Low limit setting question

the aquastat should be set for cold start. it is currently set for warm stat which you would only need if you had a tankless coil which you don't.

If you don't have a tankless coil in the boiler for hot water, it is always preferable to operate the boiler as cold start. It only starts and climbs to the setpoint when the thermostat(s) call. Otherwise it does not run.

Also, the "plumber" probably will set the limit at 180°F. Tell him to lower it to 165°F and see how it works out for you. Be sure to have him show you how he lowered it to 165°F. Ignore any crying by the plumber that it won't heat the house and you will be cold.

In the shoulder seasons, you probably can lower it to 150°F.

It all saves oil………..a bit at a time.

Just for your own info………….he installed a boiler that is capable of heating a 6000 square foot house when the outdoor temperature is 0°F. If you have a typical building with 2500 square feet, this boiler is way too large and will cycle endlessly.

I can't wait to hear the response.

Predicted: No Mr. Jakamini, this is the proper size boiler for your house. Those people online don't know WT-F they are talking about. I have been doing this for 30 years and NOBODY ever complained about a boiler being TOO LARGE for their house.😫

Find your thermostat instructions and make sure the differential, or swing, is set to 1.0 degrees minimum. If set lower, boiler will also short cycle, which is inefficient. You want long boiler runs spaced as far apart time-wise as is comfortable. I have the differentials on our ecobee set to 1.5 degrees, and with a similar system (oversized cast iron boiler, cast iron rads) our boiler runs about 45 minutes at a time, with about 3-4 hrs between runs (in Boston area).

And if it makes you feel better, our boiler is also 3x the size we need.

This poster has another thread with a pic of the near boiler piping. I can't be sure but it does look like there is a bypass.

Grossly oversized.

Is the aquastat the Hydrostat 3250 Plus? If so, read the manual. Use every fuel saving option it offers. It does have condensate protection, but it needs to be activated.

Your heatloss on the coldest day of the year is conservatively estimated at 70,000 BTUH. Others will suggest LESS!

So you have to ask this plumber why in the hell he would install a boiler that can deliver 158,000 BTUH!

It's going to be very difficult to manage this boiler and gain the efficiency you deserve.

Presuming he's NOT going to change it to a smaller boiler:

Ask him if he has a combustion analyzer and knows how to use it. If so, ask him to do the following:

Change the nozzle to 1 gallon per hour.

Use the combustion analyzer to verify proper CO, and CO2 readings, stack temperature (must remain over 350F), and perform a smoke test on it.

The boiler is still significantly oversized after this change but every little bit helps.

Well, that is a good start. The net output of the boiler is now approx. 102,000. Not the 70,000 that you need but manageable. See if he has any readings from the combustion analyzer (if he has one) when it was installed.