Hydronic questions

[TLRobbins]

My heating system when installed in 1994 consisted of a Weil Mcclain Cast iron boiler and WM copper tube baseboard. It was sized to run 220 degrees if I remember correctly. I installed it but it was sized by my employer. It has always worked well and heated well. A few years ago I had an opportunity to buy a Navian Combi-boiler. I added the Combi to my existing system and kept the cast iron boiler in tact and use it as back up. In very cold weather since the Combi will only put out 180 degree water it struggles to keep the house warm and I will usually switch over to the boiler. My thinking is (please correct me) I could overcome this lower temp by adding more baseboard but that would require a lot more work than I want to think about and some of the areas there is not enough room to add more. Another solution might be to change the elements to Hi output elements in the existing baseboards??? Another question is, would I get more heat out of the existing system if I change speeds on the circ pumps, either slowing them or speeding them up

 

[Fitter30]

200° is a normal setting for a limit. Operating control 180. What is the input btu ratings of both boilers. Model of the Navian? 220° water with a leak the boiler water would flash to steam 7lbs of system pressure raises boiling point to 221°
Any condensing boiler for heating return temperature has to be below 140° to get the 95% efficiency above 140° drops to 87%.

 

[Sponsor]

 

[Sylvan]

200° is a normal setting for a limit. Operating control 180. What is the input btu ratings of both boilers. Model of the Navian? 220° water with a leak the boiler water would flash to steam 7lbs of system pressure raises boiling point to 221°
Any condensing boiler for heating return temperature has to be below 140° to get the 95% efficiency above 140° drops to 87%.

People do not take pressure temperature in account.

 

[John Gayewski]

So I'm doubting your system was designed on purpose to run at 220°, no one would do that and if they did they should not be designing systems. That would be output temps for steam baseboard, not hot water.

Yes the faster your circulator runs the water, the more heat you will get. There are problems associated with running the water too quickly though.

If your system isn't keeping up with the normal 180 supply temp then you need supplemental heat. Whether that is adding more baseboard or maybe some in floor heat, or maybe some radiators. A more long term fix would be to add whatever way you can.

Also you can gain a lot by adding insulation or new windows.

 

[Sylvan]

"Another question is, would I get more heat out of the existing system if I change speeds on the circ pumps, either slowing them or speeding them up"

Excessive velocity on HW can easily lead to erosion of the copper tubing NO MORE than 2 FPS over 140 DEG F

in cold water systems - the velocities should not exceed 8 feet per second

in hot water systems with temperatures below 140 - the velocities should not exceed 5 feet per second

 

[TLRobbins]

200° is a normal setting for a limit. Operating control 180. What is the input btu ratings of both boilers. Model of the Navian? 220° water with a leak the boiler water would flash to steam 7lbs of system pressure raises boiling point to 221°
Any condensing boiler for heating return temperature has to be below 140° to get the 95% efficiency above 140° drops to 87%.

that 220 design could just be my poor memory! The high limit is set at 200. The CI boiler is 105,000 the navian is a NCB-240

 

[Fitter30]

With a 200° limit the highest setting for the operating control would be 190° at best and not have nuisance trips on the limit. Navian boiler is over twice the size of your ci boiler. Have you even pulled the fin tube covers to see if the fins are dirty. Take some pics of both boilers piping and pumps.