American Standard ULN80-125 Operation, Installation And Service Manual page 19

INSTALLATION (Using Top Connect Only)
Typical installation showing two (2) Commercial Heaters in parallel manifold using top connect only.
Typical installation showing three (3) Commercial Heaters in parallel manifold using top connect only.
Typical installation showing four (4) Commercial Heaters in parallel manifold using top connect only.
HYDROGEN GAS
WARNING
Hydrogen gas can be produced in a hot water system that has not been used for a long period of time (generally two weeks or more).
HYDROGEN GAS IS EXTREMELY FLAMMABLE. To prevent the possibility of injury under these conditions, we recommend the hot
water faucet be opened for several minutes at the kitchen sink before you use any electrical appliance which is connected to the hot water system.
Do not light a cigarette, cigar or pipe. Do not smoke. If hydrogen is present, there will probably be an unusual sound such as air escaping through
the faucet as the water begins to flow. Remember, no smoking or open flame, near the faucet at the time it is opened.
Figure 10
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