Home hot water heat system pressure is too low?

[monk9]

I've been browsing the advice found here regarding draining x-tank in order to prevent the overpressure valve from discharging. Found my tank was full, so followed the advice here and drained it. Before that, the pressure was varying from ~12 to 30 psi. (It vents at 30.) Now with mostly empty tank, the psi is between 5 to 10 per cycle. Doesn't seem to be any air in the rest of the system. But it does seem to heat more slowly now.

Questions are: For my split level home, is 5-10psi okay? If not, what should it be and how can I increase it?

Thanks in advance for any advice offered.

 

[quark]

It is difficult to say anything without knowing details about flowrate, pipe size and heating system.

Your system may be starving. Low flowrates result in low pressure drops and slow heating rates. But if the earlier pressure swing is between 12-30psi, you may be close to the required pressure(I assume it to be 12). You shouldn't totally drain the tank but should keep enough empty space for the expansion of water at the maximum operating temperature.

Specific volume of water corresponding to a saturation condition of 12psig(26.7 psia) pressure is 0.0169504ft³/lb and at 30psig(44.7psia) it is 0.0172053ft³/lb. This means for every lb of water in your system, you should have 0.0002549ft³ free space.

Regards,

 

[TBP]

Is it a plain steel tank, or bladder tank? If it's a bladder tank, the air pressure needs to adjusted by adding or removing air through the stem. (Looks just like the one on a tire.) The fill pressure of your system will be however much pressure you need to get water to the top of your system, plus 4 or 5 PSI to make sure it's full. The air pressure needs to match this cold pressure, and must be checked with the tank disconnected from the system. If it's an old tank, the bladder may be shot. If it's a plain steel tank, it'll need an Airtrol fitting in the bottom, where it connects to the system piping. If you don't have this fitting, the air in the tank will gradually dissolve in the water, and get kicked-out by the air separator. This is why this style of tank can flood over a heating season or two.

 

[hockeyman]

I read your delema if you have a multi level house look at aprox.6 psig per floor also if you have a gas fired boiler make sure it's tubes are clean(heat exchanger)and burner orifices let me know

 

[ChasBean1]

I'm not a home heating expert, but here I go, for the sake of pontification...

12-30 psi swing means your "x" tank aint "x"ing. You drained the thing and found the heat-up rate to be low. It means you shifted the bubble from the pressurizer to the reactor.

If you live anywhere near Three Mile Island, PA, please evacuate. Otherwise, get a new bladder tank.

 

[lilliput1]

Is there a pressure regulating valve to the city water makeup line to the heating water loop? Its setpoint must match the pressure on the expansion tank. If there is none then the pressure on the expansion tank must match the city water pressure. The relief valve should be set at a pressure such that no portion of the system would see the maximum allowable operating pressure of the equipment or piping. This could be 100-125 psig max. If the city water is at 50 psig, the expansion tank expansion volume should be such that it can accept the expanded volume without the system pressure exceeding the relief valve pressure.
If there is a pressure regulating valve and the elevation from the expansion tank elevation to the highest point in the piping is 15', then the minimum fill pressure seting for the PRV & expansion tank in psig = (62.34/144) x (15+5) = 8.7 psig. Where 62.34 is lb water/cubic ft. The larger the pressure difference between the expansion tank fill pressure & the relief valve setting, the less the volume requirement for the expansion tank.

 

[lilliput1]

Oh check the maximum operating pressure of the boiler. I do remember seeing one rated at only 50 psig maximum pressure.