Request help choosing DHW replacement.

info43

30 years ago, we replaced our gas-steam boiler in a 6 family building. That boiler handled the heat and DHW for the building but we often got complaints about the hot water. We replaced that boiler with a WM EG-75 (steam heat only) and two 75 gal AO smith WHs. One WH worked most of the time but after we added the second we never got complains about hot water again.

It’s now time to replace the WM EG-75. EDR is 495 so we will get a smaller boiler. I am not sure which route to go on the DHW. I can keep two 75 gal AO smith WHs (cost about $175 per month in gas to operate), my plumber recommends on demand tankless but there is an indirect option with a tank. Any suggestions would be appreciated.

Larry Weingarten

Hello, I'd begin by seeing if there is anything that can be done to reduce the hot water demand. Even the simple step of going to 2 or 1.5 gpm showerheads might save you getting a second heater. After conservation measures, then consider an indirect powered by an efficient boiler. Just my 2 cents

Yours, Larry

lchmb

How is your water? Mineral issues, PH? On demands are nice, but they must be serviced more and dont like build up in the small turns inside them...I have done storage tanks with an on demand. Maybe contact Rinnai or a brand used in your area to size the load and see what they recommend..

info43

@Larry Weingarten a few years back the city gave rebates to change the toilets and shower heads, so we changes all of ours. I don't remember what the gpm is on the heads. I did turn off one of the WH after that, we a got a couple of calls so I turned it back on. There are about 30 adults in the building so I think in the morning or evening there are a lot of back to back showers. I will get another Weil Mclain and it looks like they have a tankless option that's got me thinking about changing from the WHs. If I go that route, I would need a tank as suggested.

@lchmb It is NYC tap water so I think its fine. I don't live in the building so I like the water heaters, I change the rods 5 years in and the WH about every 10, drain a little from the bottom every few months and thats it. I like the idea of indirect but my plumber strongly recommends the tankless. I suggested the tank with ondemand but he didn't like it either.

lchmb

If your changing ever 10 years I'd stick with what works... but that's me.... My concern would be the load and flow rates..

SeymourCates

@info43

Ask your "plumber" the following question:

"What happens to the tankless water heater when four people (out of the six) get into the shower at the same time in the morning and require a total of 10 GPM?"

Then tell him the following:

"You know, a flow rate of 10 GPM is going to require 300,000 BTUH and it will likely require a 1.25" gas line"

The look on his face will be priceless.

info43

@SeymourCates my plumber suggested I put in two 10gpm tanklesses. Now add the steam boilers I'd be up to 750k btu? I guess that would be an ever bigger gas line.

SeymourCates

The cost of achieving that is massive.

Do yourself a favor and put in one of the AO Smith 75 gallon units. Store the water as hot as possible and mix down to 120F. Put in low flow shower heads (not more than 2 GPM) and you'll be fine.

Replace the anode every two years without fail.

info43

one last question, If I went with the tankless that was built into the boiler and had it feed a 100 gallon indirect tank, what happens in the Summer? Will the boiler create steam or will it only heat up to 160-180 degrees?

info43

@SeymourCates hmm, that is interesting. Right now the WHs are set to one of the lower temperatures settings as there is no mixing valve. I will look into adding one to it. Thanks