Sanity-check your flow rates with the x3 rule

When you’re balancing rads with our FRV valves, here’s an easy way to sanity-check your flow rates. 

• Balancing rads using lockshields is hard and time consuming.
• Badly balanced rads leads to uncomfortable heating, and higher bills.
• A decimal point in the wrong place can thrown everything out.

It’s starting to get cold, and our Frv valves are helping by making it easy to balance rads, especially for heat pump systems. When you’re on site here’s a rule of thumb to check that your sums are okay. 

Just take the output of the rad in kW at the system’s design flow temperature (shown in the rad schedule of whatever heat loss and design software you use), and times it by 3 to get the litres per min. 

So if the output is 500W, then the flow rate should be roughly 0.5 x 3 = 1.5 lt/min at dT5. 

It’s actually 2.87 that you should use for a more accurate result, not 3, but using three is quick and makes it very easy to spot if your sums are okay.

Here are the rules of thumb factors to calculate flow rate at a couple of different dTs. This assumes that there’s no glycol in the system. 

• dT5 x 3 (well, 2.9!)
• dT10 x 1.4
• dT15 x 1
• dT20 x 0.7