testo 435-4 - Multifunction meter w/ memory, software, and differential pressure

Order-Nr.  0563 4354

  • Integrated differential pressure measurements for flow velocity

  • Optional wireless (RF) temperature and humidity probes for remote measurement

  • Backlit LCD for easy viewing

  • Built-in memory stores up to 10,000 measurements

The testo 435-4 multifunction meter is perfect for monitoring, analyzing, and diagnosing indoor air quality, wherever you need to take important IAQ measurements. In addition, you can easily pinpoint and troubleshoot problems with HVAC systems, and immediately see the results of corrections. Commissioning, validating, benchmarking, or simpy adjusting HVAC systems are all easy with the testo 435-4.

Product Description

The testo 435-4 multifunction meter allows you to carry out all the measurements that are necessary to check and adjust ventilation and air conditioning systems, and to assess the quality of indoor air.  The 435-4 accepts a wide variety of probes to measure and record airflow, humidity, temperature, and indoor air quality (IAQ) readings.  With the included ComSoft Software, this data can be organized by location, analyzed, and reported.
Probe dependent menus and selectable user profiles ensure that the testo 435-4 multifunction meter is always ready to use.  Easy setup of user defined IAQ and airflow / duct profiles allows for fast measurement of many different tasks, and with a wide variety of probe choices available, the testo 435-4 is ready to handle a vast array of HVAC / IAQ applications.  The superb data handling will keep your readings organized and ready, however you need them, whether in a quick printout on-site, or for further analysis for placement into a report.
testo 435-4 highlights:
  • Integrated differential pressure measurement for flow, and monitoring HVAC
  • Data recording up to 10,000 readings
  • ComSoft PC Software for analyzing, archiving, and documenting data
  • Wireless or cable humidity probes
  • Optional light (Lux) probe
  • Optional comfort level probe


Delivery Scope

testo 435-4, PC software, USB cable, batteries, and conformity certificate
Temperature - NTC

Measuring range

-58° to 302 °F / -50 to +150 °C


±0.4 °F (-13° to 166.8 °F) / ±0.2 °C (-25 to +74.9 °C)

±0.7 °F (-58° to -13.2 °F) / ±0.4 °C (-50 to -25.1 °C)

±0.7 °F (167° to 211.8 °F) / ±0.4 °C (+75 to +99.9 °C)

±0.5 % of mv (Remaining Range)


0.1 °F / 0.1 °C

Temperature - Type K TC

Measuring range

-328° to 2498 °F / -200 to +1370 °C


±0.5 °F (-76° to 140 °F) / ±0.3 °C (-60 to +60 °C)

±(0.4 °F + 0.5 % of mv) (Remaining Range) / ±(0.2 °C + 0.5 % of mv) (Remaining Range)


0.1 °F / 0.1 °C

Temperature - TC Type T (Cu-CuNi)

Measuring range

-328° to 752 °F / -200 to +400 °C


±0.5 °F (-76° to 140 °F) / ±0.3 °C (-60 to +60 °C)

±(0.4 °F + 0.5 % of mv) (Remaining Range) / ±(0.2 °C + 0.5 % of mv) (Remaining Range)


0.1 °F / 0.1 °C

Humidity - Capacitive

Measuring range

0 to +100 %rH


See probe data


0.1 %rH

Absolute Pressure

Measuring range

0 to 800 InH₂O / 0 to 2000 hPa


See probe data


0.1 InH₂O / 0.1 hPa

Velocity - Vane anemometer

Measuring range

0 to 11811 fpm / 0 to 60 m/s


See probe data


1.97 fpm (Ø 60 mm vane + Ø 100 mm vane) / 0.01 m/s (Ø 60 mm vane + Ø 100 mm vane)

19.7 fpm (Ø 16 mm vane) / 0.1 m/s (Ø 16 mm vane)

Velocity - Hot wire anemometer

Measuring range

0 to 3937 fpm / 0 to 20 m/s


See probe data


1.97 fpm / 0.01 m/s

Ambient CO₂

Measuring range

0 to +10000 ppm


See probe data


1 ppm

Differential pressure (internal sensor) - Piezoresistive

Measuring range

0 to +10 InH₂O / 0 to +25 hPa


±0.01 InH₂O (0 to +1 InH₂O) / ±0.02 hPa (0 to +2 hPa)

±1 % of mv (Remaining Range)


0.01 InH₂O / 0.01 hPa


80 InH₂O / 200 hPa


Measuring range

0 to 100000 Lux


See probe data


1 Lux

0.1 Hz

General technical data


9 x 3 x 2 in. / 220 x 74 x 46 mm

Operating temperature

-4 to +122 °F / -20 to +50 °C


ABS / TPE / Metal

Protection class




Battery type

3 x AA 1.5 V

Battery life

200 h (typical vane measurement)

Display ligthing



10,000 measuring values

Storage temperature

-22° to 158 °F / -30 to +70 °C


15 oz. / 428 g

Air Probes

CO probes

Ambient CO probe

Order Number: 0632 1235

Humidity probes

Humidity/temperature probe

Order Number: 0636 9735

Immersion / Penetration Probe


Absolute pressure probe 29 psi

Order Number: 0638 1835

RFID Probe

Humidity probe head

Order Number: 0636 9736


Additional Accessories

Flow measurement in the ventilation duct using a thermal anemometer and vane anemometer

Testo offers compact anemometer probes and pitot tubes for measuring the flow and volumetric flow in the ventilation duct.

Selecting a suitable probe or measuring instrument depends on the flow velocity in the ventilation duct. This can be broken down into three sub-ranges:

  • Low flow velocities: 0 to 5 m/s => thermal anemometers and thermal probes are suitable for this (order no. 0635 1535, 0635 1025)
  • Medium flow velocities: 5 to 40 m/s => best results are achieved by the 16 mm vane anemometer und Flügelrad-Sonden (order no. 0635 9535)
  • High flow velocities: 40 70 100 m/s => the pitot tube provides the best prerequisites (see following application)

The flow sensors for duct measurement are all equipped with telescopes making them easy to use in large air ducts. Air temperature and humidity can also be measured with the same probe as the flow velocity if required. According to the required application, choose between a thermal probe, vane probe or pitot tube for measuring the flow measurement in the duct.

Measurement at the air outlet

Every duct inlet and outlet should only contain the volumetric flow that according to calculations is a basic prerequisite to an efficient functional system.

Large vane anemometers with 100 mm diameters are suitable for measuring the volumetric flows at duct outlets (order no. 0635 9435), as it integrates the flow velocity over a larger area thereby determining disturbance from the air grille (loop method).

To measure the suction or blowing vents of air grilles and poppet valves our volumetric flow rate funnel set is ideal (order no. 0563 4170) as is the large 100 mm vane anemometer (order no. 0635 9435) The entire volumetric flow is recorded with the aid of the funnel without the need for conversion on the basis of the flow velocity and area. This method of flow measurement is simple and reliable.

Measurement of the air and surface temperature

For human beings to be comfortable and perform at their best, it is crucial that the rooms they occupy are correctly air conditioned. As well as the structural conditions and personal perception, the following factors also contribute significantly to the existence of a pleasant indoor climate: the indoor air and surface temperature of walls, windows, floors and ceilings.

There is a range of optional temperature probes available for the testo 435. Our temperature probes with a sprung cross-band sensor element for measurement on surfaces are outstanding. The sprung cross-band sensor element fits on any surface, taking the actual temperature of the measured object in just a few seconds (for example the fast-reaction surface probe, order no. 0602 0393).

In order to allow a fast measurement of air temperature, the temperature sensor is free in our air probes (e.g. precise, robust NTC probe 0613 1712). Immersion/penetration probes can also be used for measurements in air. However, the response time is then about 40 to 60 times higher than the indicated value which was measured in water.

Differential pressure measurement on filters

Air conditioning systems are equipped with filters which prevent dirt from the outside air entering the indoor air. These filters are to be inspected regularly to make sure they are still fully functional. To do this, the pressure is measured in front of and behind the filter. The result is the differential pressure. If it is too high, the filter is contaminated and needs changing.

testo 435-4 uses the integral sensor to measure the differential pressure within the 0 to 25 hPa range. The differential pressure measurement is temperature-compensated for exact readings. Magnets on the rear of the instrument allow hands-free work.

Measurement in the ventilation duct using a pitot tube

Observance of air flows in the ventilation duct is of utmost importance for the function of the ventilation and air conditioning system.

The internal differential pressure sensor of the testo 435-3 is used for measuring in the case of high flow velocities and very contaminated flows, and the pitot tube for an air velocity ranging from 0 to 64 m/s. The testo 435-3 simultaneously displays pressure, flow and volumetric flow.
Magnets on the rear of the instrument allow hands-free work.

Lighting measurement

Suitable lighting in the workplace provides workers with sufficient light to be able to perform their jobs well. It helps to prevent mistakes being made, premature tiredness setting in, and maintains alertness.

testo 435-2 and the Lux probe (order no. 0635 0545) can be used to measure and assess luminous intensity (natural or artificial light).

Turbulence measurement

The air velocity in rooms directly affects thermal comfort. The turbulence and draught levels can be referred to in the assessment of comfort.

The level of turbulence indicates the air velocity fluctuation and intensity of air flow in a room.

The draught rate can be generally understood as the unwanted cooling of the body due to air movement. This is defined by the percentage of people who feel uncomfortable.

The non-directional comfort probe (order no. 0628 0109) has been specially designed to measure the turbulence level in accordance with EN 13779, and to assess the draught rate. In conjunction with our multi-functional measuring instrument testo 435, standard-compliant measurement results can be analyzed directly in the device.

U-value measurement

When redeveloping or renovating old buildings, it is crucial to be able to determine quickly if heat is being lost through the windows and walls. Only then can energy costs be reduced and redevelopment measures carried out efficiently.

When assessing thermal transmission, e.g. in old buildings in need of renovation, the U-value is one of the most important values. It enables thermal assessment, e.g. leaks or the smallest air flows at windows.

3 temperature values are required for calculating the U-value:

  • Outside temperature
  • Surface temperature of the internal wall
  • Indoor air temperature

A radio probe is needed to determine the U-value (order number: 0614 1635); this is placed in position outside. It transmits the readings to the measuring instrument inside. To measure the surface temperature the three wires of the U-value probe are attached to the wall with plasticine. The air temperature is recorded by a sensor located on the probe plug. The measuring instrument testo 435-2 automatically calculates the U-value from the three values and shows this on the display. The advantage: there is no need for manual calculation; the result is quick and accurate.

In short, the testo 435-2 allows you to calculate the U-value quickly and accurately, as well as measure parameters for air conditioning, ventilation, and indoor air quality.

Measurement of indoor air quality (CO2)

Bad indoor air quality due to high concentrations of CO2 can cause tiredness, lack of concentration and even illness. Therefore, to ensure sufficient indoor air quality the CO2 concentration should generally not exceed 1 000 ppm. Values of 700 to 1 500 ppm can be viewed as the "reference range".

The IAQ probe (order no. 0632 1535) is particularly suitable for monitoring indoor air quality controls. This probe can be used to record CO2, temperature and relative humidity at the same time.

CO measurement

Carbon monoxide (CO) is an odourless, invisible and tasteless gas, but also poisonous. It is produced during the incomplete combustion of substances containing carbon, such as coal, wood, oil, natural gas, etc., in heat sources and combustion engines. The CO concentration will increase quickly, particularly if there is not enough oxygen available. This may have adverse effects on health.

The ambient CO probe (order no. 0632 1235) and testo 435-1 are able to detect even the smallest quantities of CO in ambient air.

Product Brochures