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# Question on pressure

Member Posts: 406
the biggest Btu's of steam are when it changes state from steam to water, (gas to liquid) That is where the (970 Btu's per pound of steam (mass & or weight)leaves its collective mark. That occurs easily at the vapor stage. And that is why the low pressure systems work so very well. To Heat the Steam(gas) beyound that is not all that great. Oh there is some more btu present but it is not a much as the change of state. plus you have to cool down that to the change of state phase before you can recover the major portion of heat. Radiators are hot enough at 212* without going to 350* just for the hell of it. JMHO bigugh Not to mention the heat that will go up the chimney at the higher pressure!

• Member Posts: 398
Pressure

Ok I know that pressure is the bad word in steam, but for discussion sake, if your boiler were to cycle on pressure, and lets say for arguement sake alot of pressure 4 to 5 lbs would the extra heat carried from the pressurized steam heat a room faster? I use a pressure cooker as an example. steam at 5psi is hotter than steam at 1psi. Would the time that the boiler is in "off from pressure mode" save fuel? I use a car coasting down hill as an example here. I would think that with a larger head of hotter steam, your cycle time would be longer and you would get a longer "down hill coasting" effect. I would think that the amount of fuel used to go from 1 psi to 5 psi in one cycle would be less than having to re start each time from a cool boiler. What do you think?
• Member Posts: 443
One...

... of the big reasons for the lower pressures is that you can have the condensate "stack up" in the returns, and use gravity to push it back into a running boiler. At 2 PSIG, you'll need about 5 vertical feet of condensate over the boiler water line to get the condensate into the boiler. At 4 PSIG, now you'll need about 10 feet. This will typically flood the 1st floor rads. Some systems use higher pressure steam for a variety of perfectly good reasons, but with little low pressure heating boilers, it just means you now need to buy and run a pump to get condensate back into the boiler.
• Member Posts: 398

So yes there is always more to it. Thanks for the great answers.
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