Hydronic Heating – Do I need a relay?
Flatfive
| Posted in Energy, Heating & Insulation on
I am installing a hydronic heating system in the back part of my house. I have 3 baseboard heaters that are 1/2″ copper pipes with fins on them. Two of them are 4 foot long and one is six feet long. They are connected through a manifold system to a Takagi tankless heater and a Taco 1/8 HP pump. Now, whenever the pump comes on the heater comes on and the heaters get warm. I have some wires in the walls for a thermostat (2 #18 wires). How do I get the thermostat to control the 110V pump? I guess a relay would work. I’d need a power source for the relay. There must be a standard way of handling this.
Replies
http://www.heatinghelp.com
Check out the books section. There should be one on controls etc.
Have you checked whether the wires have power at present? Seems to me all you'd need to do is get a 12v transformer and a DPST relay... If you need help with the wiring, drop me an email.
Paul
You stated that you had a TACO pump, contact them they make a pump controller. I am assuming that there are not 2 different companies with that name in the HH business
Yeah, you need a relay. The thermostat wires are not rated for 120V, nor for the current the pump draws.
It's a simple transformer/thermostat/relay setup:
(SPST/NO) relay contacts <---.-------------- 120V o---------- ------- AC --------- /----------------------------------- | | 120V / / | | AC / | | ---------/ -----------------X-----------------/ {O} 24V thermostat 24V pump transformer contact relay motor coilThe main thing to be careful of is that the relay is rated for the motor current, including startup surge. A purpose-made relay would be best, but general-purpose relays would work.
Remember that the 120V relay connections must be in an enclosure, and that the 24V connections SHOULD NOT be in the same enclosure. Same thing's true for the transformer. (I'm assuming a 120V pump here. It could be 240V.)
The transformer and pump need not be on the same 120V circuit, but it is less "surprising" to later service folks if they are. Note that if you have a 240V motor you should get a double pole relay (DPST) so you can switch both legs of the 240V line.
This is for a standard heating thermostat that closes its contacts when calling for heat. The setup can also be done with a "cooling" thermostat, but you need a different relay.
Note that "SPST/NO" means "single-pole, single-throw, normally open". Many general-purpose relays you find will be DPST or DPDT, but that just means that you have relay contacts you don't use.
Great! Thanks.
I got a TACO relay on ebay for $20. Works fine. Also, a Hunter programmable thermostat for $30. Now, I have heat!