How hot should my water be?

Kirk Heller

I just bought a home with a Vaillant oil fired boiler. The home is 75 years old and has radiators and a circulator pump. The boiler is set to produce water at 140 degrees. My home inspector told me he recommended settting it to about 180 degrees for greater efficiency. I found you guys and decided to ask the experts. HELP!

Thank you

Dave Yates (PAH)

That depends

on your home's heat loss and the amount of heat emitter present. It's entirely possible that 140 F will suffice. The only way to know for certain, other than taking a wait & see attitude, is to perform an accurate heat loss.

BTW, heating the water to 180 F instead of 140 F is less, not more, efficient.

Now, having said that, I'd be a bit concerned about seeing sustained flue gas condensation in either the boiler, the chimney or both with an outgoing water temp of 140 F and a potential return water temp of 120 F.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

todd s

boiler temp

The 140° setting is probably the low limit on the triple aquastat. If this is the case do not turn this up! This may be the domestic hot water temperature and you don't want it anywhere near 180°. You should contact your service company and get a relationship established before winter sets in so you'll have someone to call if you have an emergency. Very often the house seller doesn't have their unit looked at before the sale of the house, they figure its the next guys problem to deal with.

Plumbob

Assuming 140F really is the central heating water temperature and not something else, your inspector doesn't know what he's talking about. Not only is 180F less efficient, but it also results in less comfort...you will be heating the house with very short blasts of very hot water, so the temperature won't be very steady. 140F is distinctly better for avoiding the blast-furnace effect; lower temperatures are even better but your old-fashioned boiler would corrode at lower temperatures so the dial won't let you go lower.

Now on a very cold day, 140F may or may not be enough to keep the house warm. You'll have to monitor that and turn it up if needed. I guess 180F is more efficient in that sense...you never have to worry about whether the house will be warm. But I bet the previous owners had determined experimentally that 140F is plenty.

jim lockard

Kirk

Do you have a seperate water heater (round white tank ) if so then maybe you can play with the boiler temperature a little. If not and your domestic water is heated by the boiler, then leave the little knobs and dials alone. Find a good local servicer @ find a pro on the upper left corner or by the old fashion way of asking your friends and neighbors. Best Wishes J.Lockard

Steve Rockwell_3

Same Issue, But Condensing Boilers

So on condensing boilers, does that mean the water temp should be just barely hot enough to keep the house warm?

I've been playing with the parameters on my new Ultra, and have found that even in 32* weather here in Grand Rapids, the house seems to be fine running at a system temp of 134* through mostly baseboard (and a bit of standing iron). Obviously the system is running much longer than it would at higher temps.

Based upon what I've read, I would have thought the baseboard just wouldn't do the job at these temps, but it is. By the way, the baseboards don't even feel all that warm to the touch. By the way, the ci rads, which are on trv's, are just barely warm - just as they should be.

My question is this - on a condensing system, is it possible to run the system temp TOO low, even if the house is kept at the desired temp? Is there a law of diminishing returns, such that the system has to run so long at lower temps that it would actually be more efficient when run a few degrees higher?