Water & plumbing systems
Working out the water a pipe holds, its weight and fill time — for plumbing, irrigation, pools and hydronic loops.
Why this topic matters
Most plumbing and hydronic questions come down to how much water a run holds, what it weighs, and how long it takes to move. Those three follow directly from the internal volume: water is about 8.34 lb per US gallon or 1 kg per litre, and fill or drain time is simply volume divided by flow rate. The tools below cover the water content of a run, the per-foot capacity used for quick field estimates, the fill and flush time from a flow rate, and the specific materials — PVC, copper, PEX — that carry domestic and heating water. Totalled across a system, the same volume feeds expansion-tank sizing, glycol charges and the make-up water a leak will call for.
On heating systems in particular, the pipe itself can hold a surprising share of the water — long radiant loops of small-bore PEX add up — so totalling every run matters before you size an expansion tank or mix a glycol charge. The system-volume guide brings the pipe total and the equipment content together and turns them into a tank size.
The flow tools close the loop for commissioning: once you know the water a system holds, a flow rate turns that volume into a fill, drain or flush time you can schedule, and the chlorination or glycol dose follows directly from the same gallons or litres. Water work is where volume, weight, time and dosing all meet, which is why these tools are grouped together.
Tools & guides tagged “Water & plumbing systems”
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How do I find the water in a whole plumbing system?
Total the volume of each pipe run (using the true bore) and add the boiler, emitter and tank content from their datasheets. The system-volume guide walks through it.
How much does the water in a pipe weigh?
About 8.34 lb per US gallon, or 1 kg per litre. A full 100-foot run of 4-inch pipe holds roughly 66 gallons — around 550 lb.
How long will a pipe take to fill or drain?
Divide the volume by the flow rate. Enter a flow rate on the flow-rate tool and it returns the fill or drain time; a 500-foot 2-inch run at 10 GPM fills in roughly nine minutes.