Gravity hot water

SeanBeans

Is there any must-dos and must-not-dos when it come to gravity hot water system?

Of course I’m talking about when the old boiler is torn out and the conversion is under way

EBEBRATT-Ed

@DanHolohan talks about it in his book. I think it is in "How Come"

SeanBeans

I see. I’ll have to pick it up. In the meantime I’m looking for some reading materials.

Obviously want to do things the right way

AMservices

Check radiator valves for orifices. Usually found in radiators on upper floors.
Make sure the radiator valves are working so you can balance the flow through the system.
With gravity flow, heat would rise to the top floors first. That's why orifice plates would be used to restrict flow though the radiators on top of the system.
When you add a pump, the water is going to take the path of least resistance. So you will want to restrict the flow through the bottom floors to force the water to the upper floors.

kcopp

Depending on the new boiler will determine a lot.
If its Cast iron oil or gas boiler protection is a must.
If it condensing less so .
Proper near boiler piping is a must.
Don't over pump the system.
Whoever does the swap out should be familiar w/ gravity systems... they can trip you up.

clammy

Remember to keep in mind the volume of water your heating and take care to consider a thermic valve to protect your boiler from prolonged low return temps . Aside from what am services has stated I would suggest the smallest pump you can get .If your system is split into say 2 supplies and 2 return you should install throttling valves to regulate flow on your system loops or add a circuit setter on the supply a much better approach ,Another thing to consider is sludge and magnite I would set up each return so each can be isolated and flushed out with a pump cart if necessary .installing a magnetic dirt separator would also be wise .yet one more thing don’t undersize your expansion figure out your system volume and just because they had a 60 don’t just add another 60 check rads on top floor and see if they are filled w water or do they have air cushion allowing the use of a smaller tank until they bleed out the rest of the air and then you have over pressure and a dripping safety valve have seen and increased tank size and done .i have found that using reducing 90 to decrease your piping sizes works well and instead of reducing coupling due to less sediment sitting in the pipe I usually face them down and add a isolation valve w a purge set up . One small final note if you would like to stop the thermal circulation the occurs when the system has completed its call for heat then install a check on that small system pump .i would as others may suggest is to also pipe primary secondary and be smart add a thermic valve w a140 element piped off the boilers supply into the return also add a few thermometers so you can easily see your systems s and r temps and your boiler temps .i wouldn’t use the low temp circ hold feature to control boiler return temps to drastic swings in boiler temps and uneven heat out to your system loop like a yo yo .most of all of this applies to a standard cast iron boiler not a mod con but in the second case I would make sure the system is very clean before commissioning. I ve found the the formula for near boiler piping to work well everytime I’ve done one which is pipe size divided by two and one size smaller 2 main equals 3/4 sounds tough but never had a issue also a heat lose followed by a radiator survey also puts the piece together nicely .peace and good luck clammy

SeanBeans

Ok thanks a lot guys.

Apparently someone changed every valve on the radiators before they bought the house so I highly doubt they kept orifices.

pecmsg

SeanBeans said:

Ok thanks a lot guys.



Apparently someone changed every valve on the radiators before they bought the house so I highly doubt they kept orifices.

Never A S S U M E what someone else did!

Ironman

pecmsg said:

SeanBeans said:

Ok thanks a lot guys.



Apparently someone changed every valve on the radiators before they bought the house so I highly doubt they kept orifices.

Never A S S U M E what someone else did!

Whether they kept them or not, you will need them in the downstairs rad's for the reason AMservices stated. You can make them from the bottom of coke cans. A 3/8" hole is usually sufficient.

Dirt removal is essential to protect the new boiler. The Ironman header or a Caleffi Sep4 is highly recommended.



It also doesn't hurt to go up one size on the boiler because of all the mass in the system. This will give a quicker response time. One sizer larger that the calculated load that is, not one size larger than the old boiler.

SeanBeans

@clammy @Ironman

So if I had two supply and they were both 2”

I would reduce them back to 3/4?

SeanBeans

Does each supply gets its own pump?

clammy

Sean if both supply and returns are 2 and you have 2 supply and 2 returns ,I would first look at the load each main is suppling and if 3/4 will give each the Btu s they need then yes .I would feed them w 1 and do a reverse return on the piping for either the supply or return does matter as long as first served is the last return if u catch my drift . For what it’s worth I de put a good magnetic dirt separator and a y strainer before it and to really sweeten it up put a circuit setters on the supplies so you can dial in your flow in case one main has far less resistance then the other .if using a cast iron boiler I would install a thermic valve or a I series w outdoor reset and u can protect your boiler and use a reset curve on your supply temp .hope that helps peace and good luck clammy

Ironman

SeanBeans said:

@clammy @Ironman



So if I had two supply and they were both 2”



I would reduce them back to 3/4?

Maybe, but you need to determine how many btus each loop needs and if you need 2 circs or one.

A 3/4' pipe is good for 4 gpm or 40k btus.
A 1" pipe is good for 8 gpm or 80k btus.

EdTheHeaterMan

Primary / secondary is also a good idea. Read @DanHolohan 's
book Primary Secondary Piping made easy
This will involve 2 circulators
The company that purchased my HVAC Business always puts a strainer with a magnet in the return piping to keep debris from getting to the new boiler. THEN Check out the strainer at the first year tune up! If it is like my father (full of crap) at the year tune up, then you need to do it every year. If it is empty, Then put it on the 3 year plan!

Also Pumping Away and other really cool piping designs is another good book

both are available in the Store on this site