern standards, watch out! Water is lazy! It ALWAYS follows the path of least resistance. When most of the system has zero resistance, it takes little imagination to figure out what will happen in areas where you've added resistance--you'll get comparatively little or no flow. Comparatively little or no flow means comparatively little or no heat!

If you really want to zone and the current piping does "work" with the zones you want to produce, you have two general options:

1) A complete re-pipe. Obviously this is both intrusive and expensive!

2) Thermostatic radiator valves (TRVs). Install TRVs on all of your radiators and each and every space becomes a completely independent zone. Without wiring. Without re-piping. (Well--an inexpensive differential pressure bypass valve must be added near the boiler--but that's generally the only piping change required.) While TRVs DO add restriction, this restriction does not matter. Why? Because TRVs are proportional flow devices--they effectively communicate with each other via the flowing water itself! They will actually bring the total system flow rate down to a level similar to the original gravity operation. While TRVs aren't the cheapest things in the world, they are an absolute bargain considering their effect on such a system.

JohnNY

?

Were gravity systems ever installed as such or are they all converted two-pipe steam systems?

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Brad White_9

Yes, absolutely.

I kind of doubt they were ever converted steam systems because of the disparity in pipe sizes (smaller returns generally are not helpful to gravity flow; even if the returning water is more dense it is not that compact).

Canadians came up with gravity hot water in response to exploding boilers in the US. With the top open (expansion tank in the attic at the high point, pressures were strictly a variable of the height of the system and remained fairly constant at a given elevation.

Wonderful, nice even heat and a default form of OD reset in that the water temperature happens to be lower in mild weather and hotter on cold weather due to frequency of burner cycles. Quiet too as you know. And with millivolt standing pilot systems you would have heat in a power outage.

Mike T., Swampeast MO

They were most certainly installed as gravity water systems from the get-go! They were ALWAYS very expensive. Not only did they require pairs of large piping but the radiators were significantly increased in size compared to steam systems. The nature of gravity circulation also required different piping methods than steam. Many advantages and few disadvantages.

Once circulating pumps became widely available and electricty supplies reliable, forced water systems dominated because the material cost was significantly lower. Once automatic gas and oil burners replaced coal gravity systems became very rare.

DanHolohan

Here you go, John.

Gravity

It pays to wander off the Wall.

[Deleted User]

One pipe gravity...

I saw a 1 pipe gravity system in Denver Colorado that was built in 1905. It used a fitting similar to the OS fitting. Main was about 6", pitched upward at about 1" in 10'. Looked to be an early hot water system when America was still hooked on steam. Wish I'd taken pictures. The house still stands...

Also, as for 2 pipe systems, I agree with Brad, 2 pipe steam would work with a pump, but not as gravity. Too much restriction to flow in the small returns plus friction from the traps.

ME

Mike T., Swampeast MO

Have heard of but never seen those.

Can I test your memory?

Single floor or multiple floors? Big, medium, or small house?

I gather the main stayed big the whole way and looped its way back to the boiler? Return end of the main the high point then nosediving down to the boiler return connection?

Were the supplies always taken off vertically with the returns coming in horizontally? (Most of the multi-floor gravity systems I've seen have the lowest floor done this way but for upper floors both supply and return branches were taken off either at a 45° angle or horizontally.) With such an enormous main and low velocity I'd imagine there'd be quite a bit of temp stratification in the main and that the supply temp at the top wouldn't drop as fast as with a typical one-pipe system--particularly if the returns always came in horizontally with the supplies vertical.

[Deleted User]

Counterflow one pipe...

The hot came off the top, the cool returns cam ein from teh side of the mains, it was a MONSTER house, and multi floor. The system had been bastardized so much it didn't work real well though. Pumps broke up the stratification that it depended on for performance.

The then owner was in dire financial straits and didn't want to hear my recommendations. Not sure what the status of the home is now. It was in need of a total system make over, for heating and plumbing. If memory serves me correctly, I was there for a system inspection for the new buyers...

ME

ttekushan_2

expansion tank filling

In a previous post on another subject I waxed nostalgic about grandma-ma's house with gravity hot water. This is bringing back memories. Gram was only the second owner, the original owner/builder was a Great Lakes shipping captain named Captain Hansen. I understand everyone had better call him "captain." The house was completed in 1901 and sold to my grandmother in 1948. Anyway, grandma was told to flush and refill the heating system once a year. Regardless of the merit of such advice, Grandma did so quite dutifully. And I got to help!

Talk about gravity. The basement window near the fill valve was directly below the vent of the expansion tank that was mounted along side the chimney in the third floor space. My job was to keep the tank filled while grandma bled the radiators starting at the first floor. I'd get yelled at if I had the water shooting across the driveway from that vent!

I remember well how comfy that those huge Triton (US Radiator?) radiators kept the place. Last I heard from someone involved with the local community development corp the house including the boiler is still as it was 18 years ago when I was last inside. Now THAT gives me a warm feeling.

Mike T., Swampeast MO

Thanks for your great memory Mark! Too bad it was bastardized. I LOVE working with gravity systems (converted or not) in essentially original condition. I tried</> once to correct problems in a system with inconsiderate modifications but even at my prices and with my best explanations of why the problems were happening, they chose forced air. The doctor and his drug salesman wife moved out shortly thereafter and built a McMansion. Neighbor told me that they were even less comfortable after the change to forced air. Imagine that...

Mike T., Swampeast MO

HTML fix for the Italics

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EBEBRATT-Ed

20 years ago I replaced a boiler on a simple gravity job. Everyone told me to put in a circ. pump. I said WHY? Since I couldnt get a straght answer I replaced the boiler and left the system as is-job worked -never went back.

Ed

D107

looking at Dan's upfeed system diagram

I notice both floors are fed by same risers. Wouldn't this make later re-zoning (separating 1st and 2nd floors) a very involved re-piping job? I have an old converted gravity and I assumed each radiator had its own supply and return riser--which is how I thought they were able to easily make it into two zones by some relatively minor basement repiping.

Thanks,

David

Constantin

Looks like it didn't work...

... I think you'll have to edit your message to insert the missing <i>...

Mike T., Swampeast MO

Wasn't at the right computer--only get the edit option from the computer that posted the message. At least it stopped all following posts from being in italics.

D107

Thank Mike for posting the detailed reply; I should

have made clear my system was converted from gravity years ago, and zoned successfully into 2fl/1st fl. Unfortunately they sealed the basement ceiling so I can't see much of risers and mains but it seems clear every rad has its own supply and return otherwise how could they zone without the massive job you mention--which I know they didn't do.

My layman guess is that since many old gravities were two supply and two return lines, they simply took one supply and return for 1st fl, and one set for 2nd. (in the original gravity system I assume these two sets were divided between, let's say, the north and east sides (both floors) and south and west sides (both floors). (Actually, without being able to see basement piping I don't know if the rad returns go back to a separate return manifold, or back to the supply main en route to the other rads.)

It seems to me that the upfeed system in Dan's diagram would be more economical --with multiple rads feeding off a single riser--than what I have where there has to be alot of heat and time lost for every rad to be served individually by all that piping. I guess that this was done due to the house design and where a rad could be placed in the various rooms near the windows and the rad sizes.

All of which leads me to think that the primary benefit to zoning is to be able to isolate one zone for repair/draining while leaving the other alone. For heating purposes not sure it's that important to separate 1st and 2nd floors. (Though I admit on weekends I stagger the downstairs thermostat to come on an hour later since we sleep later.) Of course if you have an porch extension on a cold slab or other room that you rarely occupy that's certainly a candidate for zoning to save heating costs.

I am in awe of the old gravity system and the genius that it represented at the time, and with the help of some pros I've contacted through the Wall and Dan's books, I've been able to figure out how most of it worked. It's taken more time than I anticipated to wrap my mind around this, but I've enjoyed unraveling the mystery. Wife, who's always cold at any temperature, surprisingly does not share my fascination.

Thanks again,

David

Mike T., Swampeast MO

Crap! I can't even fix it from the original location because an employee constantly clears everything to cover his tracks. Why did I ever tell him how to do that? At least he learns quickly...

Steamhead (in transit)

You're right

US Radiator made the Triton column rads. I see many of these beauties around Baltimore.

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Weezbo

i have made a run on some pics for you...

gotta boogie at the moment...old style gravity boiler ,outdoor boiler temp control,and some associated pieces.*~/:)