Heat Meter Installation and Replacement: Step-by-Step Guide

Who Installs a Heat Meter?

Installation and replacement are a job for a qualified installer or a metering company. Honeywell and ZENNER require installation to be carried out by qualified personnel in accordance with the manual. Three points need attention during the work:

• Pressure and hot water: The valves before and after the meter are closed and the line is depressurized. ZENNER warns that hot water escaping during removal can cause scalding.
• Electrical: Apartment-type meters run on batteries; for M-Bus connections, electrical installation rules apply.
• Seal: At the end of the installation, the temperature sensor on the opposite line and the meter are sealed; the factory seals are not touched. According to Calmet's technical document, a meter with a broken seal cannot be used as a basis for billing. For re-verification and stamping, see our Heat Meter Re-verification and Calibration page.

Preparation Before Installation

Size, body length (L) and connection thread

When replacing, the most practical approach is to choose a model with the same size (DN), the same body length (L) and the same connection thread as the meter being removed; then no changes to the installation are needed. L is the length between the two connection ends of the body; measure the length of the existing meter before removing it. The same size can come in different lengths: the DN20 version of the CEM CM-HR is 130 or 190 mm long, while the Minol Zenner C5 IUF DN25 on our site is 260 mm. On the threaded models on our site, the body thread is one step larger than the pipe size and the meter is connected to the installation with couplings: the body of the Honeywell EW700 DN20 is G1”, and its coupling fits a ¾” pipe. Couplings, gaskets and sensor fittings are in our heat meter spare parts category.

Valves, strainer and flushing the installation

• Service valves: Honeywell, CEM, Calmet and ZENNER require or recommend a valve before and after the meter.
• Strainer: Honeywell recommends a strainer on the inlet side of the meter; CEM states that the flow drops markedly when the filter becomes dirty. Calmet says that a strainer is not needed under normal conditions, but should be fitted before the meter if the water is dirty. In impeller-type mechanical heat meters, the filter is even more important because sediment can hinder the impeller's rotation.
• Flushing: All manufacturers whose manuals we reviewed require the pipes to be flushed before the meter is installed. Honeywell also states that chemicals used to clean the installation can damage the flow sensor.

Installation Point: Supply Line or Return Line?

A heat meter must be configured for the line on which it is installed. Which line depends on the model: some models are installed only on the return line, others on the supply or return line. On ZENNER meters the correct line is written on the label; on Calmet and Danfoss it is also shown on the display. Information from the manufacturer documents for the models on our site:

The Turkish-language installation instructions for the Honeywell EW700 require at least 10×DN of straight pipe before the meter and at least 5×DN after it; the English data sheet, however, says it is not needed. If the installation allows, meeting this condition is the more cautious approach. Whichever model is installed, the following rules apply to all:

• Flow direction: The arrow on the body must point in the direction of water flow. CEM states that a meter installed in reverse cannot measure the flow.
• Air: The meter is not installed at the highest point of the system, because air collects there (ZENNER, Honeywell). CEM requires that in a U-shaped installation the meter sits below the pipe level.
• Vertical pipe: For vertical installation, CEM requires choosing the pipe in which the flow is upward; in a pipe with downward flow, the water cannot fill the pipe completely. Honeywell also recommends this.
• Pump and valves: Calmet requires that the flow sensor is not placed immediately before or after a pump or immediately after a valve (except fully open shut-off valves); Honeywell requires a distance of 10×DN from a pump or motorized valve.

Step-by-Step Heat Meter Installation

The common sequence in the manufacturers' installation instructions is as follows:

1. Close the valves before and after the meter and depressurize the line.
2. Remove the old meter or spacer; clean the gasket surfaces and check them for damage.
3. Use new, intact gaskets. ZENNER does not allow hemp or similar materials; Calmet requires original gaskets and fittings.
4. Position the meter so that the arrow on the body points in the direction of flow. The meter must not be under stress (Calmet, Danfoss); if the pipe axes are misaligned, do not force the meter; correct the installation.
5. Tighten the couplings with two wrenches; do not use the calculator unit as a handle (Honeywell, CEM). Honeywell specifies a torque of 10–20 Nm for the couplings.
6. Turn the calculator unit so that the display can be read, or move it to the wall if necessary.
7. Install the temperature sensor on the opposite line and seal it.
8. Open the valves slowly and carry out the commissioning checks.

Installing the Temperature Sensors

A heat meter has two temperature sensors. On Danfoss, Calmet and CEM, one comes factory-fitted in the flow sensor body; the other is installed on the opposite line during installation. ZENNER prefers the two sensors to be installed symmetrically, i.e. with the same type of ball valve on both lines; if the sensor came fitted in the flow sensor, it is not removed. In heating, the sensor with the red label measures the supply (hot) line and the sensor with the blue label the return (cold) line. In cooling meters, the color scheme varies by brand.

• Ball valve: The second sensor is usually installed in a ball valve with a sensor port, immersed in the water. CEM's steps: remove the plug from the valve, place the O-ring in the port, insert and tighten the sensor and seal it.
• Sensor pocket: Honeywell allows the sensors to be installed directly in the flow for DN15–DN20, and directly or in a pocket for DN25–DN40; both sensors are installed the same way. Calmet requires that if a pocket is used, both sensors are placed in pockets.
• Tightening: ZENNER specifies 3–5 Nm, Danfoss 12 ± 2 Nm; Calmet requires the plastic sensor coupling to be tightened by hand without tools.
• Cable: Sensor cables must not be shortened, extended or replaced (Honeywell, ZENNER). According to Honeywell, a meter with a damaged sensor cable is replaced with a new one.

Location of the Calculator Unit

On heating meters, the calculator unit usually sits on top of the flow sensor. It is detached from the pipe and mounted on the wall in the following cases:

• Cooling and heating+cooling: To prevent condensation, ZENNER and Danfoss require separate mounting. Danfoss says the unit should be placed higher than the flow sensor and the cables should have a loop from which water can drip.
• High temperature: ZENNER requires wall mounting at 90 °C and above. Calmet limits the medium temperature to 15–90 °C when the unit is on top of the flow sensor.
• Position where it cannot be read: The calculator unit of the Honeywell EW700 can be mounted separately up to 1 m away.

The distance is limited by the flow sensor cable: 0.5 m on the Danfoss SonoSafe 10, 1.2 m on the Minol Zenner C5 IUF.

Commissioning Checks

• Open the valves slowly: Opening suddenly causes water hammer. CEM requires opening the valve on the inlet side first, then the outlet side; Honeywell gives the order meter inlet, meter outlet and finally the supply line valve.
• Vent the air: Danfoss requires venting until the flow value on the display is stable.
• Check for leaks: There must be no leaks at the couplings and sensor connections.
• Wake the meter: The Minol Zenner C5 IUF is supplied in sleep mode (SLEEP 1); it is started by pressing the button for more than 5 seconds. The Calmet PM02 switches to normal mode automatically after about 10 liters of water have passed.
• Check the display: The volume should increase and the temperatures should be close to the real values. According to ZENNER, the temperature difference has a plus sign in heating and a minus sign in cooling. There should be no error code or warning symbol that stays on. For codes, see our guide Heat Meter Error Codes; for display values, see How to Read a Heat Meter.
• Installation point setting: On Minol Zenner C5 IUF versions with a programmable installation point, the selection can be made only once; if the button is not pressed, the meter sets itself to the return line after about 4 minutes. On Danfoss, this setting is changed with SonoApp and a Bluetooth hardware key.
• Record: Fit the seals; photograph the serial number, installation date and initial reading.

M-Bus and wM-Bus: Adding the Meter to the Reading System

• Wired M-Bus: The meter is connected to a two-wire bus; on ZENNER and Calmet, the wire polarity does not matter. Honeywell recommends 2×1.5 mm² cable for the bus.
• Address: The reading system finds the meter by its M-Bus primary address or by its secondary address based on the serial number. On the Minol Zenner C5 IUF, the primary address is set from the Adr menu on the display; on Danfoss, the default primary address and the secondary address are derived from the serial number.
• Wireless (wM-Bus): On the Minol Zenner C5 IUF, the radio interface is off on delivery and starts working when the meter leaves sleep mode. Telegrams are encrypted with 128-bit AES (ZENNER, Danfoss); the reading system cannot decode the data without the key. Ask the meter supplier for the keys together with the serial numbers.
• Assignment: Each serial number is recorded and assigned to the dwelling unit (block, apartment) in which it is installed.

Contact us about installation and adding meters to the reading system; our reading service is described on our Remote Meter Reading and Billing page.

Heat Meter Replacement: Recording Readings and Serial Numbers

When a meter that is faulty, has a depleted battery, is due for re-verification or has failed re-verification is replaced, the measurement chain must not be broken. In heat cost allocation, consumption is the difference between two readings; the last reading of the old meter and the initial reading of the new meter are the two ends of this calculation.

1. Old meter: Before removing it, photograph the reading on the main display together with its unit, the serial number and any error code; note the date.
2. New meter: After commissioning, photograph its serial number and initial reading, even if it is zero.
3. Calculation: For a meter replaced in the middle of a period, the consumption for the period is the sum of the old meter's difference (last reading − reading at the start of the period) and the new meter's difference (reading taken − initial reading).
4. Unit: The units of the old and new meter may differ (e.g. MWh and kWh); convert to the same unit before calculating.
5. Notification: Send the information to the building management and the meter reading company; the new serial number is added to the reading system and the old record is closed.

An ultrasonic model can be installed in place of a mechanical meter of the same size and length; the DN20 mechanical and ultrasonic models on our site have a body length of 130 mm. Models: Heat Meters, ultrasonic heat meter, and for DN50 and above large-diameter heat meter. For the question of whether to replace the battery or the meter, see our Heat Meter Battery guide. Because the removed meter contains a lithium battery, it must not be disposed of with household waste (ZENNER, Danfoss).

Common Installation Mistakes

• Reverse flow direction: Honeywell shows a reverse flow error, the Minol Zenner C5 IUF code 30, Danfoss the E12 negative flow alarm.
• Swapped sensors: If the temperature difference shows a minus sign in heating, check the positions of the red and blue sensors.
• Installation without a filter and unflushed pipes: Manufacturers explicitly require avoiding water containing burrs and dirt.
• Wrong body length: Installing a meter of the wrong length by forcing the couplings leaves it under stress.
• Shortening the sensor cable: Honeywell and ZENNER do not allow this.
• Installation at a point where air collects: Air accumulates in a meter at the highest point; the Minol Zenner C5 IUF shows code 40, Honeywell an air error.