One Pipe Convector

bml207

My house has an addition that was put on much later than the rest of the house. Instead of using a cast iron radiator like those in the rest of the house, they added a fin and tube convector. That room tends to be colder than the rest of the house because the vents on the radiators are relatively fast so the convector doesn't get much steam and the cast iron in the room with the thermostat keeps the boiler from firing while the addition cools down. The problem becomes more noticeable the colder it gets.



Currently, it is vented with a Hoffman 45 (a 41 clone, just a different thread size). Is this the fastest I can vent it? I would prefer the addition to be slightly warm while the boiler fires and then slightly cold right before the next cycle, rather than having it be sightly cool when the boiler fires and several degree too cold before the next cycle.



Thanks.

icesailor

Old Timers:

The old timers always told me to never mix cast iron radiators and fin tube convectors on the same zone. The fin tube zone will never work properly.

Your problem confirms that they were right.

BobC

Was it sized right from the get go

Is the pipe feeding this convector sloped properly and is it insulated? A convector like that just doesn't act the way cast iron does and it's possible that convector was never properly sized in the first place, especially if the addition has 3 sides exposed to the outside.



You could try a Hoffman 1a adjustable vent on that convector and see if it helps. Also make sure the convector has some slope to allow water to flow out once it's condensed out of the steam.



Bob

bml207

Size

I have no idea if it was sized right when they put it in. It's been here for many years.



There is insulation and good slope on the run out. There is some slope on the convector element and I don't have issues with hammer. How much slope is ideal?



I think the vent is just a little slow, and, as you say, the behavior of the low thermal mass convector just doesn't play well with the cast iron. I just don't want to put too fast of a vent on it as the convector element piping is quite small and over-production of condensate might be a problem.



Thanks.

BobC

how much

If the pipe feeding the radiator has a slope of 1in 10ft that should be enough for single pipe steam, the convector just needs enough slope to encourage the water to run out.



This may take some experimentation and that is why I suggested an adjustable vent. The hoffman 1A is a little sloppy so precise adjustment can be a problem, if you unscrew the top you'll see what I mean. Another option would be the Maid O mist that comes with 5 different orifices so you can select the rate you want.



If the Hoffman you have is equivalent to the 40 it is rated at 0.042cfm  at 1oz, the 1A can be adjusted from 0.02 to 0.145cfm while the maid O mist runs from 0.028 to 0.341cfm. i agree that you don't want a very aggressive vent on the convector.



Bob

Hap_Hazzard

Reduce temperature swing.

I have a similar situation. The convector is about 8 ft. long and is in front of a big bay window, so I'm looking for a cast iron window radiator, as low and wide as possible.



To make things more livable in the meantime, I have set the temperature swing on my thermostat to 1 degree. This will give you shorter, more frequent cycles, which isn't ideal, but it does allow the heat to come on before it gets uncomfortably cold in the room with the convector.



Check the manual that came with your thermostat for instructions on adjusting the swing setting. Most thermostats allow you to adjust it, but it's not something most people know about.

bml207

Swing

I think the swing on my thermostat is set to 0.5 degrees, but 1 CPH. Maybe 2 CPH would be an improvement?

jumper

how about slower vent on CI ?

Starting with room with thermostat ? It can help but generally fintubes cool sooner.

bml207

Vents

I'm hoping that I can get away with a slightly larger vent on the convector since I don't want to change the vents on the rest of the cast iron radiators in the house (again) if I don't have to.



The real answer to my problem is probably to get a cast iron radiator and replace the convector....

Mark N

Convectors

They do sell cast iron convectors. I think governale sells them

Hap_Hazzard

CPH

I'm not sure, but I don't think my system cycles more than once an hour even when it's cold outside, so you might find increasing the CPH doesn't do anything, but it's worth a try. Keep an eye on your pressure though. You don't want the boiler starting up before your main vents cool down enough to open.

bml207

CPH

You're probably right; I suspect the boiler won't fire any more often than once an hour no matter the setting. There are two large cast iron radiators in the room with the thermostat.



My mains are lightly enough insulated (about 3/8 inch of the 'miracle material') that the main vents open quickly so that won't be an issue.



Thanks.