Boiler Pressure and Temp

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What temp and pressure do you guys run your boiler systems at? I know there are different types of systems, just trying to learn a little more.
 
No pressure on mine, run it at 155 blower comes on, goes off at 175.
 
All kinds of variations between boilers, and systems & houses.

I would run my boiler only as hot as it needs to be to maintain the heat in my house (hotter boilers waste more heat in standby or up the chimney - some efficiency loss), and only with enough pressure to get & keep the water flowing to the highest spots in my system without creating air locks.

The key to temps is you should maintain return water at or above 140. Without return temp protection, that might mean 160-170 supply. For our place, I like to see pressures between 10 & 15 over the varying temps, which gives a good safety cushion to the blow off point.
 
Interesting!

I spoke to the guy who designed and installed the system for my father back in 1981. He said it was designed to be run at 170-180 but he runs the similar system in his own house at 200.

Our gauge runs at 20-30 lbs pressure.
 
Interesting!

I spoke to the guy who designed and installed the system for my father back in 1981. He said it was designed to be run at 170-180 but he runs the similar system in his own house at 200.

Our gauge runs at 20-30 lbs pressure.

System design plays a very big part. If the whole thing was designed for 180 water, that's what they would use to size emitters (baseboards etc) with. So if that dropped to say 160, it might not keep your house warm. Which in most or a lot of cases, could be rectified by simply putting more rads in later.

I think they used higher design temps in the olden days, I wouldn't likely use higher than 160 today. (I'm not a designer though). The amount of heat that goes up your chimney just from the boiler sitting there at 180° 24/7 is big wasted heat. Plus, a cooler boiler would have a bigger dT at the heat exchange surfaces so it can pull more heat out of the exhaust stream when the boiler is running.
 
System design plays a very big part. If the whole thing was designed for 180 water, that's what they would use to size emitters (baseboards etc) with. So if that dropped to say 160, it might not keep your house warm. Which in most or a lot of cases, could be rectified by simply putting more rads in later.

I think they used higher design temps in the olden days, I wouldn't likely use higher than 160 today. (I'm not a designer though). The amount of heat that goes up your chimney just from the boiler sitting there at 180° 24/7 is big wasted heat. Plus, a cooler boiler would have a bigger dT at the heat exchange surfaces so it can pull more heat out of the exhaust stream when the boiler is running.
Right. This system was designed in 1981 when boilers were inefficient because propane was cheap. And with the wood boiler linked in, efficiency matters even less.
 
I've messed around with my settings a bunch. My father is from the school of keeping the temp as low as possible , runs his engines at half speed, etc., so he is always egging me to run my temperature settings lower. With that thinking I have run as low as fan on 145 deg/ fan off 155 deg giving myself a bit of room from 140 deg for down side overshoot. The house has a hydro-air system and I found the air handlers did not run well at the lower temperatures. I could see how these lower temps could work with a radiant system. For the house alone with air handlers I found I liked 180 deg fan on/ 185 deg fan off. The air handlers liked the hotter water and the 5 deg differential helped keep the boiler heat transfer tubes cleaner. Now that I have added in the 4200 sq ft barn with radiant I had to lower the range to 175 deg fan on/180 deg fan off as I was getting to much upside overshoot under heavy load on cold nights. My boiler is an open system.
 
i have an old wood oil boiler .its set at 180, but at 190 the over temp switch turns the pump on. i also have a 3 speed pump that I can change when needed. psi moves around, when really hot it will read 20 to 25 psi. most of the time 12 to 16 psi.
 
Pressurized at about 12 psi, on the low side. Boiler will heat up to 200'f. With approximately 950 gals. Of thermo storage, I let it run for 8 plus hours, then "coast" for a day or more. Kinda like this photo.15743975759744395376430266256603.jpg
 
The cool part is that I have a motorized mixing valve, that constantly mixes water temp, for my heating zones, depending on the outdoor temps.
 
Mine isn't pressurized. I set it at 170 and 180 9 years ago when I got it and haven't touched it since.
 
So you're heating the water then cooling with cold water to lower the temperature if there is less demand?
15744399849824680805713159516912.jpg
Yes, mixing the 'cooler' return water. 140' is the hottest and 95' is the coldest, that is when the propane boiler takes over.
 
So you're heating the water then cooling with cold water to lower the temperature if there is less demand?

Usually the supply temp is lowered all the time, to meet the design temps, with something like in-floor. No matter what the demand is. Sending 180 water into a floor can make bad things happen to your floor. With other things like rads, I think it aims to make it just hot enough so that it will keep the house warm enough, with a steady flow. No start & stop.
 
I need to look into this mode of operation. To me, this sounds like an energy waste. Using fuel to heat water only to cool it back down. I'm sure there is sound thinking behind it. just have to understand it. Why would you not just produce the water temperature that was required?
 
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