10 day vacation. Should I turn off oil boiler? ( tankless coil hot water)

yes

At your electric rates… yeah, an electric water heater is mildly insane.

Just turn off the boiler ("emergency" switch) Then just turn it on when you get home. No hassle.

You can also shut off the water as @HVACNUT suggests — provided that the main shutoff valve actually works…

Can't you isolate the house from the sprinkler system?

Anyone can do what they want. The oil company loves a tankless coil that’s for sure.

A brief word, if I may, about tankless coils and warm start boilers in the summer. And, for that matter, oil fired water heaters. Yes it does take some oil to keep a warm start boiler warm in the summer, and this does appear to be wasteful. But — how much is it, really? Has @ethicalpaul ever actually measured the run time of such an arrangement? I very much doubt it. Let's suppose, though, that the burner needs to run about 10 minutes every four hours, for a total of an hour a day, and let's also suppose that it is a more or less typical residential boiler at perhaps with a 1 gph nozzle. OK. At current prices around here, that's a whopping $5.00. Let's also suppose that the electric water heater needs to generate about the same number of BTU. Again, around here — at $.40 per kW, — that's around $16.00 worth of electricity.

Um… and just what is wrong with that tankless coil again, @ethicalpaul

And kindly don't get me started on heat pump water heaters. I have nothing against them — for new installations, or all-electric homes or jurisdictions where all-electric is mandates. Unless they have huge tanks, they WILL drop into resistive heat mode or give you a cold shower for any use more than two people in a flat, but they do save energy. They also cost a lot up front. And have a relatively short life (10 years?).

And kindly don't get me started on heat pump water heaters.

That's a strange way to have a discussion! But OK, I won't!

I can understand @ethicalpaul ’s position. A lot of people had that same experience in the years around the turn of the century, when electricity was relatively inexpensive and oil prices were going through one of their periodic spikes. In many cases, a tankless coil on an inefficient oil-fired boiler was an expensive way to make domestic hot water. That was especially true when the coil was limed up with calcium deposits and could no longer deliver enough hot water for a decent shower. The plumber would come in, install a 40-gallon electric water heater, and voilà—more hot water and, quite often, a lower operating cost.

In those situations, the old oil boiler might have had an effective water-heating efficiency, or energy factor, of only about 0.40. With electricity at roughly 8 cents per kWh, the electric water heater could easily win the operating-cost comparison.

Inefficient Oil Boiler energy factor = 0.40 Electric is about 8 cnets for a kWh

The important point, however, is that the oil-fired boilers Paul formed that opinion around are, for the most part, no longer representative of what is commonly installed or operating today. A modern oil-fired boiler with a tankless coil—such as a Weil-McLain, Peerless, or Burnham—can typically operate in the range of 80% to 85% combustion efficiency when properly set up. If we then account for additional standby and off-cycle chimney losses, the effective water-heating efficiency may still end up somewhere around 0.70. At that level, depending on current oil and electric rates, the tankless coil can be competitive with—or even less expensive to operate than—an electric water heater.

Current Day Oil Prices and Electric Cost comparison

That is the part of the discussion I believe Paul either does not see, or chooses not to accept. His conclusion is based on a real experience, but it is not universally applicable. As long as he continues to evaluate the subject through the lens of a heat pump water heater in his own basement, he is unlikely to be persuaded that his solution is not the right one for everyone. Oil would need to cost almost $9.00 per gallon to make Paul's argument valid when looking at a $0.31 kWh price for electricity.

As long as Paul continues to promote the “tankless coil elimination” theory as a blanket rule, I believe some of his otherwise valuable information—particularly on steam—will continue to be undermined by that overly broad and, in many cases, erroneous position on domestic hot water production.

I believe this is the 12th time I have given Paul the facts, and each time I never get the "AH-HA" moment from Paul, the way I got when he did his "Dimension A" video on his Steam Boiler. But can we be sure that the video was not altered just to prove his point?

LoL…are you guys trying to coax @ethicalpaul to make another one of his very informative videos?

I owned a rental home with a tankless coil in an oil-burning hot water boiler. The mixing valve failed and sent 180 degree water into the fixtures. That was the straw that broke the camel's back—keeping that thing running all summer even though I wasn't paying for it just struck me as an oil company's dream and a homeowner's nightmare. Call me stubborn…I think people are stubborn about tons of things (such as refusing to believe that a heat pump water heater is cheap to run), it's human nature.

> As Paul misses the point with the reply about my spoof on the "Dimension A" video.

You brought it up and seemed to suggest that I faked the video. Of course I focused on that.

PS: I do like and respect you, just like so many other people in my life with whom I don't agree with about every topic

@CoachBoilermaker It's ok to switch your boiler off at the stairway or at the boiler. You can put other units in vacation mode if they have that option. Let others know where the switches are if they don't already, just in case.

@ethicalpaul Above, you mention a "mixing valve" failed and sent 180deg. water to the fixtures? Are you sure it was a mixing valve and not a tempering valve? Maybe a Watts 70A, for example? That valve would indeed fail to hot and could scald. A mixing valve would have a thermostatic mix and be called a thermostatic mixing valve. If a true mixing valve- one that is thermostatic fails, they are designed to fail so cold water runs through the valve and not scalding hot water. Do you remember which one you had back then?

Yes. You are correct. A thermostatic mixing valve is also required by code in many areas now. A tempering valve, I'm not too sure if they are code compliant for domestic hot water. I just completed a newly renovated apartment complex that required proper hot water thermostatic mixing valves.

If the installer, service technician, or plumber fully understood how a tankless coil operates under the many changing conditions that occur throughout the year, they would never install or service one without a properly functioning tempering or mixing valve.

The water leaving a tankless coil can range from more than 200°F to as low as approximately 110°F, depending on where the boiler happens to be in its operating cycle. That is why a proper mixing valve is essential. It adds cold water to the hot water leaving the boiler’s tankless coil before that water reaches anyone’s hands or other parts of the body.

Unfortunately, some installers do not fully appreciate the danger until a customer is injured and a lawsuit follows.

Yeah I probably called it the wrong name. But it was neither tempering nor mixing. It was attached at the boiler in yes a typical bypass way, but some part of it failed.