gravity heating questions

stelradCoal

Hello,



I own and live in a house in CT. Its good sized and has a gravity heating system. My wife bought the house while I was in Iraq the first time in 03 and I came home and used the web to figure out I had a gravity system and the magic of how it works. The system works well, radiators get hot allover, and there is no pump at present.



In the basement I have an enormous boiler that heats the water quite well (its about 300k btu or so). I'm guessing the boiler is circa 1960 or so. When I moved in there was also a 1985 hand fired coal boiler (120k btu or so) hooked up next to the main boiler. It had a cold line running from a tee off the line running to the bottom of the main boiler and a hot return going into one of the two hot water risers. Actually it was plumbed into the line off the riser that used to go to an under the floor radiator that used outside air and had been disconnected.



So after paying a few of the enormous gas bills that went with the enormous gas boiler I decided to try my hand at shoveling coal. By and large all went well. I did have some problems with warming the rooms that were off the other hot riser from the main boiler, and on the absolute coldest of days the coal boiler was not quite enough and the temp would fall in the house to the low to mid 60's without constant tending. But overall a good way of saving a few bucks. Oh the only other issue is I had to tend it every morning and night or else.



So last year as I went to fire the old boiler up again I discovered a crack. Long story short I decided to upgrade the coal boiler with another coal boiler but this time auger fed so I don't have to do the coal shoveling (nor my wife). I'm in the Army Reserves so I can be gone for a weekend during the winter and shoveling coal to keep the boiler going was a real pain for her. So anyhow last spring I picked up this new/used/rebuilt boiler and now want to add it in to the system, but I don't want to add it in where the old boiler was because of access to the coal.



So, I have a chimney on the other side of the basement and want to put the add on boiler there. Questions I have are:



What about adding it in as a gravity boiler from that location?

Could I just connect piping from the locations the current coal add on is to the new boiler?

Would the new boiler operate properly if I lifted the cold side of the line up to the ceiling so it was not running across the floor?

Would I need check valves then?

What other options do I have?

Should I run the coal boiler separate through a heat exchanger that could be located right at the end of the cold return before the boiler?

Would the gravity system still work then?



OK so the end goal here would be to have the add on coal boiler connected so that it could run without interfering with the operation of the gravity system so that if the coal system were shut off the gas boiler would work as it always has.



I have a few more months to think and plan for this as I am back here in Iraq, but I don't think my wife is going to buy another house before I get home this time :-)



Thanks for any advice.



Jay

Jamie Hall

Thank you!

and having said that -- no politics -- some thoughts on your questions:

What about adding it in as a gravity boiler from that location?

Probably should be OK.







Could I just connect piping from the locations the current coal add on is to the new boiler?



Could I just connect piping from the locations the current coal add on is to the new boiler?

Yes, but you will need nice big pipes.  Gravity circulation depends on good sized pipe.  Also, insulate them thororoughly, and check and double check the pitch.







Would the new boiler operate properly if I lifted the cold side of the line up to the ceiling so it was not running across the floor?



Would the new boiler operate properly if I lifted the cold side of the line up to the ceiling so it was not running across the floor?

Um.  Well, I expect so.  But that depends on how you hook it into the existing line.  It would probably not run properly if you had to go up to the line across the ceiling, then across, then down.  If you could hook into the returns at the ceiling, and go across steadily pitched down, and then drop, it should be OK.





Would I need check valves then?

Shouldn't...





What other options do I have?

You might consider, since you are using an auger anyway, adding a pump for circulation from the new boiler.  That would give you positive circulation, and you could use smaller pipes from the existing boilers to the new boiler.  If you did that, you might want to use check valves on the piping to the old boilers, to prevent short circuiting through them.





Should I run the coal boiler separate through a heat exchanger that could be located right at the end of the cold return before the boiler?

I wouldn't bother.





Would the gravity system still work then?

Robert_25

Coal Setup

How much distance would be between the two boilers if you installed the coal unit on the other side of the basement?  Gravity circulation requires large piping, and this could get expensive fast.  You might want to consider forced circulation as part of the project. 

What make and model coal boiler did you buy?  EFM?  Axeman Anderson?

stelradCoal

coal-o-matic

My concern with the pump is that it would screw up the gravity system potentially?



The other add on boiler was connected via 1 1/2 in & 1 1/4 in pipe - they were short runs - maybe 4 - 8 feet and they tee'd into much larger runs.  This new run would be a longer - probably 20 foot or so - run. 



If I were to pump the water from the add on to the main boiler - do you think it would be possible to plumb it in and out so that it acted as a "heater" for the main boiler water without disturbing the normal gravity flow?



The boiler is a coal-o-matic.  Not a very common one, but looks like a pretty nice / simple design.  I'll tell what I really think when I have her hooked up and burning!



And thanks for your support we appreciate it - no matter what your politics are!

Jamie Hall

Shouldn't be a problem

as far as keeping the gravity system.  You will need one check valve either on the inlet or outlet to keep the it from short circuiting, but that shouldn't be a problem.  If you go with a small pump you can hook it in with relatively small pipes.



I don't think I would include the existing gravity boiler in the loop; too much water to keep hot.  That's a detail -- and you sound handy.

stelradCoal

pumping in circles

What I am thinking is, what if I took cold water from the bottom of the boiler, or right before the return enters the bottom of the gas boiler, and I returned the water to the top or near top of the gas boiler?



If I use a pump, would it more or less just heat that volume of water in the gas boiler main body and then that mass of water would start the gravity heating cycle? I'm just thinking that if you plumb it that way it should act on that water in the gas boiler tank rather than inducing a flow through the gravity system?