cast iron baseboard minimum supply temperture

johntrhodes81

On a modcon system with cast iron basebord. What is the suggested minimum temp for supply? Right now i am using 115* for minimum temp for odr. Should i go lower? What temp will the radiation stop?

Thanks for the help.
John

Leon82

If you want the lowest possible drop a few degrees at time untill it struggles to keep up with the heat loss.

johntrhodes81

Right but i can drop the supply temp and the outdoor temp it is associated with. What minimum do most suggest for ci bb?
Thanks.
John

Brewbeer

It really depends on the heat loss and the length of your baseboards. If you have a well insulated house and lots of baseboard, you can go pretty low. I'm heating with fin tube baseboards and use supply temps in the 90s when it's in the 40s or 50s outside. Heat output of my baseboards drops noticeably at supply temps below 95F.

Paul48

I think it should be noted, that, at any temperature above ambient, there will be an output. That's not to say it will be sufficient to maintain the temperature in the home. I think the best way to establish the curve is the way that SWEI always described. Crank the thermostat up as high as it will go, and begin changing your parameters until the temperature in the home is maintained. It may take weeks of tweaking.

Jean-David Beyer

"It really depends on the heat loss and the length of your baseboards. If you have a well insulated house and lots of baseboard, you can go pretty low. I'm heating with fin tube baseboards and use supply temps in the 90s when it's in the 40s or 50s outside."

For sure. I have lots of fin-tube baseboard upstairs in my house and a mod-con boiler with outdoor reset. 14 feet of Slant/Fin in each of two rooms. (They used to have three feet in each room, which was too small.) Slant/Fin have tables that show how much heat will be delivered from their products based on the difference in temperature between the supply temp and the room temp.

For example, here is the listing for my baseboard (yours will surely be different):

http://www.slantfin.com/wp-content/uploads/2015/11/BaseLine-2000-Ratings-514.pdf

When it is 50F or higher outdoors, I put 120F water into the baseboard; when it is 0F outdoors, I put 150F water into the baseboard. The 120F was picked because that zone does not have a lot of heat loss and my boiler will not modulate low enough to prevent rapid cycling. So I run it hot to get it up to temperature and satisfy the thermostat fairly quickly when it is warm outside. As it gets cold enough outside, the boiler can cycle much more slowly.

As Paul48 said, any temperature above ambient will deliver some heat. In my radiant slab heated zone I put 80F water into it until outdoor temperature gets below 50F, and increase it to 130F if it gets to 0F outside; since design temperature around here is 14F, that hardly ever happens.