Adding a radiant zone - do i need a control unit/relay or 110V thermostat?

drosner

Hi - I've got 6 existing zones with circulators to each zone controlled by a TACO 6 zone control unit. I'm converting a room from baseboard to radiant and will be putting the radiant on its own new (7th) zone. My plumbing contractor is planning to add a circulator that will be controlled directly from the thermostat by using a 110V compatible TS and running the neutral wire to/from the TS.

From what I understand about basic electricity this seems kosher to me - the TS closes when heat is called for which closes the circuit and therefore the circulator powers on and sends hot water to the radiant circuit. I assume TS with low voltage lines are preferred since its a lot easier to do the install - I guess.

Problem is - I asked him about the big circulator pump that is on the return side of my boiler....."doesn't that need to come on when heat is called for in any of the zones...". He said it was controlled by the boiler only and to prove it he showed me that none of the wires from the TACO 6 zone control unit went to that circulator or the boiler. Basically he said they were independent.

So 2 questions I guess..

1 - Is there a downside to the control approach of using a romex line to a 110V TS in order to directly control the circulator pump vs. getting a TACO SR501 or similar control/relay?

2 - What the heck does the circulator on the return side of my boiler do - and do I need to make sure that it comes on when this new zone circulator comes on for my radiant circuit?

Attached is a schematic of my system...i'm now kinda annoyed that i'm not "pumping away" as I've read in all of Holohan books! But I don't seem to have any air issues that I can tell...

GW

It may be good to snap a pic or two of your systems piping around the boiler. Your drawing makes no sense

drosner

Here is a picture of the piping around the boiler...

Hmm...I know i'm not using standard notation for plumbing schematics but it seems pretty straightforward. The supply side of the boiler goes to a bank of circulator pumps that feed each of the zones. They all come back to the return side and there is a larger circulator pump at the boiler on this return side. The DHW comes off a T connection at the supply side and then on the return side of the boiler - it has its own circulator near the tank.

So if I didn't know any better I would say this is a simple setup of a single primary loop that has 6 heat zones and 1 DHW zone. Each zone has its own circulator pump that is controlled by the TS in the zone. Because I want to add a 7th zone I need to understand what the larger circulator is on the return line near the boiler and if I need to make sure that comes on when the 7th zone circulator comes on.

Appreciate the help - I don't trust this plumber's knowledge with hydronics and this should be a simple job but I'd prefer to double check his design....

unclejohn

You will be much happier with a 24v tstat and relay.

drosner

Yea - instinctively I think I know that. But i don't know why that is better so I can push my contractor to "do it the right way". The plumber is a sub to my GC so I'm working within the fixed budget we set. So if I can justify this then it shouldn't cost me a change order...plus I'm trying to understand good hydronic design..

Dave H_2

To add the radiant zone, you are going to need a mixing valve also as well as a new circulator in order to control and lower the water temp needed for the radiant floor. The rest of your house has high temperature baseboard and radiant typically needs a lower temp.
I would use a low voltage thermostat and one more designed for radiant with small differentials and maybe a floor sensor depending upon design, finished floor covering and what room of the house this is in.
So using another relay to interface between the low voltage thermostat and high voltage circulator would be the best and probably the easiest.

Dave H.

drosner

Very helpful thanks!

I went back down and looked at my setup again. I actual do have a connection between the return and supply sides that is very close together. I also see that my 6 zone taco controller has a low voltage line to the boiler.

So to add a 7th circulator like a taco sr501 - can I connect that to the 6 zone controller or do I have to connect it directly to the boiler? I figure it would be easier to extend the 6 zone controller than the boiler.

Any suggestion on mixing valve? This will be pex in a concrete bed over a subfloor on a second floor bath. About 100 sq ft.

Also - does it matter which return I used to mix with the supply going to the radiant circuit?

Mark Eatherton

If your hand drawing is correct, the boiler is improperly installed. It has to be set up primary/secondary. And yes, you must provide cool water to the mixing valve FROM the radiant zone, otherwise the valve will lock up due to too high a return water temperature.

Also, the mixing valve should be down stream of the circulator serving that zone. The circulator shouldn't be guessed at. It has to be sized to the required flow and associated pressure drop.

As for line voltage thermostats, they don't come with any bells and whistles like the low voltage stats do. The actual "reason" that low voltage thermostats are used is because it doesn't require an electrical license (in most places/cases) to install wiring serving less than 50 volts. Running a line voltage stat indicates to me that the contractor doesn't understand how to do low voltage wiring, or how it is interfaced. Instead of setting a SR501, why not use a pump with a built in transformer/relay switch. It will make interfacing the controls to the boiler a LOT easier.

Also, its not indicated on your drawing, but every one of those pumps MUST have a check valve on its outlet. Once the boiler is repiped primary secondary, the boiler pump is a necessity. As it is now, on each call for heat you have two pumps in series, which is probably the only saving grace for the boiler, but is probably exposing your piping distribution system to a great potential for hydraulic erosion corrosion.

Refer to the manufacturers I&O manual for correct drawings. It will probably cost more to do it right, but it is the right thing to do.

ME

hot_rod

That boiler should really be connected to a primary secondary piping or a hydraulic separator. The boiler should have a dedicated pump sized to the manufacturers spec.

The is no way to assure a zone pump could supply adequate flow to the boiler and distribution.

As shown the boiler pump is in series with any of the zone pumps when both are running.

IF you decide to repipe adding a buffer tank could help the boiler cycle less. It would also serve as the hydraulic separator and allow you to easily pull a mixed temperature zone off.

drosner

Hi All - Really appreciate the comments and support on this.

I actually did get the hand picture incorrect - there are T connections between the supply and return sides near the boiler and they are closely spaced ( looks like 4"). This appears to be exactly the setup that the Munchkin manual specifies.

Does this still concern anyone if I add a 7th zone circulator?

drosner

with new picture...

Mark Eatherton

Good. Just make certain that pump is properly sized, has a check valve on its discharge, pumping away from the MIX port of the valve, with the radiant return as the cool source for the valve. Also make sure the other pumps have checks (IFC indicated Internal Flow Check) and you should be good to go.

ME

drosner

Yea - I see TACO 00 pumps can come with IFC built-in so I can get that for my new zone. My existing zones definitely don't have a flow control valve and when zones aren't running I can feel the heat on the supply line in some cases...

Mark Eatherton

I'd suggest that while you have it drained, have your contractor put check valves downstream of the pumps. Water is like my ex Brother in law. Wet lazy and stupid You MUST show the water what direction you want it to flow (checks) or it will follow the path of least resistance, which is probably not the path you want or need.

ME

MikeG

Mark,
I know you said the circ needs to pump away from the mixed port on the mixing valve, but he still shows the second drawing as pumping into the mixing valve correct?

Mark Eatherton

MikeG said:

Mark,
I know you said the circ needs to pump away from the mixed port on the mixing valve, but he still shows the second drawing as pumping into the mixing valve correct?

Correct Mike, hence my suggestion. Hopefully he caught that. I'd generate a drawing but have no spare time at present. Trying to get to Florida could be tricky...

ME

drosner

I got that detail - mix valve before the circ out to the zone.

I have an existing radiant zone that has the mix after the circulator. Been that way for years I imagine. How bad is that?

drosner

Hi - so my plumbing contractor is saying he must use a 110v tstat because "there is simply no space left to power it off the boiler with low voltage which is why we will run a 110v tstat"

I've got a taco sr506 6 zone controller and this would be the 7th zone. I told the contractor to get a taco 007 priority zoning circulator with ifc which has its own relay and transformer on it. I could be wrong but I thought when the zone calls for heat the zone circulator needs to come on AND I need to run a low voltage line to the boiler which has the control for the boiler primary circulator - right? If any zone calls for heat the circulator on the primary circuit for the boiler needs to run at the same time? The boiler fires if the water temp tells it to regardless of if a zone is running or not.

I've studied the muchkin manual but it's not clear to me the wireing. But this should be easy and I shouldn't need a line voltage tstat.

Am I missing something or is this guy clueless?

jokamo

Hi drosner, 

I am now having the same problem you had back in 2016 and I just stumbled upon your post.

What was the end solution to wiring low voltage to the boiler? 

Is it nessecary, or do I just need to connect the pump, 110/120v, and thermostat wires to the relay? 

Thanks I'm advance!

Joseph.

Big Ed_4

With radiant you want to use a thermostat with a floor sensor which would be 24v . The floor temperature needs to be controlled not the room air temperature for comfort. A separate length of Pex would be run down into the floor and into the wall behind the thermostat if the sensor needs to be replaced .. The new 501 and be interfaced to the 506 ...

WillC

Do all of you guys have a floor sensor thermostats at home? I was told to use an air sensor for a house. And that floor sensors were needed for hangers with heated concrete slabs, so when you open the doors multiple times a day, the thermostat doesn't call for heat every time.

Zman

@jokamo
There is rarely an identical situation when it comes to retrofitting controls.
It would be best to start a new thread with pictures and details of what you are trying to control.