Constant circulation

HeatingHelp

Here's what you need to consider with a hot-water system running on constant circulation.

Read the full story here.

Mad Dog_2

Very thorough explanations...Thanks guys. Mad Dog

Rich_49

That should clear up some things for the masses.

Dennis1679

Great explanations, but it doesn't always have to be that complicated With proper heat emitter sizing, the boiler protected and/or installed as a secondary loop with temperature reset and maybe inside temperature feedback if the control allows, constant circulation is the quietest heat and remains the most comfortable. This works best in smaller houses, with not too many zones so that the primary zone is always on, and TRVs or Zone valves are used to prevent overheating of some smaller areas. The key is proper sizing. With a mod con, there may be no lower limit to the system temp, but in the houses I have done this to (including my own) I usually make it 100 or 110 if it's baseboard, as lower than that doesn't seem to do much..
You do give up all that crazy control, but with proper sizing who needs it?
You don't need any complicated controls. I've installed quite a few Knights with ZVC relays to switch the small zones on and off with no calling of the boiler needed. You wouldn't really need a ZVC relay, but the electricians like them
The main zone controls the call to the boiler.
The key is smaller houses, and proper sizing.
I learned this in the 80's at the IBR school, so it's nothing new and not necessarily a European idea. It makes the house quiet and comfortable all the time.
I do now use Delta T circs, but I installed plenty with 007s. No deadheading with the main zone always open

Paul Pollets

Excellent commentary on how constant circulation works. I've been using this method for over 25 years and haven't used conventional boiler controls since 1997. Never had a complaint that a customer's home was too cold or hot. Most commented that the home had used 30-50% less fuel. Since the boiler of choice was Viessmann, it was always set up to do CC. The only difference over the years was the PBD wasn't needed when a "smart" pump was being used. I learned from Bernd Giese, a retired German pipefitter who ran the Western Canada Viessmann office. He made it easy to understand and I'm fortunate he did.

Rocky_3

I've essentially obtained constant circ in my home by utilizing tekmar controls and thermostats. I have a conventional oil boiler and zone valves controlling 5 zones (two radiant underfloor with aluminum heat transfer plates, and three utilizing Runtal baseboard). All zones are supplied heat from the boiler via variable speed injection mixing. The living/dining/kitchen zone (radiant plates) is the hardest to heat so it has assumed the "controlling" zone duties. With the indoor feedback feature of the tekmar t-stats, and a deep outdoor set-back curve on the tekmar boiler control, the tekmar system has "learned" how to maintain the setpoint of the living room; no more, no less. With the variable speed injection, I can mix the supply water down to very low temps if needed and not worry about boiler flue gas condensation. By varying the supply water temp with VSI, my living room zone never quits calling for heat, yet never overheats. I always come down the stairs and step on a nice, warm wood and tile floor. Nothing like it on a frosty -40 below morning here in Fairbanks, AK. My wife thinks I'm a freakin' genius. Don't tell her different….

Mad Dog_2

We won't say a word....mad Dog

Rich_49

Oh HEAT ME .