Hot Water Boiler - turning off during nite warmer weather, condensation risk

[zeppy]

how much of a problem is it if a large hot water boiler (2.5m btu) is turned off at night and back on in morning; this allows shutting down a pump which is expensive to run. there is a mixing valve in use connected to an older controller.

the only risk i see is condensation of flue gas, but if the boiler is turned up to 150 degrees, the chimney should dry out fine after 4-5 hrs of use

so condensation risk seems minimal.

interested in comments on this cost saving initiative

[toptech]

Condensation concerns are usally associated with reunning the boiler with return water temperatures below the manufacturers recommended lowest water temperature.
I think the greatest risk is freezing of pipes,radiators etc. I dont know your application, but sometimes the money saved turning the pumps off with severe cold weather isn't work the risk.

[zeppy]

clients are interested in turning off the boilers for a day or so when it gets warmer and then on when needed

if you run the hot water at above the boiler manuf recommendations is there a problem

it has been found to save a ton of money on pump costs and NG costs even after reheating of water costs are factored in.

seems prudent, but what are condensation risks, if any

[ascj]

clients are interested in turning off the boilers for a day or so when it gets warmer and then on when needed

if you run the hot water at above the boiler manuf recommendations is there a problem

it has been found to save a ton of money on pump costs and NG costs even after reheating of water costs are factored in.

seems prudent, but what are condensation risks, if any

What is the boiler application? Comfort heating, radiators or water coils? Process water heating? Reheat coils?

If it's just comfort heating, then why not just put an outdoor reset on it. That would eliminate the manual shutting down of the boiler and save ever more money.'

As far as condensation problems, as long as the boiler and venting is functioning properly and you keep the return temp above manufacture spec, you shouldn't have any issues.

[zeppy]

its baseboard heating and there is a mixing valve located 20 feet from boiler so NG being consumed is minimal as it gets warmer (valve is pretty much closed)

the primary reason for turning off boiler is to save on hot water pump electricity costs

problem is the mixing valve because if you turn on the boiler when the facility loop water is alot lower, the mixing valve will open up (not gradual) and flood the boiler with much cooler water and thats not good (eg water temp in shut down boiler may have cooled to 125 and rest of water beyond mixing valve might be 75-80) - thermal shock differential may not be healthy for cast iron boiler

how do cos. manage their hot water boilers (ie used for heating) when it gets warmer for several days and than colder requiring use of boiler??

[ascj]

how do cos. manage their hot water boilers (ie used for heating) when it gets warmer for several days and than colder requiring use of boiler??

As I said we manage it with outdoor reset. It will control supply temp depending on outdoor temperature and shut down system when outdoor temp is above set point.

[jayhawker]

What type of boiler is it fire tube, water tube. cast iron sectional or a low mass ?

[zeppy]

What type of boiler is it fire tube, water tube. cast iron sectional or a low mass ?


cast iron sectional - 14 sections, its a HB Smith 28a-14 boiler.

thanks

[flange]

we turn our off all of the time. condensation occurs in the flue piping when the warm gases come in contact with cool flue piping, and in areas where the flue is in a cool chase for example. we use a tee off the back of the boiler on eery install, and the condensation goes to drain for the most part. i dont worry about a little condensation getting into the boiler in most cases. i am a believer in energy savings, and to be fair if you are really worried about it, i would look at a reset schedule on your primary loop, even though you have a mixing valve, and most likely a reset schedule on your secondary(probably pneumatic). reset your primary to keep above condensing, but for most cases 180 degree water is probably not required right?