How Does a Primary Loop Loose BTU's?

ced48

Where do the BTU's that the primary loop looses in a primary/ secondary system go? If the water moving thru 10 or 20 feet of pipe in the primary gives up this much energy, wouldn't the returning water in a secondary heating circuit be stone cold bt the time it returns?

Eastman

what kind of configuration

are you visualizing? 

Jamie Hall

The only way

BTUs are lost in a primary loop is by heat loss through the piping.  If you have enough piping, you could lose some, I suppose... Think about this... where's my coffee?... say 1" pipe, that's one square foot for four feet of length, more or less... so, uninsulated and running at 180, you might loose somewhere around 50 BTU per foot from the pipe.  Which isn't a whole lot.  Now if you are worried about that amount of loss, insulate the pipe...



Don't confuse the heat loss from a pipe with the number of BTUs that size pipe can deliver.  Two completely different measurements.

ced48

Okay, Just Not Thinking Straight

The boiler will bring the loop up to design temp quickly, remain off for a fairly long time because of little heat loss, and than fire for a short period again. This does make sense- Thank you

chapchap70

If you have a conventional boiler...

A boiler that maintains temperature will fire when the water temperature falls 10 degrees below the low limit aquastat setting if there are no other calls for heat or hot water.  The burner will stop firing when the low limit is satisfied.  Since there is no load, the burner run time will be short.



BTU's are lost when the boiler is idle because there is nothing preventing the heat from radiating out the chimney.  Less BTU's are lost into the boiler room through the jacket.  Depending on the outside temperature, (more are lost when it is cold) a couple hundred BTU's per hour are lost when the boiler is idle.  I hope this answers your question.