Hot water heating system pressure setting vs. elevation of area

In Hot water heating system pressure setting does the elevation of the location effect the pressure

  • what should pressure be of hot water system at elevation of 5000 ft.

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stephen reynolds

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In Hot water heating system pressure setting does the elevation of the location effect the pressure setting of the static cold water/
A plumber advised to remove air to set the pressure at 25 psig warm of which it was set at 15 before. Do not have noise of air but could not understand why the elevation of the location would effect this setting and concerned being close to relief of 30 psi
 

Jadnashua

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A pressurized system's setting will need to vary based on two conditions:
- the difference in height from the boiler to the highest point you're pumping the water
- to a much less degree, the elevation

Since water boils at a lower temperature at elevation, that's one reason why you need pressure in the system. Because the water pressure drops about 0.43#/foot of elevation between the boiler and the highest point, you need pressure high enough to overcome the possibility that you could have even lower pressure at the top, allowing even lower boiling points.

A typical 2-story house might have 16' from the boiler to the highest point, or 16*0.43 ~ 7# less at the top than at the bottom. The boiling point of water in an open kettle at your altitude is a bit over 200-degrees. At 5Kft, your 'normal' pressure is about 8#. Throw in the 7# loss at 16', and it would be very close to a vacuum at the top. So, you'd need about 7-psi to keep it from being a vacuum at the top (depending on how many stories your house is), and say another 7psi to bring the pressure up to sea level, and maybe a few more to give you a little margin for error. I don't think you'd need more than 15-20psi... 25psi seems high to me, but I'm not a boiler pro.
 

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Does anyone have suggestion on sizing they flow divider on a hot water system for a kick plate heater which is a maximum of 3 gallons a minute when the Zone tapping into is 9 gallons per minute that is a double O7 pump concerned about backflow and Flow Restriction with the flow divider
 

Dana

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There is no reason to set the system pressure to 25 psi unless the top radiator is 50' above the point of measurement. A typical setup would be set to 3 psi + (0.4335 x height). The additional 3 psi is to guarantee that the pressure top of the system never goes negative relative to atmospheric while pumping, potentially drawing air into the system.

With some water-tube heat exchanger boilers it sometimes takes slightly higher pressure to avoid kettling on the heat exchangers, especially if the primary pump is pumping away from the boiler. (With high head heat exchangers it's generally better to pump toward the boiler for a slightly higher dynamic pressure.)

For most homes 15 psi would be plenty, and it should be set when the system is cool/tepid, not warm/hot.
 
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