What is the air temp coming off a typical steam convector?

The Steam Whisperer

I'm trying to work out how much energy is saved by insulating the back of convectors. Steam is out of season right now, so I can't just go and take a reading.

EdTheHeaterMan

somewhere between hot and very hot, but not extremely hot.

Jamie Hall

Good answer! I've never measured it either, but it's nice and warm. If you put something back there, make sure you don't interfere with that air flow. You may do just as well with a simple reflective sheet on the wall in back.

dopey27177

That is hard to answer.

Firstly the convector needs to be 1 to 2" off the wall.
The temperature of the air coming off the convector depends on the steam pressure in the system.
Assume 1 PSI steam where the temperature of the steam is 215 degrees the high end temperature when the the room is at 70 degrees could reach 180 degrees. That temperature drops quite quickly more unto about 155 degrees because of the air circulation caused by the upward draft. thee temperatures can different from manufacturer to manufacture because there maybe different densities to the convectors.

OH by the way don't put your hand on the convector it can get pretty close to the steam temperature.


Jake

JUGHNE

Hot enough to melt crayons stored in the cabinet in front of the convector.
This was the case when someone removed the cover and enclosed the unit and made no access for lower air flow into the fin tube.

After drilling about 75 or so 1 1/2" holes in the toe kick it now waves the flag hanging 5' above.

Not much help am I?

Unless you know the melt point of today's safe crayons.

EBEBRATT-Ed

I know Base Ray used to recommend insulating behind their CI baseboard with reflective insulation

The Steam Whisperer

The convectors are built in to pockets in the exterior walls of my church and I'm sure we're loosing a good amount of heat out the back, sides and top. I know that this insulation is near the top of New York City's recommended improvements for steam systems, but I like putting payback numbers with improvements.
Dopey, so it sounds like probably about 180F in the cabinet dropping to about 155 once exiting the cabinet. That gives me about about a 155F delta tee between the cabinet and the outside temp. The wall is probably about R-2 at this thinner location. Assuming about a 50% on time on a typical day with a fintube element, the average temp in the cabinet is probably around 112F, delta tee of 92F. That's a heat loss of about 45 btu/sqft/hr. I have about 7 sq ft of exterior exposure above the element in each convecter, so that about 315 btu/hr per convector x 24 hours a day = 7560 btu/day per convector on typical winter day. 11 exposed convectors per day is 83160 btu/day or about a therm per day of gas usage at 25F outside. That's a lot of gas over the heating season. I've got to work out the therms per year, but this looks like a worthwhile project even with us keeping the building at 45F (in Chicago) about 6 1/2 days a week ( about a 30% reduction in heating needs compared to keeping the building at 70F)

dopey27177

To Steam Whisperer:

Remember this When pulling the convector out to insulate and put reflective foil over the insulation you need to keep a space of 1" minimum to 2" from the adjusted wall.


Jake

ethicalpaul

I really don't like those pockets. Your calculations look good. Here's my un-asked for suggestion: Pull the convectors, fill the space with insulation and install radiators!

The Steam Whisperer

I was just figuring on lining the inside of the cabinet with 1/2 inch foil faced foam (r-3 not including the relective surface), beveled where it meets the element. That 1/2 inch probably will provide no more restriction to air movement than the fins themselves.


No room for radiators unless the pews are shortened. The side aisles are barely 30 inches right now. I would prefer rads too, but I orificed the system and the boilers are staged by the thermostat. The convectors are only partially heated most of the winter, so there is probably a lot less hot air sitting at the ceiling than when they ran full on/full off with much more stable temperatures. Not quite like full hot water outdoor reset, but approaching that.

mattmia2

I bet those pockets are poorly sealed, I bet your loss due to infiltration is far more that through conduction.

The Steam Whisperer

It's solid masonry construction so air leakage from the exterior is nil.

mattmia2

Unless they did a really good job of the inside of it there usually are gaps where the bottom of the opening meets the floor and at the top. If it is block of some form the cores are usually wide open. There is also where the piping enters the space. This could be atypical, but my experience with such openings is that they put no effort at all in to doing anything other than making the hole big enough to fit the equipment in.

The Steam Whisperer

Thanks for your mention of the block cores.. forgot about that. The church sanctuary is quite an unusual construction that probably slows the convection patterns in the block cores.....Random Ashler decorative concrete block interior walls with Random Ashler stone exterior.
A little spray foam around the perimeter of the housing should seal that up pretty well. Fortunately the fitted stone exterior should stop any direct exterior air leakage.

The Steam Whisperer

It seems that typical foam insulation boards available cannot be left exposed and may degrade at these temperatures. It looks like fiberglass or mineral wool board or duct insulation are my only alternatives.

mattmia2

I was wondering about that but I assumed you knew what you were doing with the foam. You could put drywall or cement backer board over it as a fire barrier if you really wanted to use foam but fiberglass/mineral wool board is probably more practical.

The Steam Whisperer

Looks like I am just going to use duct liner insulation. I might try to adhere a layer of heavy foil on top of the insulation to create some reflective surface and make it smoother for airflow. I bought a roll of duct insulation years ago and keep using it up a bit at a time. I insulated all the interior panels for my work van....you now have to keep the heater on low even when its 0F or it gets too hot. Did my 1998 escort wagon too along with some other materials for insulation and sound deadening. The car is much cooler in the hot weather with a lot of the solar heat no longer making it inside.