What are the downsides for galvanized steel pipes + press fittings vs. welded steel pipes in a heating application? Diameter would be DN25/1".
Background: The customer specifies only steel, only welded connections for heating pipes starting at this size. The contractor wants to use press fittings, presumably because this way the installation will be easier. The rooms the installation will take place are rather full.
Are there good technical reasons to avoid galvanized steel pipes + press fittings? Corrosion, longevity, others?
Technical reasons: Regulations: Health and Safety Executive - Design Codes - Pipework
Corrosion, longevity: Corrosion, yes and longevity, no. If it's for galvanized hot water radiators you should be OK, but it's up to the customer and regulations. For drinking and bathing water you wouldn't want galvanized.
See these answers, people dislike galvanized - presumably so does the customer.
Answers from our sites:
Galvanized pipe life expectancy - particularly this answer and associated photo.
Are galvanised steel pipes suitable for supplying hot water?
If the customer has spoken with an Engineer or spent a lot on drawings and inspections they may be unreceptive to changes. If it's an idea they came up with on their own they might appreciate unbiased advice - the contractor would need to be certified to weld pipe, press-fitting is easier.