Sizing Hydronic Unit Heater that Replaced Reznor Gas Hanging Heater

dardo

In an earlier post I mentioned installing a very rare Dining Room Radiator in a space that was previously heated with an unsightly gas hanging heater. Here is the rest of the story…… The room has been been used as a printing studio since 1919 when my grandfather opened up the second floor of the 1830's brick house with a walk around balcony and installed a skylight creating an interesting space where he and my father worked for the next 75 years. Interesting yes, but, a heating nightmare. I have pictures from 1925 showing a standard radiator and a horizontal unit heater, both being supplied by a coal fired boiler. At some point in the 1960's, they were removed (I believe after the pipes froze) and a 56,000 btu gas hanging heater was installed, vented directly into the chimney. Now that I have completed rebuilding the chimney from the deterioration caused by the flue gas, I need another heat source with more btu's than the two radiators I installed can put out (about 17,000 total). The room is only 500 square feet with a 19' ceiling, skylight and one window. My questions are: Knowing the old hanging heater did a great job, should I size it the same minus the additional radiators (56,000-17,000)? The new boiler has plenty of capacity (oversized). You might be asking why put another unsightly hanging heater? At least I will be able to position in a location not dependent on the venting and there is no room for more cast iron rads. Secondly, would it matter in what order the two radiators and unit heater are piped? They are on their own zone so I am having significant short cycling issues which I hope with the addition of the unit heater will be much better. I am looking at a Modine, unless anyone has a better suggestion. Sorry for all the verbiage but I wanted to provide an accurate picture of the situation.

EBEBRATT-Ed

Steam or water??

dardo

Water.

pecmsg

1st get an accurate heat load / loss manual “J” done.
depending on where you are a heat pump WITHOUT back up. Rather straight electric or oil / gas.

EBEBRATT-Ed

Doing a heat loss and then deducting the radiator capacity would be best.

If the rads and the unit heater are controlled by the same thermostat and will run together they will heat at different rates. As long as you can live with that

Modine has a 44,000 btu model that would do the job with the rads. Caution that their standard ratings are at 200 entering water temp and 60-degree air inlet. Their manual shows how to adjust for different air and water temps if needed.

dardo

Thank you Ed. That is what I needed to know. I really appreciate the help.