Water tank manufacturers can compare tanks made of the same material by weighing them, or they can cut the tanks open for a full inspection, analysis, and comparison.
1. Inner tank material issues
As we know, there are many types of stainless steel — 316, 304, 301, 202, 201, 200, 430, 444, and so on. Different grades vary widely in corrosion resistance and other properties, so naturally their prices also differ significantly. The cost per ton can be several thousand to over ten thousand RMB apart. When a manufacturer uses a cheaper grade of stainless steel instead of 304#, an untrained eye usually can’t tell the difference. But after the product has been in use for a while, problems start to appear — the tank corrodes and leaks because of the poor material quality. This causes unnecessary losses for the user, and in turn, brings serious trouble for the seller.
2. Actual inner tank volume
Since the inner tank is hidden in the middle of the outer shell, users can’t see it directly. Some manufacturers take advantage of this fact and produce inner tanks that are much smaller than the advertised dimensions. That way, they save on materials. The actual volume should be no less than 90% of the labeled value.
3. Insulation material
The type of insulation material used has a big impact on how long the tank retains heat. Under normal room temperature conditions, the standard requirement is that the water temperature inside the tank should drop by no more than 5–7°C over 24 hours. Different manufacturers use different insulation materials — some use low-density foam, which makes it hard to guarantee good insulation performance. This, in turn, increases the energy consumption of the heat pump water heater.
4. Outer shell material
Some manufacturers make the outer shell and the top/bottom end caps from very thin material, and a few products even skip the bottom cap entirely. This not only makes the tank look cheap, but also makes it prone to rust, more likely to be damaged during shipping, and shorter in overall service life.
5. Coil material for coil‑type tanks
There are currently two types of coils: copper and stainless steel. Which is better? It’s hard to say. Copper coils can leak because the copper tube is often too thin, and they are also prone to galvanic corrosion at the weld point with the stainless steel inner tank. Stainless steel coils, on the other hand, are well liked by users because of their good sealing properties and strong corrosion resistance.