Is there a formula for the best size and number of electric water heaters for an apartment building?

Question

I would like a simple formula that factors in number of units, washmachines and tenents.

Answer 1

Yes, the go to Rheems website they have the software to make the water heater selection. It is fairly simple and accurate way to size the water heaters. If you are going to feed water to multiple tenents its going to be big, you might want to consider gas.

I would install electrical units to feed each unit rather than trying to feed hot water to multiple units. Somebodies going to get mad if Joe gets up at 4:00 and uses all the hot water so when bill gets up at 5:00 he has none.

Answer 2

If you don't get a better answer take these two things into consideration.

1) ask your electric company AND your water company for the size per occupant.
2) If possible triple that size and use one heater for three apartments based on expected occupancy.
3) have one extra on hand for a spare, connect heaters with hoses so you can swap the spare easily.
4) IF you do three then you can probably get away with one heater for four apartments because not everyone is going to be showering at the same time and if you run into a problem you can add the spare into the mix.

If its a REALLY big building you might be better off with a larger commercial setup or with on demand gas heat.

Answer 3

Gas is cheaper than electric in many parts of the country.

I believe the residential codes specify number of water heaters per X apartments. You may have 1 40 gallon water heater for each apartment plus a spare in case one of them dies. You could get away with 1 80 gallon and 1 40 gallon unit (with a spare 40 gallon unit). In terms of a mathematical formula, I doubt you will find one anywhere - just go with something which complies with the code and makes you a smart landlord.