When is a LLH required over Close T ?

TAG

Have only used the close spaced T's on one project. Years ago I retrofitted radiant floor into a small writers cabin that a previous owner built on my property - used an electric boiler.

All of my older rehab projects used traditional Cast Boilers -- piped "pumping away" with the primary out to high temp radiators. Bypass with Danfoss heads on those. Radiant off of primary loop using 1.25" copper pipe w/ own pump after mixing valve.

For about the last 15 years my projects have been full floor radiant and I have always used a LLH. Since I have done a few I'm often asked about the close T's and I'm never sure when the limit is reached. 1.25" copper will take a decent flow ... but, most people who ask are wanting to do things on the cheap and that's not my goal on my personal projects.

What's the formula ? I was looking over a new purchase (relative) -- two story garage with two manifolds. 8 loops each of 300' PEX all on 1" pipe w/ the T. Not working all that well -- it's also using an "on demand". It has a few issues

EBEBRATT-Ed

I think PS can be used instead of a LLH if it is sized right. After all, Radiant heat was around long before LLH became the new thing.

LLH is also the air removal device and makes a "slow place in the road"

Just size the tees conservatively for the flow and it should be fine. No reason it wont

Robert O'Brien

Hydraulic separation is the goal, detaching flow through boiler from flow through system.

hot_rod

Two main differences is that separators can add 4- 5 additional features in addition to hydraulic separation. The smallest Caleffi Sep 4 adds almost 2 gallons of buffer, more volume than some mod cons.

If the P/S is a series loop, it requires one more circulator, and the take-offs see a temperature drop as you go around the loop. With a separator or LLH, the loads are in parallel, all seeing the same temperature.

Properly sized and piped the closely spaced tees will provide adequate separations, if that is the only goal.

Labor savings can be substantial with a 4 in 1 separator also.

GroundUp

Required? Never. From a hydraulic separation perspective, they are simply 2 different ways of performing the same task- nothing further. Whatever issues you're having with this particular system, is completely unrelated to the closely spaced tees versus a LLH.

TAG

Well it would seem to me that at some point the close T will have a flow problem ... unless you oversize it ... in effect making it look more like a LLH.

It seems the flow requirements of larger 1/2 Pex radiant system favor using a LLH

hot_rod

TAG said:

Well it would seem to me that at some point the close T will have a flow problem ... unless you oversize it ... in effect making it look more like a LLH.

It seems the flow requirements of larger 1/2 Pex radiant system favor using a LLH

Correct, even with a close nipple between the tees, there is some pressure drop. How much depends on flowrate and pipe diameter

An engineered separator will provide better separation as the barrel is much larger diameter. Caleffi uses a 3:1 ratio, so a 1” sep will have a 3” diameter. Even under maximum flow, expect less than 1/2 FPS velocity between top and bottom ports.

TAG

Hot Rod ... It's what you don't know that gets you. I'm sure there is a formula and general rules of thumb when it's best to use the LLH. When I lived in Germany they all had the LLH or that Big Buderus mixing valve thing .... so when I did my first full radiant w/ lots of loops it just seemed safer to go that route. Made piping easy as well ...

Tinman

Once I installed my first hydraulic separator, I never went back to tees. It works better, it looks better, and it saves time.