Boiler vs. Hot water heater
I have a 4 family brownstone that has an oil boiler with steam heat radiators. I also have a hot water heater that I use in the summertime to heat the water instead of running the boiler. I’ve been giving some conflicting advice from my general contractor and my plumber. One says that in the…
I have a 4 family brownstone that has an oil boiler with steam heat radiators. I also have a hot water heater that I use in the summertime to heat the water instead of running the boiler. I’ve been giving some conflicting advice from my general contractor and my plumber. One says that in the winter I should cut the water heater off and let the boiler make hot water as needed. The other says that I should keep the water heater on low and use the hot water heater as a storage tank for the hot water. Does anyone have an idea which is more efficient and saves in oil bills.
To make hot water for domestic use using boiler water used for space heating, you need some type of heat exchanger to separate the potable from non-potable water, otherwise everybody gets sick.
So, yes, you can use a standard “water heater” to hold water in storage, but to heat it via the heating boiler, you’d need to pump water through an internal submerged tankless boiler coil or something external that you add on.
Indirect water heaters have the heat exchanger built in allowing you to plug right into your steam or hot water boiler safely and efficiently with no chimney connection and wrapped with 3″of insulation.
For comparison’s sake, the hot water in a standard water heater will cool down about 10Ëš per hour when not in use. An indirect water heater will lose something like 5Ëš per day under the same conditions.
This is a good thread.
Thanks MP, informative as always. Sounds like OP has the piping in series you describe.
To my question – can you do indirect hw using an existing hw heater as the tank… the answer as I understand it is that you could, but you’d lose efficiency with heat loss via the flue vs. a tank specifically made for indirect.
What a lot of plumbers were doing, and maybe some still do (I don’t know), when efficiency became a good thing to think about, was to run the cold water piping in series through the tankless boiler coil and then into the water heater, disconnecting the aquastat (the boiler temp-sensing on/off switch) so the boiler wouldn’t maintain a high internal temperature all of the time like it needed to when it was the sole source of water heating. So, when the boiler was running, the water was preheated by the boiler.
This made the tank-type water heater run much less.
It also cooled off the boiler, though. So then we all learned that we can’t pull BTUs out of thin air. The energy it takes to heat the water was bought and paid for regardless of where it came from.
That’s why I told the OP it makes no significant difference.
It’s possible the tank water heater is not piped to fire with gas, but that would be a waste because it would lose heat through the flue opening. There are insulated tanks specifically made for that with no openings except for the small pipe tappings.
Does that answer your question, ClydeFrazier?
MP,
Is it possible that the setup currycrab’s plumber or GC is describing is using the hot water heater as the storage tank for indirect water heating?
Is that practical – to add the piping and controls for indirect, but use the traditional hw heater for storage, rather than buying a new tank?
Word!,,,
Thanks for that link, Master Plvmber, looks like it has a lot of useful information.
They probably both run at about the same combustion efficiency so, in the winter, there’s no big difference to either arrangement you choose.
Sounds like you’ve got a tankless coil water heater in your boiler.
That’s the least good way to make hot water for most of the year. There is some slight advantage to it during the heating days.
If you’ve got a plumber and GC on site, why aren’t they offering you what may be the most efficient way to make hot water; an indirect water heater?
See what the U.S. Dept of Energy has to say about the subject: http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=13020