Two water heaters in parallel

[Jm66208]

A four plex i looked at has two 40 gal water heaters plumbed in parallel supplying hot water to all four units, plus two wash machines in the basement. One water heater needs replacing.
Tennants have always complained about lack of hot water.
Im looking at options to improve the situation.
1. Replace the two 40 gal with one 100gal.
2. Replace both 40's with two 50 gal. Plumbed in parallel.
3. Split the system into two halves and have one 50 gal supply each half of the building.

Any suggestions are greatly appreciated.

 

[CountryBumkin]

If they are in parallel, then is one water heater supplying hot water for two units, and the other heater supplying water for the other two units plus the washing machines?

However if Tenants are complaining now, then 40gal must not be enough. Does these units have bath tubs and dishwashers?

 

[Sponsor]

 

[Jm66208]

,
No, both water heaters simply are tied into a common hot water trunk line. A configuration that never really works. One water heater is probably doing all the all the work, and the other one simply sits there idle. Some say that if the length of pipe from the heater to the trunk line is equal on both heaters they will both feed equally. I think that's bs.
There's no way to really know

 

[CountryBumkin]

Sounds like switching to one 80 gallon or 100 gallon heater would be better setup.

 

[Jm66208]

Yes, but slower recovery during hi demand periods. Two 50s in series may be better, but ive never done it. Some say set the first heater at a lower temp to "pre heat" the water, then set the second to higher temp. This way, both heaters share the load. Others say to just set both to desired temp.

 

[Jm66208]

Another thing...if I divide the plumbing system into two halves. One heater will service two units, and the other heater will service two units, plus the two wash machines. Just how the place is set up...

 

[hj]

I ALWAYS connect them in series, that way you have double the btu input for all the hot water and do not have to worry about unequal piping AND water heaters to give equal flow. Unless they are electric where are you going to find a residential 80 gallon, much less a 100 gallon, water heater these days.

 

[Jm66208]

Thanks hj. Any thoughts on setting temps differently?

Why? You want the maximum hot water to the faucets.

 

[CountryBumkin]

Are these Gas water heaters? The gas heaters have pretty good recovery rates.
http://cdn.globalimageserver.com/fetchdocument-rh.aspx?name=advantageplus-advantageplus-spec-sheet

 

[Jadnashua]

For maximum output volume, set both tanks to the desired outlet temperature. You can then slowly reduce the first one in line if people never run out of hot water.