Wire size for radiant floor boiler help

[nhraracer90]

Hello! I need some help in determining wire size for my radiant heat boiler to run in the wall before I close the wall up (drywall).

Boiler panel will be about 35-40 ft max from breaker box on the same wall. I already have the 120v wire ran (10/2) for the thermostat, some sensors, pump and relays. The company I got a quote from for the boiler panels told me I’ll need a 60amp 240v breaker for the boiler part. I know the quoted boiler is 39,000 btu, 11.5kw @ 240v/1. I am not going to be doing any of the wiring hookups, I just want to get the wire ran in the wall before I do my drywall work. Would a 6/2 wire be big enough?

Any help would be appreciated

Thanks!

 

[mm08822]

NM-B 6 gauge copper will work. Verify (before you buy) that the boiler only needs 240vac vs. 120/240vac. I.E. 6-2 vs. 6-3.

The thermostat doesn't require low voltage cabling? 10/2 is a rather odd requirement for boiler control and then you mention 120v. I suggest you get the install out and post what it requires for electrical connections.

Are there any sensors, pumps, relays remote from the boiler?

 

[nhraracer90]

NM-B 6 gauge copper will work. Verify (before you buy) that the boiler only needs 240vac vs. 120/240vac. I.E. 6-2 vs. 6-3.

The thermostat doesn't require low voltage cabling? 10/2 is a rather odd requirement for boiler control and then you mention 120v. I suggest you get the install out and post what it requires for electrical connections.

Are there any sensors, pumps, relays remote from the boiler?

Okay I will check with the 6/2 vs 6/3 wire but I could always run 6/3 just in case right and not use the extra wire? They told be I’d need a 120v circuit for the sensors, pumps and relays separate from the boiler circuit and I had some extra 10/2 laying around. I know the 10/2 is probably overkill for that part of it

 

[mm08822]

You could run 6/3. If not needed, it's then dead money in the wall.

 

[wyliesdiesels]

Hello! I need some help in determining wire size for my radiant heat boiler to run in the wall before I close the wall up (drywall).

Boiler panel will be about 35-40 ft max from breaker box on the same wall. I already have the 120v wire ran (10/2) for the thermostat,

10 gauge wire for a thermostat? thats awfully large for a thermostat. are you sure its 120v? I dont think ive ever seen a 120v thermostat. theyre usually 16-24v and get power from the control panel. you only need 18awg max....

some sensors, pump and relays. The company I got a quote from for the boiler panels told me I’ll need a 60amp 240v breaker for the boiler part. I know the quoted boiler is 39,000 btu, 11.5kw @ 240v/1. I am not going to be doing any of the wiring hookups, I just want to get the wire ran in the wall before I do my drywall work. Would a 6/2 wire be big enough?

Any help would be appreciated

Thanks!

11.5kw is ~48a x 1.25 (continuous load factor) = ~60a rated wire.

youll need at least #6 regardless of what type of wire you use (NM-b or THWN in conduit)

 

[T444e]

Line voltage thermostats are uncommon in residential, but are readily available and are common to see in older industrial applications and are still used in some new installations. I don't have any experience with electric boilers, but I wouldn't think they would run the full current through the thermostat, would have to see a wiring diagram.

 

[Bert_]

Technically #6 romex is 55A but I know what most would do.

#10 physically will not fit in those pumps and control panels. #14 is normal.

I would expect a 24v thermostat. Would run #18 stat wire.

 

[dave*99]

Okay I will check with the 6/2 vs 6/3 wire but I could always run 6/3 just in case right and not use the extra wire? They told be I’d need a 120v circuit for the sensors, pumps and relays separate from the boiler circuit and I had some extra 10/2 laying around. I know the 10/2 is probably overkill for that part of it

Post the owners manual wiring diagram. I think there is another issue in play here. I suspect the boiler needs 6/2 to feed a contactor that runs the heating element.

You mention separate from the boiler circuit. It's possible a 120V 15A or 20A circuit is needed to feed a control system. Tapping a 60A heater feed for the 120V stuff only works if there is fusing/protection provided in the boiler control system. You don't want a small pump wired to a 60A circuit.

You mentioned 10/2 for the thermostat. Post manuals/info etc. I can't imagine a system that needs 240V @ 60A for the heating elements and then a 120V thermostat circuit.

Perhaps you have a control system operating on 120V and it has a transformer that feeds 24V to a thermostat. That thermostat run would be 18GA. Probably 18/2 from thermostat to control panel.

 

[sparky 1971]

^^^This^^^
The last boiler I wired had an integral pump. 60 amp 240 for the boiler, AND 15 or 20 amp 120 for the pump AND a 24 volt thermostat. Thus, it had a 6/2, 12/2, and 18/2 run to it. I believe it was called a boiler in a box or something like that.

 

[wyliesdiesels]

Technically #6 romex is 55A but I know what most would do.

#10 physically will not fit in those pumps and control panels. #14 is normal.

I would expect a 24v thermostat. Would run #18 stat wire.

55a is not a standard breaker size per 240.6(A) and since the load is less than 55a, its code permissive to put it on a 60a breaker

 

[Bert_]

55a is not a standard breaker size per 240.6(A) and since the load is less than 55a, its code permissive to put it on a 60a breaker

You can use a 60A breaker, for a load requiring 55A wire. This needs 59.9A wire.

 

[wyliesdiesels]

You can use a 60A breaker, for a load requiring 55A wire. This needs 59.9A wire.

the load is not 60a. the load is 48a

 

[Mr onetwo]

C'mon OP.....we need some basic info.Like manufacturer and boiler model number

 

[Mr onetwo]

This seems to be the most common boiler of this type on the interwebs https://www.acwholesalers.com/Elect...FHypKHnqhHQThbRqU0nHcPe0vdRz0f59FBw-tjeVXh4Pt

wiring is just like the op states

 

[nhraracer90]

I have attached the install manual for the boiler. I was quoted the model number B-12U FFB. It was a quote from BlueRidge Company and all he could tell me was that “I’ll need a 60a 240v breaker for the boiler and also 120v power to supply the pump relay that powers pumps and thermostats”.

I don’t know much about wiring and such so sorry for the vague description lol.

A 6/3 would also be able to provide the 120v wouldn’t it?


FYI I just originally ran the 10/2 myself before I actually knew the specifics of what’d I’d be installing. So it may not even be needed for anything

 

[Bert_]

the load is not 60a. the load is 48a

Article 424 includes electric boilers and 424.3(b) states they are considered a continuous load.

210.19(A)(1) says the conductors need to have an ampacity of 125% of the continuous load.

I don't see a way around that?

 

[PCustoms]

I have attached the install manual for the boiler. I was quoted the model number B-12U FFB. It was a quote from BlueRidge Company and all he could tell me was that “I’ll need a 60a 240v breaker for the boiler and also 120v power to supply the pump relay that powers pumps and thermostats”.

I don’t know much about wiring and such so sorry for the vague description lol.

A 6/3 would also be able to provide the 120v wouldn’t it?


FYI I just originally ran the 10/2 myself before I actually knew the specifics of what’d I’d be installing. So it may not even be needed for anything

Any particular reason you settled on electric and not gas?

 

[sparky 1971]

“I’ll need a 60a 240v breaker for the boiler and also 120v power to supply the pump relay that powers pumps and thermostats”.

You need both 240 and 120

A 6/3 would also be able to provide the 120v wouldn’t it?

Yes, but not in this case

FYI I just originally ran the 10/2 myself before I actually knew the specifics of what’d I’d be installing. So it may not even be needed for anything

Leave the 10/2 for the 120, it's way more than you need but since it's already been installed, what else are you going to do with it. The boiler guy that connects it will be cussing you a little bit when making the connections, but he'll get over it eventually. You also need to run a 6/2 for the 240. And a 18/2 stat/bell wire for the thermostat unless that is part of the installers scope of work. Officially, the 6/2 is a bit undersized, but I wouldn't lose any sleep over four amps.

 

[nhraracer90]

Any particular reason you settled on electric and not gas?

Not really. I would need to get gas which I don’t have installed here so electric is easier

 

[nhraracer90]

You need both 240 and 120

Yes, but not in this case

Leave the 10/2 for the 120, it's way more than you need but since it's already been installed, what else are you going to do with it. The boiler guy that connects it will be cussing you a little bit when making the connections, but he'll get over it eventually. You also need to run a 6/2 for the 240. And a 18/2 stat/bell wire for the thermostat unless that is part of the installers scope of work. Officially, the 6/2 is a bit undersized, but I wouldn't lose any sleep over four amps.

Okay I figured the 10/2 is overkill but oh well lol. So I’ll run some 6/2 over and call it good then. The 18/2 for the stat would only need to go from where the boiler is to wherever I mount the thermostat right?

 

[sparky 1971]

Okay I figured the 10/2 is overkill but oh well lol. So I’ll run some 6/2 over and call it good then. The 18/2 for the stat would only need to go from where the boiler is to wherever I mount the thermostat right?

Yes

 

[nhraracer90]

Yes

Awesome thank you!

 

[brewchief]

Run an 18-3 or 18-4 for the stat, this way you can have a common wire if you want to add a smart or wifi stat in the future or even to keep the average battery powered digital stat from causing problems when the batteries die.

 

[nhraracer90]

Run an 18-3 or 18-4 for the stat, this way you can have a common wire if you want to add a smart or wifi stat in the future or even to keep the average battery powered digital stat from causing problems when the batteries die.

Okay gotcha. Thank you!