Gravity Hot Water Heating

CJRS

some of the old gravity systems were OPEN systems where te expansion came out of a pipe at the roof and sometimes it was piped down along the side of a house. If you simply overfill your system, it will fill that expansion tank and overflow. That may be what you are seeing. There are some great reading articles on diff types of gravity installs from the 1890's - 1900's at www.oldhouseweb.com you may want to check it out.

Bill Lamp

Gravity Hot Water Heating System

I have a gravity hot water heating system in a house built in 1939. Does anyone have experiences replacing the boiler in a gravity system while maintaining the gravity distribution system? Is there a current boiler manufacturer that has a boiler configured for a gravity system, or would a new boiler have to de-coupled from the gravity distribution system?

Thanks for your help.

Constantin

Multiple installers here have converted gravity systems...

... perhaps this bump of the message up to the top will help put your question in front of them again.

My recollection seems to indicate that sizing the pump right is very important, as gravity systems have very little pressure drop, so they need much smaller circulators than systems with smaller pipe diameters.

I have read multiple posts from installers here that have successfully married small boilers (including modulating/condensing boilers) to gravity system pipes, so you have a wide range of boiler options you can consider. Perhaps doing a search here with 'gravity' as a keyword may also point you in the right direction.

Mike T., Swampeast MO

I've looked and have not been able to find any modern boiler with either tappings of sufficient size and sufficient water quantity to directly drive a gravity system. Have had some "imagineering" discussions with others on how to use a modern boiler on a true gravity system, but not sure if the ideas would work...

It's probably time to highly consider the change to florced flow.

Uni R

P-S

Has anyone ever just piped one primary-secondary with a circulator for the boiler loop but leaving the heating loop as strictly gravity fed?

CJRS

yes, you can use your gravity system

There are many things that need to be taken into consideration but for the most part you can connect a new boiler to exisitng gravity system. How do I know?..I have one. It works very well and rather efficiently for a system that I didnt have to totally re-do. There are several factors to know such as the approx water capacity of your system (all radiators and piping) and the expected BTUH of the system. An experienced boiler installer is the way to go and spare no time in finding right one by asking quesitons about their qualifications. You can contact contractors directly or get recommendations from local mechanical engineering firms in yoru area who know qualified installers.
Providing that the piping is in decent shape, you should be able to use the system but will hve to reduce the piping for the return and supply (usuall to 1" or 3/4" pipe) may sound small but its not since the new boiler will most likely have a circ pump on the system. My system, I recently discovered, uses a circ pump on the return side as to not restrict flow to the rads from the boiler when the burner is not operating but the hot water flow is maintained by conveciton current. (some boiler piping may require a by pass of the pump to allow this to happen) The newer the boilers, most have a conservative reservior, the older ones have a larger capacity that coincided with the over-sizing design methods of the past gravity systems. There are recommended controls for todays systems that also will improve efficiency such as step controls for the circ pump and burner to run simultaniously or let the circ [pump run seperately using the reserve hot water that is stored in a large capacity boiler. A good contractor can explain and recommend what is best for your system based on your home's needs. Good Luck!

Lost

gravity radiator problems

I have a two flat that has two different boilers in the basement that heat each floor separately. The first floor's water radiators work great, no issues. The second floors radiator do not work well at all. The bottom of radiators are hot but the tops are warm at best. I tried to bleed the air out but little air comes out. I've located the expansion tanks but they do not have a water level gage on them. I decided to simply add more water into the second floor system but it did nothing to the radiators. To my surprise though i found two pipes in a different location of the basement. Both pipes seemed to be cut at one time. One of which has a started slow trickle of water flowing from it. I can only assume that the leak is due to adding water into the system. It was not leaking before. I'm just confused as to what these pipes would be. Can this be the remains of a Heat Generator? Did the deadmen typically install radiator in basements?

Mike T., Swampeast MO

What pressure reading do you get on the boiler gauge?

Lost

Gravity Hot Water Heating

1st Floor boiler: 7 psi & 35ft altitude
2nd floor boiler: 5 psi & 36ft altitude

coreys

Gravity

Thinking out of the box;

A crazy 'hybrid' idea for retaining gravity flow might be a 'big tank approach'.

The concept here is that you would force-circulate the water through the boiler into and out of a big tank. This is essentially a 'primary loop', then gravity would take over from there for the 'secondary loop'.

This solves the problem of getting enough flow through the boiler. You could even use a low mass modulating boiler.

The difficulty might be finding a tank with large enough fittings. I am not sure if adapting the fittings down would destroy the gravity flow in this case or not. Experts here will know that stuff.

Of course the main question will be; why retain gravity flow in the first place?

coreys

Gravity

Thinking out of the box;

A crazy 'hybrid' idea for retaining gravity flow might be a 'big tank approach'.

The concept here is that you would force-circulate the water through the boiler into and out of a big tank. This is essentially a 'primary loop', then gravity would take over from there for the 'secondary loop'.

This solves the problem of getting enough flow through the boiler. You could even use a low mass modulating boiler.

The difficulty might be finding a tank with large enough fittings. I am not sure if adapting the fittings down would destroy the gravity flow in this case or not. Experts here will know that stuff.

Of course the main question will be; why retain gravity flow in hte first place?

Dave_4

The altitude needle is fixed and indicates where you want the psi (pressure) needle to be located.

5 psi will only lift water about 11 feet. Presuming the pressure gauge is working, that's why you have almost no heat in the 2nd floor--no water in the radiators!

Dave_4

That's roughly the idea another Wallie and I thought about.

Also considered a large diameter (say 8" or larger) black steel pipe five or six feet tall. Then you could weld in your own tappings...

Must agree on the "why bother" unless electricity is highly erratic, unavailable or undesired.

Gene_2

Gravity Hot Water Heating

Thanks for the information! What i can not understand is that as i add water to the 2nd floor system, water begins to stream out of a 1" diameter pipe. This pipe is located at the back of the building almost in line with expansion tank. The boiler on the other hand is very close to the center of the building. There are actually two pipes a 2" diameter and 1" diameter pipe coming directly out of the basement ceiling. I'm wondering if these two pipes were connect at some time and is the reason water will not raise to the 2nd floor radiators. Any trouble shooting advise?

Dave_4

Can you trace the pipes?

If the pipe that streams water is some sort of overflow it might be possible that there was an overfill or overheat condition in the past and water is trapped in some horizontal piping. Did you stop filling as soon as you saw water? If so, you might try a bucket and filling for a while to see if the water flow stops after a short period.

Surely you've opened the radiator air bleeders when you're filling...

Lost

Gravity Hot Water Heating

Unfortunately i can not trace the pipe. As a matter of fact these particular pipes are not even near the boiler. If it wasn't for the sound of the water hitting the floor i probably would not of known it was leaking.

I did have the air bleeders open while i filled. As a matter of fact i filled the system for about 15 min. The stream of water began a short time after filling. Actually water is still slowly flowing and it's been three days since I added water to the system.

How can i tell if this is an open or closed system?

Unknown

Mike , a few manufacturers

make gas and oil boilers for steam or hot water , and have good sized tappings for gravity hot water . I used a Peerless JOT4 on a gravity system , and the homeowner wanted to keep it gravity . We connected both 2 inch boiler tappings into the 3 inch main , and reduced the 3 inch return to 2 inch . I was amazed at how fast the cast iron rads heated up . Not sure how the boiler handled the prolonged low return temps though - we didn't install a bypass back then , maybe 15 years ago .

drahcir

gravity heat

I am installing a wood fire hot water boiler and have collected 8 cast iron radiators. I want to create a system with the cast iron radiators and the boiler. The boiler will be in the basement and all of the radiators as well. I was thinking of putting one radiator on the first floor to create a gravity flow from the boiler to the rest of the radiators in the basement. Would that work? Since at some point we may loose power and not have heat.

RHall

Re: gravity heat

If your radiators are going to be on the same story as the boiler (e.g. basement), you'll probably want to think about an overhead-distribution gravity system. There's a main riser coming out of the boiler to the basement ceiling: the water goes up first, then through pipes running along the ceiling, then down to the radiators, through the radiators and continuing down the return lines. This is basically the system used in our old carriage house (around the turn of the century) (stable, garage, and carriage room) with wall-hung radiators, although the heating system isn't currently in operation. This system was also called "first-class" gravity system.