control blower with thermostat

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Old 09-04-08, 06:15 PM
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control blower with thermostat

I'm finishing up installing an outdoor wood boiler. I have an old NewMac wood/oil combination furnace in the basement and am using the blower from it to heat the house. I have a heat exchanger installed in the plenum and need to figure out how to turn on the blower when the house calls for heat. The hot water from the boiler will be constantly circulating through the heat exchanger.



The picture shows the control board (not sure what its called) where the thermostat wires come in, it is right behind where the blower is. The top portion usually has a cover over, I just removed it to see whats behind it.

-Thermostat wires come in:
- Black to W
- White to R
- Red goes to a connector at the top, then goes to the black box on the right, then connects to the G terminal as a blue wire

-Burner wires connect:
- Red to R
- Yellow to W

-Two yellow wires connect to the T terminals and go into the electric box behind the connectors

Any help would be greatly appreciated. I probably could use a line voltage thermostat and bypass all this, but I would like to use my current thermostat. I plan to just disconnect the red and yellow wire to the burner. That should stop it from trying to fire, right?

Thanks
Rob
 
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Old 09-04-08, 07:29 PM
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Fan control via t-stat

Are there any numbers on or inside the cover? What you want to do could be easily done via a switching relay such as a Honeywell RA89A. You would simply bring 120 into the relay which contains a transformer, send 24 VAC out to the stat connected to R & W, & connect the blower to the load terminal of the relay. By doing this, when circuit R/W closes & creates a call for heat, the fan will come on. When R/W opens (room is up to temp) the fan shuts off. You could provide further control by using a strap-on aquastat on the pipe returning to the boiler thus shutting down the fan should the water temp drop below X (130 for example). The aquastat could be wired in series with the relay via 'W' or in series with the fan motor.
 
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Old 09-05-08, 05:05 AM
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I found some numbers on the silver box just above the wire connectors it is Honeywell R8405C1007. And the black box to the right has a paper label that's just about worn off but it starts R8225....

While googleing I found http://www.hvacmechanic.com/forums/r...ages/29066.htm and it looks similar (although his number is B1009 at the end), they called it a "fan center".
 
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Old 09-05-08, 05:19 PM
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R8405

I couldn't find anything on Honeywell's site about the R8405 & without knowing just what that relay does & how it is wired, it's difficult to advise you on how to do what you want. The R8225 with the addition of a transformer would serve in place of the RA89A.
 
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Old 09-05-08, 06:32 PM
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I have a 24 volt transformer that I just purchased for the upstairs baseboard heat. Could I put a second set of wires on that?

The R8225 has two wires on the outside; a dark blue that connects to the red wire of my thermostat and a light blue that connects to the "G" screw on the board. And two black wires in the electrical box, one goes to one wire from the fan and the other to the fan and limit control. All wires are 12 or 14 gauge wiring not 18 thermostat wiring. I updated the picture above to show where the wiring on the outside of the R8225 goes.

http://s143.photobucket.com/albums/r...=dcp_1561A.jpg

Does this help at all or should I just break down and buy and RA89A?
 
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Old 09-05-08, 06:53 PM
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Existing controls

I'm reasonably sure the existing controls would work. It's just a matter of disconnecting wires which are not needed & connecting wires to power the stat & operate the relay which in turn would turn on the fan. I'd almost be willing to bet if you set the thermostat fan switch to "ON", the fan would run. The problem is, it would run all the time.

Another concern is with hot water circulating thru the duct coil all the time you are going to get heat even when you don't want it simply by natural convection. In applications like your's a 3-way zone valve is often installed. The normally open side of the valve is piped with a coil by-pass & the normally closed side is toward the coil. When the stat calls for heat the valve switches & allows hot water thru the coil to heat your house.
 
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Old 09-05-08, 07:19 PM
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I think we can make it work with out the need of relays and what not..

What do you have now for t-stat? (make and model#)

In my mind, I am thinking if you have a newer t-stat that can be program as Heat Pump Mode, the stat will turn on the fan in heat mode..

I've never been around these wood boilers, so I am thinking, a lot of hot water is not being used is wasted when you don't need the heat... Is there something you can do to send the heat to a holding tank for hot water in the house?
 
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Old 09-05-08, 08:21 PM
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What I have now is a ritetemp 8022c thermostat, I have three wires coming from the furnace, black to W, white to Rh (which has a jumper to Rc, I do not have AC) and the red wire is not hooked up to the thermostat but goes through the R8225 box on the furnace and connects to G. (I replaced the old round thermostat and that wire wasn't hooked to anything so I left it off).

I was reading another forum and they said to hook the wire that goes to G (my red wire) to Rh and that will cause the blower to kick on when the house calls for heat. Sound good?

They way outdoor wood boilers work is they keep the water at 180deg (or you can change it a little), they automatically control how the fire burns to keep that temp by a draft fan. It then runs trough a heat exchanger to heat my hot water, then through the heat exchanger in my plenum, then I have a three way zone valve for baseboard in my upstairs I just installed, then back to the boiler. It is constantly circulating the hot water.
 
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Old 09-05-08, 08:51 PM
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Ok, That stat won't work the way I am plan on helping you.

The stat I suggest is the Honeywell RTH7400 model. That stat can be used with heat pump, but since you don't have A/C, that not a problem, and will make my plan work very well.

This is my plan.

to program the stat as heat pump with back up heat. (your oil)

So when the stat is in regular heat mode, the stat will power up Y and G (Y won't be used, but G will be used).

And when the house temp falls behind or wood has burnt up, the oil then will kick in.

If you are not using wood, and just only want to use the oil heat, then switch the stat from heat to EMG(ency) heat, and only the oil will come on.

So if you want to do that, you need to run to Home Depot and get the stat I mention above, and I'll help you wire/program it.
 
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Old 09-06-08, 04:05 AM
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I am no longer using the oil furnace, only the blower on it. It is a really old 1974ish oil/wood combination and needs a new oil burner to work properly. The outdoor wood boiler has a propane gun as backup heat (hopefully never to be used, but I got it just in case).

Does that change anything, can I use my current t-stat
 
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Old 09-06-08, 05:22 AM
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Ok, then yes, that changes things if you don't plan on using the oil burner.

The W wire then can be moved over to G on the control.. So when the stat calls for heat, it will power up the G at the control to run the fan.

I would strongly suggest to get the oil burner up and running that that big IF something happens to you, you got back up heat... and when you do need it, move the wire from G to W at the control
 
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Old 09-06-08, 12:42 PM
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The outdoor wood boiler has a propane backup burner on it, so if I don't fill it with wood that will kick on.

Well I tried switching the W wire to the G terminal and got nothing when I turned up the heat. I also switched the W wire with the wire that goes into the black box which then connects with the G terminal, and when I turn the heat up I hear a clunk through the duct work.

I can turn the blower on manually via the switch on the temp limiter on the plenum. So they seem to be fine.

Any other ideas
Thanks
Rob
 
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Old 09-06-08, 06:27 PM
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Temp Limiter?

That limiter may actually be a fan & limit switch not allowing the fan to come on until the control senses at least a certain temperature. A tip off as to it's funtion could be the number of wires connected. Two wires would likely indicate strictly a limit. Three or more would make me think it is a combination control. Any numbers on it? L4064-xxxx is a common Honeywell fan/limit control #.
 
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Old 09-06-08, 08:28 PM
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Thanks for the help, I'll have to get back to you in the mornin'. I took a quick look and there are three wires to the limiter, but there is some surface rust on the top. I'll see if I can find a model number somewhere in there. It is a Honeywell.
 
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Old 09-07-08, 05:19 AM
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Another Tip-Off

If the limiter has a button (usually white) which goes thru the cover & you can push to turn the fan on manually, the control is almost certainly a fan & limit combination.
 
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Old 09-07-08, 05:48 AM
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At this control, what happens if you jumper R to G?

Do you have a meter to see if you are having power at R?
 
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Old 09-07-08, 07:40 AM
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R to G produces a clunk sound.
R to W I have 26 volts

The limiter does have a button to switch between automatic and manual. I could not find a part number on it. It does have three wires, blue to Fan-Load, red to Limit-Load, black to Limit-Line.

Thanks for all the help guys
 
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Old 09-07-08, 11:19 AM
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Sounds like the fan center is working like it should, you may be losing power to the relay from the fan center.
 
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Old 09-07-08, 07:33 PM
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Voltages

When you jump R to G, check for 120 volts between blue (fan load) & ground. I suspect you will not get 120. Normally if the fan is inteded to run with the thermostat set to "fan on" (same effect as jumping R-G) there will be four wires connected to the fan/limit. The fourth would be connected to "fan-line" & the brass jumper between "limit-line" & "fan-line" would be cut. It would seem your's is wired as in Figure
9B here:
http://customer.honeywell.com/techli...0s/69-0117.pdf
 
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Old 09-08-08, 11:01 AM
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Between
Blue and ground I get 0
Black and ground 120
Red and ground 120
Black and Blue 120

I tried running a jumper between Blue and Black, thinking I could bypass the switch, but that just turned the fan on constantly, even when the house wasn't calling for heat.

Figure 9B looks right, although I'm not sure were all the wires go.
 
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Old 09-08-08, 03:06 PM
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Originally Posted by Grady View Post
What you want to do could be easily done via a switching relay such as a Honeywell RA89A. You would simply bring 120 into the relay which contains a transformer, send 24 VAC out to the stat connected to R & W, & connect the blower to the load terminal of the relay. By doing this, when circuit R/W closes & creates a call for heat, the fan will come on. When R/W opens (room is up to temp) the fan shuts off.
I'm wondering if this is the better way to go, and be done with it. This is what I want, right? HONEYWELL-RA89A-1074-SWITCHING-RELAY
I've also seen Honeywell has fan centers, is there any difference? Fan Center

Thanks for all the help.
Rob
 
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Old 09-08-08, 05:29 PM
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Relay or Fan Center

As I see it, maybe right maybe not, the problem would appear to be wiring. I think the existing control would do the job IF functioning & properly wired.
Presuming you have no intention of using the oil burner & don't care if it is disconnected & all you want to do is control the fan via the thermostat it is quite easy. For a novice, the
RA89A would be easier to wire & that price (so far) is quite good.

1. Disconnect incoming power to the furnace.
2. Disconnect all furnace wiring.
3. Connect incoming power to terminal #1.
4. Connect incoming & load neutrals to terminal #2.
5. Connect load (fan motor) to terminal #4.
6. Connect terminals T&T to R&W on t-stat.
7. Re-apply power.

On a call for heat (R/W closes), the fan will be energized. When the room is up to temperature (R/W opens) the fan will shut down. My concerns about unwanted heat or lack of warm air with this type of control scheme stand but if you want simple, this will work.
 
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Old 09-16-08, 03:07 PM
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Just wanted you guys to know, I installed an RA89A switching relay and it works perfectly. Thanks for all the help.

Rob
 
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Old 09-16-08, 07:36 PM
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Glad to hear you are up and running..

Did you wire up the W to G on the relay?
 
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Old 09-17-08, 08:21 PM
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Thumbs up Good Job

Hope it works well for you. Glad we could help.
 
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