Grundfos Variable Speed Pumps?

[Peteman]

I currently have a Grundfos UP15-42F recirculating pump on my boiler. There are 3 branches (all on the same zone) throughout the house. The branch with longest run and the most radiators does not get near as warm as the other 2 branches when the heat is not on for very long (> 60 min as when the call for heat is only for about 1 degree increase during the day). I was wondering if switching to a Grundfos UPS15-42F (same as original but 3 speed) or a UPS15-58FC (3 speed also) would make an improvement in pushing more flow through the system (pump curves for those show about a 3-4 ft head improvement at similar flow rates). Radiators have been bled several times (no additional air after first bleed in the fall). Thanks.

 

[Dana]

This sounds more like flow balancing problem than insufficient total flow. Are there globe valves or ball valves or some other flow balancers on the branches for tweaking the individual branch flows?

 

[Sponsor]

 

[Peteman]

Hi Dana - yes there are older style brass valves that control branch flows (diamond shaped heads - cone valves I believe). I set the one that has the long run wide open and the others about half way. This improve things but I wondered at what cost? With the branch to the room where the thermostat is located being only half open, it seems that the boiler will have to work harder to keep that thermostat satisfied. When I first moved into the house, all three valves were wide open and the long branch would only get warm during long burns - in fall/spring they barely would get warm (when burn times were short). I thought that perhaps a more powerful pump would be able to overcome the larger head requirement of the long branch.

I tried to call Grundfos to discuss options but, not being a heating contractor (no account), they wouldn't talk to me. They gave me a phone number for a local supplier but they only seem to be able to take an order on a customer specified pump - no advice.

 

[Dana]

The heat loss of the house is the heat loss of the house. Tweaking the flows for temperature balance may, "... the boiler will have to work harder to keep that thermostat satisfied...", but only because it raises the temperature of the under-heated branch rooms.

The same would be true if simply pumping harder raised the temperature of that branch too, but you'd be spending more on pumping electricity.