What is the correct temperature for a Hydronic Convector?

Red955i

Hi...I have a '50's home with single pane steel casements. Never very efficient. Two family. Two separate Weil McLain CGM-3-P1 boilers. Shows 70,000BTU/hr then under DOE shows 58000 BTU/HR... Downstairs boiler heats 1250SF on first floor plus 1250 sf basement up to low 70's. Upstairs is a 1 bedroom 850sf apartment with attic above. Always went into low 70's as well. Now will not. Boiler set to 190 degrees. Thermostat kicks on boiler it heats water to 190 goes off. New circulator. Convectors when covers are removed and IR gun aimed at pipes inside fins shows approx 125F on all four convectors. So I dont seem to lose temp in the short loop up there but I'm losing 65degrees from boiler up to second floor. Is my convector temp too low? or is there some other problem going on. Ive replaced the circulator and all air vents... Thanks Bob

Jamie Hall

Sounds wacky, but what's the pressure in your system at the boiler? It sounds as though you are not getting good circulation to the second floor, and I'm wondering about an air problem.

pecmsg

Infra-red thermometers are very inaccurate. Place a couple inches of black electrical tape on the pipe and check again.

Measure the temperature at the boiler supply and return.

Red955i

Thanks...Boiler pressure is 20psi...Circulator is new....air vents on all convectors are the auto vents, which are new and have been manually vented to start...Not sure how to do the electrical tape. The 125 degree temp I mentioned was shooting the three pipes between the fins built into the convector.

pecmsg

The copper pipe is the problem. Place black electric tape on the supply and return pipe at the boiler and take the readings.

Red955i

Ok I did that with black electrical tape and agree that the IR gun gets a wide variety of readings. Not sure what better way there is to read these temps. The one constant I can see is that the difference between what's leaving the boiler and what's returning to the boiler is between 38 to 40 degrees. The outside temperature is 18 degrees with a "real feel" temp of 5 degrees..Not sure what the difference means. Boiler has only one setting (not on and off) and has a larger pointer at 190 making me believe that is the manufacturer preferred setting...thanks

pecmsg

IR thermometers are affected by color, material, distance several different things, that's why there not accurate.
What were the temperatures in and out?

Red955i

161 degrees out 1 foot from boiler... 123 coming back 1 foot from circulator

Red955i

Boiler set at 190 but was running and showing 180 at time of reading with 23psi

Jamie Hall

Regardless of the vagaries of IR thermometers -- and they can indeed be tricky -- that much temperature drop almost has to be a flow problem in that circuit somewhere. Air is the most likely problem, as your pressure sounds adequate (assuming the gauge is sort of accurate), but could be as simple as a valve not open all the way.

Red955i

All the valves for the convectors are open, all the air vents have been replaced. All have been bled, then set to auto. Oddly....all of the center tubes (there are three) in each convector element have the same temperature give or take 2 degrees. So there is no real drop from radiator 1 to the last #4. Circulator is new. System was drained then bled to change circulator & vents, but problem existed prior

Red955i

We have city water pressure which is about 50-60psi. System has a reducer to lower that pressure

Jamie Hall

Bled, yes. But properly purged?

Red955i

Jamie that's a great question. Please enlighten me and I will tell you if I did it properly. As I mentioned before, I had this problem before I replaced the circulator. So when I replaced the circulator, I shut off the thermostat, the boiler power and shut off the supply, I attached a hose to the drain below the circulator and opened the drain. As it was almost finished draining I went upstairs and removed the air vents from each of the four radiators (convectors), I then removed the one from the boiler. With the system now empty I replaced the circulator, then all the vents. Then I closed the drain and removed hose. I then turned on supply which began to pressurize system. I went upstairs and held the vent open on the one closest to boiler till water came out, then then next, the next and the next. As each finished I tightened the cap. When the air was out of the furthest one, Set it to auto, then went back and set the other three to auto. Then I went down and turned on boiler, then back up to turn on thermostat. After it ran awhile I manually bled them again. If that is incorrect please let me know...Thanks for your help!

mattmia2

Did you leave the caps loose on the automatic air vents?

You still could have a pocket of air somewhere that can't make it to a convector by gravity alone.

Red955i

Yes the caps are loose in the "Auto" mode. I even made sure the vent side of the convector was uphill from the other side

archibald tuttle

when you say manually vented, do you have 'coin' vents in addition to automatic? On our convectors I replace coin vents with 1/8" ball valves and short nipples so I can bleed into a bucket. if the near boiler piping is the original you usually don't have isolation from the boiler and relief so you can purge at higher than 30 psi.

don't try this at home, but i do all my temperature checks by "hand", i.e. be cautious, touch pipe lightly so as not to burn your hand if it really is 190, but as everyone suggests, with decent circulation your feed and return should be closer in temperature. And if you turn off the boiler for an hour and then turn it on, you should feel a flush of cold water coming down the return.

Are these convectors piped off off tees or venturie tees in the basement which is a lot of up and down, more potential for air, or through piped just beneath the 2nd floor?

It's a weird problem if you are getting ghosting circulation because with an airlock you usually get none. Other possiblity is the circulator is not actually working even though its new and you are thermosiphoning very slow circulation to see the slight heat that you are. Does the circulator have isolation valves? I'd pull it and bump it on and make sure it's actually turning.

my 2¢. you can send the check to . . . :-) good luck. post results

brian

Red955i

Brian....first...I know very little about this....which is why I am baffled. The auto valves are float valves...you can manually bleed them by pushing down on the shrader valve until you get a steady stream of water. I put towels all around and let it spray a lot of water to make sure all the air was out. If you let boiler cool and then fire up you can hear the circulator run AND feel the water moving in pipes before they get too hot to touch. I cant tell much else as all the pipes except right over the boiler are covered by ceiling. The uninsulated pipes run around the basement ceiling so the uninsulated run to each convector and back goes from basement ceiling to 2nd floor and back. These are long, but straight vertical runs. There are only 4 convectors on the circuit. The bath is a short one, the other 3 are maybe 36 to 40" long. They have three pipes in them between the fins. When I tested these with the IR Gun I got about 125 degrees (+/- 2) in each of the 4 center pipes. I had no idea how hot the convector should get? And as noted the IR gun may not be super accurate. With a boiler set to 190, the boiler running and the boiler temp gauge showing 180 the pipe leaving boiler shows 161 degrees. So if you believe the gauge and IR I've already lost 19 degrees 1 foot from boiler. By the time it hits first convector, which come off the loop straight up from boiler, im at 125 degree (makes no sense), last convector is still 125 and return back at boiler is 123. With thermostat set at 70, Apartment will only get to 62 degrees as measured by thermostat, IR gun on wall at thermostat and separate thermometer (all agree) Thanks