Hot Water System Pressure Question

Brad White

Granted the term "story" can be subjective, but for a house I figure ten feet. (My house has 9 foot ceilings and about a foot of structure between, close enough).

It really is the height from the gauge to the highest point of the system plus 4 to 5 PSIG to top it off.

Let's say your 2-story house (2-storey if you are in Canada or Britain), has 10 feet floor to floor and say 8-feet from basement slab to first floor level. Thus your total height from basement slab (El. 0'-0") to second floor would be 18 feet (8+10)= El. 18'-0"

Let's also say that your boiler gauge is five feet above the basement slab at datum El. 5'-0".

Measure vertically from that point (five feet above the basement floor) to the high point of the system. Say that this high point is a standing cast iron radiator on the second floor and is 38 inches high, call it three feet or datum El. 21'-0".

Your total system height is 16'-0" (21'-0" top of radiator down to 5'-0" gauge elevation).

Multiply 16 feet by 0.433 to get PSI gauge pressure and add the 4 to 5 pounds topping off pressure.

16 x 0.433 = 6.928 call it 7.0 lbs. plus say five and make it a nice even 12.0 PSI cold fill pressure.

Basically, a 12 PSI fill pressure is an excellent reference point for any 2-story house. Add 4.33 call it 5 PSI per floor above that. I default to 18 PSI for a 3-story house.

Got you covered.

Al Roethlisberger

Hot Water System Pressure Question


I've read the general rules of thumb on this topic, but after giving it some thought, still have a question.

I have a "2 story" house, however, the boiler is in the full height finished basement, and the overhead gravity system carries all the hot water up into the attic above the 2nd floor. So the rules of PSI per floor had me slightly perplexed as how they apply to my home/system.

So here's the question: With my boiler in the basement, 2 stories above, and the piping/riser continuing into the attic immediately above the 2nd floor ceiling, what PSI should I expect as normal for a hot water heating system?

Most equipment and recommendations seem to put hot water systems at 30 psi max, so before I bought relief valves, etc, I wanted to know what PSI I should consider normal for my system.

Thanks
Al

al_roethlisberger@yahoo.com

Al Roethlisberger

THANKS!


Excellent reference Brad. Thanks!

Al