Should the circulator always be active?

AlwaysLearning2024

Hi everyone,

Learning so much here! Please forgive my newbie questions.

In a typical heating cycle with a hydronic gas fired boiler heating system, is it customary that the circulator is always running regardless if the boiler has stopped firing/heating?

Jamie Hall

That depends a little on the system setup. For the normal, plain vanilla hot water heat setup, with a standard boiler and baseboards or radiators, whether there is a primary/secondary piping arrangement or not, the circulator should be running any time the thermostat is calling for heat. Whether the boiler runs all the time or not depends on the match to the load.

At the other extreme would be a radiant heating system with a mod/con boiler — there the circulator is running all the time, period, and the boiler is running most of the time, modulating its ouput under control of an outdoor reset and a space sensor trim.

AlwaysLearning2024

https://forum.heatinghelp.com/discussion/comment/1804175#Comment_1804175

Thank you, Jamie. I should have provided more information. Yes, plain vanilla. 4 family apartment building with fin tubed recessed heating elements. Using a very "aged" Weil CG series gas boiler. Circulator recently replaced with a Taco ECM.

Is there any drawbacks aside from energy use of the circulator to running full time throughout the cold months?

Snowmelt

yes when call for heat the pump comes on , pay attention to the temperature & flame. When asking for heat the boiler turns on, the gas valve lights the burner heats the water unit it reaches what the aqustat is set for (usually 180 ) the goes off while the pump continues to spin , pumping water through the pipes. When the temp goes down to 160 ish the flame comes back on to heat the water until the thermostat is satisfied. Then both shut off.

AlwaysLearning2024

https://forum.heatinghelp.com/discussion/comment/1804181#Comment_1804181

Thank you!

Jamie Hall

The only really significant drawback to having the pump turn on and off is, oddly, noise. If the system is running all the time (and your system might really benefit from primary/secondary piping, with an outdoor reset control on a mixing valve on the secondary side, which would maintain the circulating secondary water at a "just right" temperature) there is very little expansion and contraction of the radiating elements and piping, and thus very little noise. On/off operation of the pump with nice warm water does cause expansion and contraction, and possible noise. Usually no big deal…

jumper

I believe that pumps & motors last longer if they're left on. But I have no data to show that.

hot_rod

if you circ has a delta p mode, and you use TRVs, the pump could be plugged into a receptacle. It will run and ramp up and down on its own.

wlee

I've been curious about this as well. We have an oil-fired boiler with hydronic baseboards, but also supplement with a wood stove on the lower level. In February 2023 the temps dipped to below zero with strong winds overnight. We had the wood stove lit and it provided enough heat for the boiler thermostats to be satisfied, so the circulator never ran. The result was a frozen and broken heat pipe. I thought the area around the pipe was well insulated but clearly, on that night, it wasn't enough. Anyway, I couldn't help but think if we hadn't lit the wood stove, the boiler and circulator would have been running frequently and the water in the pipes may not have been standing long enough to freeze. When the pipe was repaired we stuffed as much insulation as we could into the tight space, but have since wondered if there was a way to run the circulator without the boiler/burner on nights like that just to keep the water in the pipes flowing.

hot_rod

Constant circulation with a 3 way zone valve is an option if it is one loop, single zone.

When the thermostat calls for heat the 3 way valve moves flow from the boiler to the loop,

This is how I run my shop.

GrafHeating

I do mainly retrofit systems on homes nearing the 100 year mark. Most of these would not absorb the cost of removing and replacing all of the overlarge piping designed for gravity flow.

In a gravity system the flow is somewhat regulated in that the coldest rooms create the most convection in the system. This flow changes as the sun goes to different parts of the house during the course of the day.

Adding a circulator , at all, changes this. The flow follows the course of least resistance.Any one of the large cast iron radiators with accompanying large piping can handle the full flow of the circulator. The end result is overheating the room with the least resistance. Eventually everything warms up , but it takes a while.

Running the circulator constantly mimics the gravity flow that the piping was designed for.

The system as a whole warms uniformly with a bit of preference for the coldest room. Not quite the same but close to the original design parameters. Most of these radiators are also far larger than required so as the water warms the tstat gets satisfied and the radiators still disperse heat at ever decreasing rates, until the building heat loss causes the boiler to fire again. This again mimics the firing rate of an automatically fired boiler gravity system. The boiler may not ever see cold system water all season.

This field tests out to be more efficient than one might assume. Requiring far fewer bells an whistles than trying to micromanage flows to multiple zones there are fewer things to fix later on .The system just wants to function correctly. This plus the initial cost savings on installation make it an attractive option.

I have used this successfully wit most cast iron replacement boilers and condensing boilers.

On the condensing boilers I usually do primary secondary piping running the system circulator 24/7

hot_rod

https://forum.heatinghelp.com/discussion/comment/1804502#Comment_1804502

Adding TRVs could take that gravity conversion another step, allowing the rooms, or even radiators to have temperature responsive control. Comfort and energy savings.

Or dynamic balancing valves at each radiator, if you calculate the room by room load and determine the radiator EDR, with delta P circulator.

I suppose it always comes down to the budget question :)

Dave Carpentier

@GrafHeating I wonder what affect a delta-p circ would have ? A slower velocity would reduce the flow resistance in the skinny loops ?

hot_rod

https://forum.heatinghelp.com/discussion/comment/1804522#Comment_1804522

A delta P circ needs to see varying flow requirements to ramp up and down. Electric zone valves, manifold actuators or TRVs. As any of these open and close or modulate in the ase of a TRV, the circ responds.

And it needs to be constantly powered, spinning to respond with TRVs for example, since there is no end switch.