Boiler with heating coil running too much?

cluelessandlost

So, I have an oil-fueled steam boiler (Burnham MST288) with a heating coil for hot water. And I feel like it's running way too much in the summer, almost once every hour. I pretty much don't use hot water during the summer, at most taking lukewarm showers (though recently it's been cold showers due to the heat waves), and I can't help but think this is way too inefficient.

I have very limited space in my basement and don't quite have the money to afford a separate water heater at the moment, so I'm wondering if there's anything I can do to not be so wasteful of oil? Would it help to turn it off and then turn it on only when I need warm or hot water, so probably every 2 weeks or so? Or would that actually be worse because it let the water get too cold so it has to run longer to heat it back up again? I also read that boilers will run into issues if the water gets too cold, and there's bacteria concerns if the water temperature drops below a certain amount?

mattmia2

That is how tankless coils work, they keep the boiler hot all the time in case you need domestic hot water.

Won't hurt anything to turn it off, at least not anything that wasn't about to be a problem anyhow.

Still use the hot water even when you have the boiler turned off, if you let it sit for a couple weeks is when you could have a problem. A tankless coil is a minimal legionella risk because water is constantly flushed through it, it doesn't store a large quantity of water.(and about 100 other things that could be said about legionella)

EBEBRATT-Ed

The boiler is not going to stay hot for two weeks if you shut it off.

#1 you want the water coming out of the hot faucet at 120 degrees any hotter is a waste

#2 Post pictures of your tankless heater and the piping. It should have a mixing valve on it set to 120 degrees

#3 your boiler water temp. Everyone is different you need at least 140 degree HW in the boiler to get hot water. You may have to adjust it from 140-190. You want the boiler water temp as low as possible to save fuel and still get the HW you need. You adjust the boiler water temp at the low limit control

The reason for not setting the mixing valve all the way to hot is because in the winter the boiler water will be 212 deg and you need the mixing valve to lower the hot water temp so you dont get burned.

Tankless coils are not the best to heat HW with but in a two person household or so many people survive with them and are happy

HVACNUT

There should be an aquastat mounted in the coil. What temperature is it set to? If you remove the cover, there might be a White dial inside for the differential. 140° with a 10° differential is fine.

The MegaSteam is one of the most efficient steam boilers. Having a tankless coil certainly doesn't help efficiency, but making sure its clean, the burner is producing clean combustion with 0 smoke, and proper draft will help. When was the last time it was tuned?

cluelessandlost

Here's what my coil looks like. The Honeywell aquastat was set to 160-170 degrees, so I adjusted it down to 130.

Does that look okay? I got my boiler's annual service done a couple weeks ago.

EBEBRATT-Ed

130 is a bit low but I don't think you will get much hot H2o at that temp.

With the mixing valve you have has a thermometer on it. Turn on the hot and cold for the shower and let it run. Then set the low limit on the boiler to maintain 120 water temp

cluelessandlost

How do I set the low limit on the boiler? There's only this one aquastat with a temperature I can adjust that I can see. It's a Resideo L4006A2015, and when I looked it up, it says it can be set as a high or low, so I'm actually not too sure what I just did when I changed the temperature…

I ran a hot shower tonight and the water was fine, but I don't know how much of that is the water not having cooled yet.

EBEBRATT-Ed

The Honeywell aquastat. The same one you adjusted from 170 down to 130. That is the low limit. That aqustat keeps the boiler at the temperature you set it for 24 hours a day 7 days a week, it runs the boiler so you can get hot water weather your thermostat upstairs is calling for heat or not.

cluelessandlost

Oh, I misunderstood your post and got mixed up with the temperature gauge and the low limit. I just turned it up from 130 to 140 and the temperature gauge shows 110.

The hot water feels really comfortable. Do I need to turn it up more until it reaches 120? Is a lower temperature something that can harm the boiler?

HVACNUT

https://forum.heatinghelp.com/discussion/comment/1860726#Comment_1860726

If you take the cover off the aquastat, there's a white dial to set the differential. Don't go higher than 10.

cluelessandlost

Just opened up the aquastat and the white dial inside is set to 10. So that seems okay.

With the new setting at 140 my boiler is no longer going on every hour. Hoping these settings are safe!

EdTheHeaterMan

The temperature on the Caleffi Thermometer are only accurate if a hot water tap is turned on. If there is no hot water running thru the pipe, then the thermometer is measuring the water temperature that is in the pipe when you took the picture. If that water was not moving thru any pipes, then that water may have a chance to cool off.

The temperature setting on the RESIDEO L4006 is what the oil burner will come on to maintain. when the boiler water gets below 130° the L4006 will turn on the burner. the white dial set at 10° inside, will make the burner operate until the boiler water gets to be 140° (130° limit setting + 10° Diff = 140° cut off temperature). Since you are using cold water from your city water service or well water pump, you most likely have 52° to 62° water entering the tankless coil. That potable water will absorb heat from the boiler water as it moves thru the tankless coil.

Depending on how fast the water is flowing thru the coil, the water exiting the tankless may absorb 50° to 80° from the boiler water. Now lets think about that process for a minute. Lets say 58° water enters the tankless coil and travels thru the boiler water going around and around the 140° boiler water, absorbing lets say 62° of temperature from the 140° boiler water. That would make the potable water exiting the tankless coil 120°. (62 + 58 = 120).

If you don't need any hot water for some time (more than a day) then you can turn off the burner and the boiler temperature may drop to 60° over the next day (if the basement is 60°). Now when the 58° water enters the tankless coil, and the water passes thru the 60° boiler water, there is next to no heat for the potable water to absorb. You will get 60° water out of the tankless water heater. That should not present any problem with your burner, tankless coil or boiler.

There may be a chance for water to leak around the tankless coil gasket. that would most likely be boiler water passing thru the gasket because the cooler metal and gasket will shrink. if it shrinks enough, ther may be a leak. If there is a leak you have 3 wsud to fix the problem.

1. increase the boiler temperature bsack to 130° or higher to make the metal and gasket expand a hopefully seal up any leaks.
2. fix the leak. That may just involve just tightening up on the coil bolts, or replacing the gasket and snugging up on the bolts at least two more times after the boiler operates for 500 hours and again at 1000 hours.
3. leave the leak there if it is small enough, just turn off the boiler feed water to make sure no additional water is exiting the boiler.  Just be sure to turn the feed water back on before you fire up the boiler again. You don't want to fire the boiler with no water in it