Vintage 1909 Gravity Hot Water Heating System

Attic expansion tank is a big deal in my opinion. Air ends up there so no messing with individual bleeds?

The open to atmosphere expansion tank is either a horizontal steel saddle tank or a vertical steel tank. The hot water riser pipe feeds hot water to the open to atmosphere expansion tank.

If the attic is uninsulated or poorly insulated you use a U piping method connected to the bottom tapping of the vertical steel expansion tank that rests on planks set on the trusses where the piping is set up with the riser on the top floor reaching the attic space and then it is met with an elbow that connects with a short nipple that is connected to a T.

The is Tee connected to a short nipple riser that is threaded into a union or the base of the steel expansion tank resting on the planks.

A short nipple is connected to the drop pipe with a second elbow and then to the short drop pipe to the take offs feeding the radiators on the top floor and then the drop pipes on the top floor radiators to feed the lower floor radiators and then drain back to the boiler sump.

Both the vertical and horizontal open to air expansion tank are protected with either a riser pipe passing through the roof which has an elbow and short nipple and then a second elbow with a screen in it to allow excess water to rise up and fall on the roof and into the rain gutter.

In this method of using a saddle mounted steel expansion tank you would connect the riser to one of the tapping's in the side of the tank using just the riser pipe a union and short nipple and connect the drop pipe to the closest side tapping using short nipples and union to allow the hot water to move quickly to the drop pipe.

The vent pipe riser would be connected to the one of the tanks opposing tapping's and piped through the roof where it would use an elbow, a short nipple, a second elbow and then a screen to keep vermin out of the pipe; you would fill the tank and wait for the water to come out of the roof vent riser and then stop filling it.

With either tank mounting method you could pipe a drain pipe to the basement floor drain or a laundry sink and simply open the fill valve and wait for the excess water to drain from the tank to the floor drain or the laundry sink.

You would want to wrap the tank and piping in insulation if there is no insulation in the attic.

Mr. Holohan explains this in great detail and has illustrations of it in his book Classic Hydronics. If you buy this book he will show you how this method of piping is done with a bottom fed gravity system or a top fed gravity hot water system which eliminates air bubbles and slugs of air in the piping.

Either of the top fed or bottom fed gravity hot water piping methods will provide slow even heat for you using gravity with no circulators. Mr. Holohan shows you how to do this in his book Classic Hydronics and his illustrations also show how to plumb the radiators with monoflow tees and shut off valves to regulate the amount of heat in a room or open space.

As long as you read Classic hydronics you will understand that the gravity hot water heat method acts like a conveyor belt and reading more about how the top fed method of gravity hot water heating eliminates the need to bleed air from the radiators as there is no air in the water because the water fills the radiators from the top down and as the system fills it allows the air in the system to vent through the open to atmosphere steel expansion tank and out the roof vent pipe.

Attic expansion tanks have an open vent to the atmosphere, at least in residential systems.

What is great about a gravity hot water heating system is you can have a circulator pushing hot water up a multistory system to a pneumatic storage tank open to atmosphere with a float switch and have simple gravity hot water heat for the multistory building.

I fully understand that.

I am just mentioning gravity can be used to its advantage in tall buildings over three stories tall by using a small centrifugal pump to push the water up into a nurse tank in a top floor to allow the hot water to be used in a top fed method.

love the attic utility sink next to expansion tank. Love old gravity systems. Simplicity and function. Most of our older gravity systems had Roberts Gordon atmospheric conversion burners on them. Still think I have one of the last sets of ceramic diffuser plates anywhere around here. Pretty interesting to see what was, what is and what will be.