Optimal pressure in closed central heating system

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I thought I could ask here. Just did same yearly maintenance on my heating system. System is older with steel pipes and aluminium radiators. I always pressure it to 1.5 bar, but can go to 1.9 bar when hot. Temp range is between 75c to about 90c. So question is what would really be optimal temp and pressure values?.I understand every system vary from each other but some general values would do also.
 

chrisri

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Nebroch hi, Yes I have expansion tank . It's a two story house but system is separated at furnace with two water pumps. Im no expert in this systems so I don't know if this is odd or normal way to build this type of systems. Edit: Furnace is in the seller, so few metres below first apartment.
 
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Down here, they install a head tank with a "sheeps crook" vent higher than the interior ceiling of the highest floor...natural head pressure to counteract the gravity of the internal system...highest radiator plus maybe 5-6 feet. 10m column of water is 1 bar if it helps in the thought process.
 

chrisri

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Different system here, no head tanks whatsoever, only air release valves at top points of pipes on furthest radiators. On a second floor we changed pipes from black iron to copper when renovating couple of years ago. Expansion tank is in the seller next to boiler.
 
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Is the expansion tank water bound? In other words, full of water with no air in tank? We had a system like that years ago. When the system heated up, some water would come out the pressure relief valve. I turned some valves to isolate the expansion tank. Then I drained the tank to let air into the tank. Then I let the system refill the tank. With a pocket of air trapped in the tank, it worked properly.
 

chrisri

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Originally Posted By: Rick in PA
Is the expansion tank water bound? In other words, full of water with no air in tank? We had a system like that years ago. When the system heated up, some water would come out the pressure relief valve. I turned some valves to isolate the expansion tank. Then I drained the tank to let air into the tank. Then I let the system refill the tank. With a pocket of air trapped in the tank, it worked properly.
No, it's normal expansion tank with membrane in the middle. Its half pressured air, half water. When pressure in water system overcome air pressure water expand in tank. It has a air valve so air can be added. What I wanted to know what are optimal temperatures for furnace and what pressure is optimal. Nebroch answered about pressure, what about temp?
 
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hsd

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Optimal water temp would be just hot enough to meet the heating needs of the apartment on a cold day. Higher temp water just wastes energy. Start with 75C and adjust hotter or cooler as needed. Did you install di-electric fittings between the new copper lines and the old iron lines to prevent galvanic corrosion?
 

ffl

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In the U.S. I typically set cast iron radiator temps no higher than 165-170 deg. F. Fin tube radiation (copper) at 180-190 deg. F. In floor radiant( pex tubing ) at 100-110 deg. F.
 
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These days you can buy an electronic aquastat with outdoor reset. It adjusts the boiler temp to the outdoor temp. On a mild day you are not wasting fuel but on a cold day it produces the water temp necessary. This coupled with a low mass boiler and you can achieve some pretty decent fuel savings.
 
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i don't know about 'optimal' but the driving factor is height of the plumbing in the building and keeping dissolved air from coming out of the water when pressure in the piping falls below atmospheric pressure. look it up, i am going from memory which might be incorrect but it's something like for every vertical foot of water the pressure drops 0.5 psi. so for 2 stories or around 20 ft pressure will drop 10 psi. or to get water up 20 ft you will have at least 10 psi at the bottom of the piping because of gravity and the weight/density of water. the requirement is to keep water in hydronic piping under pressure above atmospheric, for one obviously is so that is reaches the highest point in the building so you'll have whatever high pressure at the bottom at the boiler, but also to keep it at least a few psi above atmospheric at the highest point so when hot air stays dissolved and the water moves through the piping quietly. also water under pressure stays liquid at higher pressures. whether going higher pressure in piping helps with hydronic heating, such as 20 psi at some point vs 5 psi, i don't know. from physics does hot water under pressure = more mass = more heat? i don't know. but my guess it's insignificant to matter given the application. and that minor pressure variation should not hurt anything plumbing wise... if you're talking 20 psi vs 120 psi then maybe, if you spring a leak you'll leak more water.
 
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