aquastat, circulator, step down transformer, and relay electrical question

[MaryM]

I have an in the basement wood boiler. I put in a 110 v aquastat connected to a circulator 110v. When the temp rises to 140
the aquastat kicks the circulator on and pumps upstatirs to some radiators. Everything works good. There is also a gas hot air furnace in the house that has a hot water coil in the plenum that i recently connected to the wood boiler. the coil heats up good when the circulator kicks on. what I would like to do is trip the fan on the furnace on when the circulator comes on to take advantage of that 140 temp water circulating. My thinking is that if I connect a step down transformer powered by the circulator circuit (110v to 24v) and ran the 24v line over to the furnace fan(where the upstairs thermostat wire is connected), i cold trip the furnace fan on by the energized circulator circuit. Am I thinking about this correctly?

A fellow at a one of those big box stores suggested that I would need a relay to accomplish this but I didnt really understand what he was getting at. Ive been reading for endless hours in the "Boiler room" but I'm not understanding why I need a relay. Sorry for the "do it your selfer" questions, but i have the time now to do it and thought maybe i could save a couple of bucks. Thanks for all your help!

 

[stee6043]

The problem you may run into is if you use a "separate" power supply to switch on the fan you may fry the existing transnformer in your furnace. Do you have an A/C circuit on your furnace? If so, many folks find it very easy to use the A/C circuit to switch on the fan. Simply throw the breaker for the A/C to "off" and tie into the A/C control wires. Quite painless. The furnace thinks the A/C is on but the compressor does not run.

PS - Depending on outside temps you may find that 140 degree water is not hot enough to effectively heat your house with the heat exchanger in the furnace. For me 160+ is good. Anything less than 150 is not so good....

 

[MaryM]

Thanks Stee for your reply. I should have mentioned that I would like to keep the gas hot air furnace operating because when the fire goes out at night and the house cools down the gas hot air furnace kicks on to keep the house warm. I dont have any storage(for now). there is a fan on off switch on the existing furnace thermostat. I was thinking that somehow I could attach the 24 v wires from the transformer to the same location as the existing thermostat wires for the fan on/off circuit. this way the furnace could run overnight. Thanks!

 

[overshot]

Your existing thermostat will get 24v from batteries or the gas furnace transformer, so I dont hink you need the transformer. Use your "fan" wires with a relay. Relays are cheap on ebay.

 

[RJP Electric]

Why couldn't you put a strap on aquastat on the outlet of your plenum coil connected to the R and G of your fan center of your gas furnace. When the water hits 140 the fan will come on, you may also want to cut in a separate thermostat in the mix for a little control.

 

[mrk88mrk]

If I'm understanding your appliaction I don't think this will work in that way. A relay device does not step down voltage from 110 to 24V. The relay only serves as a switch. When a low voltage signal from the thermostat tells the switch to close it activates a magnetic field that closes the switch from the line voltage to the load (circ pump). I hope this helps.

 

[cguida]

I don't completely understand the problem, so I probably outht to keep my mouth shut (for a change). But why can't you have a 120v relay from the Boiler or circulator, and use it to toggle the 24 volt hot air furnace thermostat line? That way there would be no direct electrical connection between the two systems. It's alittle stange to be using 120volts as the signal line to power the realy, which in turn handles the 24v thermostat line.... usually it is exactly the opposite with the low voltage controling the high voltage.

But I have a similar problem between my wood boiler and circulators on the oil boiler side. I want the action of a 120v aquastat to control a thermostat line which in turn will do someting to a zone circulator. Sounds like a mess, and probably is -- this is what you get when you steal an oil boiler aquastat...

 

[overshot]

The cheapest solution is a 120v coil relay. You use the 120v from the circulator circuit to close the coil when the aquastat turns on the pump. On the other side of the relay - put your 24v circuit on a NO (Normally Open) contact. When the 120v coil closes it will close the 24v circuit. Run the 24v circuit to the fan wires. This will turn on the fan when the circulator turns on. If you hook this up to your t-stat circuit - you will turn on the gas part of the furnace as well as the fan part. I dont think you wan to do that.

If you want to spend a couple dollars more - put a t-stat in the 24v fan circuit (series) for more control like RPJ Electric stated.

Coil relays come in many configuration, 120v coils are common. They are just a mechanical way to flip a switch - they dont have to be the same voltage,currant or wave form on both sides and 90% of the time they are not. Industrial controls use AC coil relays to switch DC circuits all the time.

 

[MaryM]

Oh wow! thanks for all the great suggestions, I don't know where i would be without all the great help from this room. I spent the long weekend thinking it over and I think I have a better understanding of what I am doing.

I was thinking that one way to do it would be to have a relay coil triggering when the circulator activated from the aquastat.
the load side would be 120v from the circulator and the switched side would be 24 volts running over to inside the furnace where the fan thermostat wires are connected "R" and "g". I could connect them there and close the circuit to kick on the fan. However i was concerned that i would be energizing those lines up to the thermostat at the same time. I m not sure if that would cause a problem. Another concern is if the circulator came on and energized the 24v circuit and someone accidentally flipped the fan auto switch on the thermostat on, i would have two 24v energized lines from two different sources and I not sure what would happen but I dont want to take the chance. That said.....

I think that i would disconnect one of the fan terminal wires, (not sure which one yet, r or g) and then splice and run that wire over to a relay switch. Run a return line back over to the disconnected fan terminal. The 120 circ supplies the on/off to the switch. The switch then completes the circuit back to the fan and activates the fan. this would presume that the Fan Auto switch stayed on (although never completed) and when the circ came on, the relay switch would complete the circuit and turn on the fan. this way i don't have to worry about short circuiting my control board in the furnace. I would never get to use the "fan auto" but then i never use it anyway. And i am assuming that the relay switch is a "switch only" triggering the completion(close) of the 24v circuit but not supplying power to it. Also forgive if my terminology is a little confusing, i was a little confused about the switch "opening or closing" the circuit. I like to think of it as completing the circuit.

I looked into a relay today but most switch from the 24v side(naturally from the thermostat side). But i need the switching trigger to be the 120 v side. Do i have this right? I couldn't find one but I ll keep looking.

What am I missing? Am I thinking logical? Am I in over my head? My 16 year old son told me "Mom, you're in the deep end of the pool." thanks junior...just what I need.

Anyway...thanks again everyone for your help. Its very much appreciated!

 

[RJP Electric]

If you buy a relay like this (broken link removed to http://www.functionaldevices.com/pdf/RIBU1C.pdf) they are cheap on ebay.
Connect the 120 volt portion of the relay to the circulator power and the blue N/C and common yellow of the relay to the R and G terminal on the furnace. There is not two 24 volt power sources that you mentioned, also there is no need to disconnect the wires existing on the furnace either.

 

[overshot]

If you buy a relay like this (broken link removed to http://www.functionaldevices.com/pdf/RIBU1C.pdf) they are cheap on ebay.
Connect the 120 volt portion of the relay to the circulator power and the blue N/C and common yellow of the relay to the R and G terminal on the furnace. There is not two 24 volt power sources that you mentioned, also there is no need to disconnect the wires existing on the furnace either.

Or try Automation Direct (online)#QM2N1-A120 $4.25 Relay, #SQMO8D $3.25 Socket

 

[Chris S]

We have installed several system such as you describe, installing an aquastat ( in a well, but strap on will work, also) on the return piping from the blower, usually set at 160, so as not to blow cold air. The aquastat is a switch, and doesn't care what the voltage is. It can then be wired parallel to the blower wiring to turn on the blower only when heat is sensed, and shut it off as temperature drops. One problem you may want to look out for, is if your piping/ flow is inadequate for your coil, it is going to switch on and off as it heats and cools, just a heads up.

As mentioned above however you should have a t stat so that you don't overheat. This is liable to be a big btu draw on your system, and you;ll want to contro; it.

As to what Smee said , a relay, such as a honeywell 8845U will probably do what you want, it has auxillary contacts, and can be used to take the place of sevaral other relays.

Chris

 

[MaryM]

thanks everyone with their well thought out responses. they were all very helpful.
Well, i decided to go the relay route, it was considerably cheaper than the strap on aquastat.
The RIBUIC arrived today. not much literature though with it, actually just the box. This is how i was going to wire it:
on the 120vac side ......the line coming from the aquastat to the circulator, i can just splice off of that line to the relay(Wht/Blk). and the other line from the relay(Wht/Yel) goes back to white neutral.
Hopefully, I have that right. thanks again everyone

 

[MaryM]

well i have the RIBU1C hooked up but the problem is when the aquastat is not activated the fan runs. when the
aquastat is activated the fan turns off. i reversed the lines on the fan side but same result. I have a feeling that the
orange (ORG) line needs to be connected to the fan terminal rather than the yellow line. back down to the basement.....

 

[overshot]

Relays come with NO (normally open) and NC (normally closed) contacts. It sounds like you have the fan hooked up to NC - this keeps the fan on when the circulator is off and when the circulator is on the fan turns off. Change your wires on the relay to NO and it should work.

 

[MaryM]

as Kramer says "OOOOOO MOMMMA!"

sometimes it just the small insignificant things in life......

 

[MaryM]

exactly overshot, it works, thanks

and thanks RJP works great!