Do you want to divide your installation into 2 systems - open vented and closed one?? Are you considering a gas boiler but don't want to get rid of a coal or solid fuel boiler? Below we'll describe how to size correctly a plate heat exchanger for a boiler. As an example we'll use a gas condensing boiler, but the general rule of sizing will be very similar in case of other fuel.
How to select a heat exchanger for a condensing gas boiler? The answer to a common question we receive from our customers.
Answer from NORDICTEC-STORE.COM
For NORDIC TEC plate heat exchangers, there is a converter designed for sellers in brick-and-mortar stores, where selection of a heat exchanger should be quick and efficient, and sellers may not necessarily want to use computer selection programs. Especially since customers may not always have knowledge about all the parameters of their installation.
✅ To connect a condensing gas boiler to the system using a plate heat exchanger, we apply a simple principle. For every 10kW of the condensing boiler, the heat exchanger should have a heat exchange surface of about 0.30m2. Therefore, we do not select the exchanger by comparing its nominal power with the boiler power (which is the most common cause of incorrect selections), but by finding the heating exchange surface on the exchanger.
Following the 10kW -> 0.3m² rule, a 24kW boiler should be served by a heat exchanger with a surface of about 0.7m².
This selection accounts for a sufficiently large oversizing so that the exchanger can serve for years, even when its surface begins to scale with lime (after a few heating seasons, this process always occurs to a greater or lesser extent in water-filled installations, especially in open systems).
✅ If the installation is new or modernized, in new construction - we can slightly reduce from the universal 0.30m², down to a maximum of 0.25m² per 10 kW. Going lower is not recommended, due to the expected aging process of the exchanger in the installation over time. If we want the device to be durable, it is best to stick to 0.25-0.30m².
This converter works well for sizing heat exchangers for condensing boilers with a working temperature of 45-50°C. However, it can also be successfully applied to coal, eco-pea, or pellet boilers, which operate at slightly higher temperatures (usually 50-60°C).
❌ However - the converter will absolutely not work for heat pumps, where for every 10kW of heating device, you need a heat exchange surface on the heat exchanger even three times larger than in the case of heating boilers. This results from the specificity of operating at very low temperature differentials - especially when the heat pump serves a system operating at very low temperatures (e.g., fully based on underfloor heating).
The converter may vary for other manufacturers if they use plates of different thickness (which affects the quality of heat exchange) and depending on how heavily corrugated the plate is. In the case of NORDIC TEC exchangers, the plate is corrugated, which induces turbulent flow - significantly improving heat exchange. The plate has a thickness of 0.3mm or 0.4mm (depending on the model). Apart from these nuances, it can be assumed that the converter of other manufacturers will be approximate or similar.
✅ The above selection method is suitable for the simplest installations, where the heat exchanger is intended to serve the boiler entirely (not for connecting additional heating circuits only, etc.). In the case of more complex installations, the selection should always be made by a qualified person. The responsibility for the selection lies with the contractor or the person making the selection.
If you are looking for help in selecting an exchanger - feel free to contact our selection department.
A brief visualization of the recommended heat exchange surface area (i.e., the surface area of the heat exchanger plates) in relation to the output power of a gas boiler (implicitly also for other fuels, if they operate at standard temperatures). The surface area is listed in square meters in the left column and on each bar.
Some manufacturers and sellers always provide this information in the product descriptions. ✅ Nordic Tec always makes this information available – it may be listed as plate surface area or heat exchange surface area, and less frequently as heat transfer surface area.
Below is an example comparison of the heating exchange surfaces of devices from the Nordic Tec Ba-32 series, with a 1-inch thread. With an increasing number of plates, the heating exchange surface increases, allowing for the handling of a larger boiler. The heating exchange surface is presented in m².
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Update: 11-2024
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Comments
Plate to plate heat exchanger information.
By: Kevin O' Brien On 2026-03-17Hi I’m looking speak with someone on all things plate to plate heat exchangers for a gas boiler on a domestic heating system please. I.e sizing, piping of and so on.
Look forward to hearing from you.
Many thanks.
Replied by: Adam Bert On 2026-03-18