There is situations where a Hot Water meter could clock in reverse, why? The below will outline a few things that could be happening and what it can do to the affect the readings on the Hot Water meter.
- The water meter is installed in reverse. Common for normal turbine meters. Although if it does clock upwards and go backwards slowly this would more likely be the below issues...
- Thermal contraction of cooling hot-water pipes can pull water backward and slowly spin the meter in reverse.
- Natural convection can create a small circulating loop that moves water backward when the system isn’t flowing.
- A missing or leaking check valve can allow reverse flow through the hot-water line. Also known as a non return valve.
- Pressure fluctuations in the plumbing (like cold water use elsewhere) can temporarily push water backward.
A meter without anti-reverse protection may register even tiny back-and-forth pipe movements as reverse rotation.
What does this mean for billing?
When a turbine hot-water meter spins backward, even slowly, it effectively subtracts from the total recorded usage, meaning the resident is billed for less water than they actually consume. Over time, this can result in undercharging, which not only affects revenue for the building or utility but also skews consumption data used for managing utilities or detecting leaks.
What can fix this issue?
It is always recommended to fix the problem on the hot water supplying system itself where possible. Although it might not always be the case, here is a few ways to fix the problem of a hot water meter going backwards.
Install or replace a check valve on the hot-water outlet or recirculation line to stop reverse flow. Also known as a non return valve for some.
Add a thermal expansion tank to absorb pressure changes that cause backflow.
Insulate the hot-water pipes to reduce cooling and prevent reverse convection currents.
Install a heat trap (or heat-trap nipples) on the water heater to block thermosiphon flow.
Replace the meter with one that has anti-reverse features if accurate metering is required even with tiny flow fluctuations.