I'm a complete newbie when it comes to HVAC. I did manage to install a new thermostat with help from here so I try again. I have a oil burner baseboard hot water system. My hot tap water is also heated through the burner. I know how I can change the temperature for the tap hot water, but can I change the temperature of the water that goes through my baseboard radiators? I attach a picture of what the system looks like since I am not able to describe the it in any meaningful way hoping the picture may tell someone something.

I think I found the aquastat for the heating. It's on the boiler itself. I have attached two new pictures. Is there any benefit to setting the temperature up? I also wonder what that metal piece attached to the temperature wheel is? That piece is set at around 170 it seems.

Aquastat close

Aquastat full

Heating system

  • What are you trying to accomplish by changing the temperature? Mar 4, 2019 at 21:28
  • Are these steam radiators or just hot water?
    – Hari
    Mar 4, 2019 at 22:02
  • The only way to change the temperature of the radiators is to set the thermostat.higher.
    – d.george
    Mar 4, 2019 at 23:31
  • The radiators are hot water. I am not really trying to accomplish anything in particular, but if heating the water more could get the temperature up faster that could be a benefit. I'm not sure what the temperature should be even and how to check it.
    – Christian
    Mar 4, 2019 at 23:54

2 Answers 2


Boilers typically have a aquastat, high limit, low limit in one of several configurations.

This is an all in one unit specific to oil. enter image description here www.inspectopedia.com

Most aquastats look something like this on the outside

enter image description here www.ebay.com

If you have conventional radiators high limit set to 150 max is common, convectors you can go to 180. It's usually best to run as low temp as possible but with oil it's very important to maintain a minimum chimney(stack) temperature. Low return temperatures can cause acid in the chimney. Now baseboard rads are split between the two types.

This is a conventional and beautiful cast iron radiator enter image description here www.allaboutrads.co.uk

This is the inside of a fin tube convector enter image description here www.inspectopedia.com

If your baseboard rads are copper tube fin type like the convector image, you can go up to 180. If they are cast iron you should keep the temperature lower because the surface gets very hot to the touch.

If you have any pictures of the controls attached to the system they would be helpful. Just keep in mind, oil is finicky and needs yearly service by a reputable technician.


There is nothing to be gained by your idea. It is a good thought but it will result in poor heating of the rooms. If the radiators are cast iron and the temperature of the water in the rads were to heat-up quicker, that would cause an over-run of the room temperature since the rads would now have a higher temperature water than necessary to heat the room to it's normal temperature. Heating the water in the rads just enough to maintain an even room temperature will provide the best comfort. It may even produce the lowest heating bills. ( I like @Joe Fala picture of that beautiful cast iron old style decorative radiator. These were common in my day).

  • Thank you for all the information. I have no experience with these things. My radiators are not cast iron, they are covered baseboard radiators. I feel it takes a long time to heat up in the morning from 62 to 70F and the radiators doesn't feel that hot (although i do not know how hot they are supposed to feel). I do see an aquastat but it's one the water heater. That's where I set the temperature of the hot tap water. Should there be one of those for the heating system as well?
    – Christian
    Mar 5, 2019 at 15:09
  • Yes, there should be at least 1 or maybe 2 depending on the model number. The 1 on the boiler should be set at 180 degrees and may look like an L6006c Honeywell control. Looking at the picture you posted I can not see anything that looks like a limit control. If you find a limit on the boiler and it is set at 180 degrees, you could set it at 200 degrees but I don't feel it is necessary. Your system is probably working correctly and need no other adjustments.
    – d.george
    Mar 5, 2019 at 16:00
  • We do have a reputable service company check the system once a year in October. The question is, how much to they check? I will look for another limit control. Very good to know that there should be one.
    – Christian
    Mar 5, 2019 at 16:26

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