Re: Hot water system answers

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Posted by Harold Kestenholz - Hydronic Network on September 28, 2001 at 09:38:19:

In Reply to: Hot water system questions posted by Roger on September 28, 2001 at 08:11:31:

: Q1. I have an old American Standard boiler with Bell & Gosset pump. (30+ yrs) all work great but I am removing a cast iron radiator that is 16" high x 7 tubes x 15 sections.

*** The dimensions approximate 49 square feet of Equivalent Direct Radiation (EDR). At 140F, the output of the radiator is about 4500 btuh. However, the temperatures you are seeing in mild weather may not be the temperatures the system gets to in the colder weather. as the outdoor temperature drops, the system will get to higher temperatures as the thermostat calls for heat longer, so the output of the radiator can get to 8800 btuh at 180F water temperature.

the boiler only gets to around 145 degrees then starts circulating return water back in and equalizes around 120-125.

*** From this information there is a circulator control (also called a reverse-acting switch) that starts the circulator when the boiler reaches a minimum temperature. this is good, as many kickspace heaters will not turn on their fan until the water reaches 140F. It is not an economical idea to raise the circulator control setting higher, as this would make the pipes and radiators hit with higher temperature water and increase waste of energy and may cause temperature swings in the rooms. If you have a kickspace heater with this switch, it will not heat your room until the weather gets colder so the water temperature rises.

: Q3. I plan on replacing the above mentioned radiator with a hydronic kickspace heater. Any comments good or bad about doing this?

*** The existing radiator is most probably on a two-pipe system now, so the higher resistance would simply permit less water to flow through the kickspace heater and divert water to the other radiators. Most kickspace heaters have a high resistance to the flow of water, much more than radiators, so the full flow required for the heater may not be sufficient to give the heat expected unless a separate circulator drives water throught the kickspace heater or the heater has its own supply and return from the boiler & circulator.

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