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# Radiant Loops One or Two

Member Posts: 8
Adding radiant to a room that never had it before.  Already have 4 radiant zones in the house and have a 5 zone manifold.  Boiler is plenty big to handle it.  All good, right, Maybe not according to my plumber.

The plumber says that based on his heat loss calculations, i need over 400 feet of pex in that room.  As such, we need to have 2 loops service that room.  Poorly insulated and lots of glass.  Makes sense, the room is always really cold.  Going to install porcelain tile over mud.  pex will be imbedded in the mud.

I only have one zone left on my manifold.  The plumber tells me that he cannot simply run 1/2 pex from the manifold and tee it off to the two loops.  I am not a plumber and i have to rely on his expertise, but his explanation was lacking.  Can someone here explain to me why he cannot run a single supply and a single return off the manifold and then tee each of them so that it can feed two separate loops in the floor?  he is running 1/2 pex in the floor as well.

He is suggesting a new manifold that can accommodate the two feeds to this room.  Of course this comes at a price and a lot more labor.

Can someone explain the logic?

• Member Posts: 7,356
what else is on that manifold

and what size line is feeding it?

Any way to upgrade the glass, or install some thermal window treatments?
• Member Posts: 8
Manifold

The manifold feeds four other rooms, all with 1/2 pex.  The fifth zone on the manifold is presently capped and is unused.

1/2" pex would feed the new room.  My question is

I only have one zone left on my manifold. The plumber tells me that he cannot simply run 1/2 pex from the manifold and tee it off to the two loops. Can someone here explain to me why he cannot run a single 1/2" supply and a single 1/2" return off the manifold and then tee each of them so that it can feed two separate loops in the floor? he is running 1/2 pex in the floor as well.

He is suggesting a new manifold that can accommodate the existing four zones as well as the two new feeds to this room. Of course this comes at a price and a lot more labor.
• Member Posts: 7,356

is that depending on how much flow the existing manifold is currently handling, there are three possibilities:   The unused tap on the existing manifold may be able to handle both new loops just fine.  It may need replacing with a larger manifold.  It's also possible the supply pipe is already maxed out, in which case replacing the manifold will not help.

The number of taps on the manifold is not the determining factor.
• Member Posts: 8
feeding manifold

3/4 pex feeds manifold. Comes off of a mixing valve. Water temp into manifold is around 120 degrees, but that can be adjusted.

How do we know.  My plumber (over the phone) just said that the manifold would need replacement.  It is a plastic manifold with terra-fin actuators.  Which he hates and wants to change to stainless steel.
• Member Posts: 7,356
flow rates

are the determining factor, and those depend on heat losses in the other areas served by the manifold.

Ideally, the mixing valve should be motorized and controlled using an outdoor reset curve.  Are there other types of radiation in the house (radiators, convectors, or baseboard)?  What kind of boiler?
• Member Posts: 8
mixing valve

The mixing valve is manual.  It is a set and forget type thing.  I dont know if an actuator could be attached to it.

Burnahm boiler.  85% efficiency (i think).  Regular boiler.

No other heat source. Boiler feeds radiant zones in house.  This room is an existing porch that we are converting to living space.
• Member Posts: 7,356
how big

Is the house, and how big is the boiler (BTU/hr input rate)?  Where is the house located?
• Member Posts: 8
location

Northeast

1900 square feet

BTU 150k  +/-
• Member Posts: 7,356
boiler is oversized

63 BTU's per square foot.

12 GPM will never fit through a 3/4" pipe, and I doubt they designed it for a 30F ∆T.

You should seriously consider getting a real radiant pro to evaluate your system and make recommendations.  You can stage them if money is tight, but you need a plan before you start piping.
• Member Posts: 8
ok

I will get another opinion.  I have a call to another plumber who reportedly is a radiant expert.
• Member Posts: 8
Heating Loss

Real Quick.

BTW WE know boiler is oversized, but we may add a second floor in the near term. Boiler was installed last year.

My Plumber just told me the heating loss is 24,600 BTU/Hr.  The room is about 265 square feet.  He said we need tubing to be 8" on center and that we need over 400 feet and should do it in two loops.

Do we really need 400 feet to create that many BTU? The room is roughly 15 x 18.
• Member Posts: 891
No way, no how

100 BTU/sqft???

I don't care how many loops you have, to get 100 BTU/sqft into a 68 F room you'd need your floors to be 118 F, which is 33 F over the recommended max. You could almost use your floor as a food warming shelf!
• Member Posts: 891
And as to the boiler...

My house is a 1900 sqft two-story 1950s masonry construction with zip for insulation in the walls, no insulation between the first floor and the unheated basement, incomplete insulation in the ceiling, and drafty doors. Windows are bottom-of-the-barrel vinyl double-glazed, and they're plentiful. Last week during the sustained low-teens to low-twenties weather I was burning 33000 BTU/hr. This morning the outdoor temperature was 37 and I was burning 17000 BTU/hr. I keep the house at 68.

The boiler I replaced is a 1991 Burnham 169000 BTU/hr beast. I replaced it with a Triangle Tube PS-60. Projected reduction in propane usage is upwards of 60%. Food for thought.
• Member Posts: 3,085
Mixing Valve

The other issue may be the size or CV rating of the mixing valve. Is that properly sized for the needed flow? You may find you need to also increase the size of the mixing valve as well as the piping.
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
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