Wood furnace with oil furnace

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Old 02-02-14, 10:31 AM
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Wood furnace with oil furnace

We have a two hot water furnace system here - an oil fired boiler and a 'supplemental' wood fired boiler. The wood fired boiler has essentially no controls other than an aquastat that controls a damper to shut of air to the fire - but I've never seen it get hot enough to cause that to happen.

Until this season, we'd never used the wood fired furnace at all, but due to the oil furnace not working (water in the oil tank), I decided to fire the wood furnace up, and found it worked OK (not enough BTU to get super hot, but took the edge off). All that was needed was to open 2 valves and close 1 to allow the circulating pump to circulate through the wood furnace. While the oil furnace was not working, this worked fine - the stack safety had locked out the oil burner, but left the oil furnace controls energized, so the circulating pump operated and hot water was pumped around the house (and through the oil furnace - whose controls made the system work).

Now I've gotten the water out of the oil tank, and the oil furnace is working normally, things do not work the way I'd like. I would like to fire up the oil furnace for an hour or so to get the system initially hot, and then rely on the wood furnace to maintain temp as best it can. However, in order for the circulating pump to run, the thermostats must be calling for heat, which causes the oil burner to run.

However, there is no way to turn off the oil burner when I want, without disabling the controls that allow the circulating pump to run.

Is there any way to do this?
 
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Old 02-02-14, 10:56 AM
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hi mshedden Ė

Iím NOT one of the experts, just a newbie. But on your other thread I think you said you also have a Heat Pump. Wouldnít a proper solution be the integration of all 3: the boiler, the wood burner, and the Heat Pump? Just throwing that out since it may or may not be significant to the experts. Canít hurt! LOL
 
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Old 02-02-14, 11:48 AM
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Possibly. It is possible to use electronic thermostats and a relay to control both the heat pump and the oil boiler and switch between them based on outside temp. The wood furnace is a separate issue though.

In this case, a simple switch on the power going to the oil burner may be what I need...
 
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Old 02-02-14, 11:51 AM
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What burner is installed on the oil boiler?
 
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Old 02-02-14, 12:42 PM
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The burner is made by Beckett
 
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Old 02-02-14, 01:08 PM
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I would suggest to pipe the wood boiler in parallel to the oil system, or you may cause condensation. Search "system 2000 wood stove" in the search bar and read thru that thread.
 
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Old 02-02-14, 01:49 PM
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The burner is made by Beckett
On the burner, there is a control box mounted above the motor.

There are two terminals on that box labeled " T T " and may have a jumper wire between them.

There MAY be wires connected to them, but probably not. If there are, stop and let us know where those wires go before continuing.

If there is a jumper wire, you can remove it and then wire a simple switch between them. When they are open, the burner will not attempt to fire.

Those terminals are LOW VOLTAGE, 24VAC and you can use regular thermostat wire to the switch.
 
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Old 02-02-14, 02:04 PM
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UPDATE to previous thread...

I just saw your other thread and you do NOT have the control on your burner that I thought you did.

In this case you don't have much choice but to do something with the 120VAC wiring.

You could install a junction box on the side of the boiler and run that AC cable from the control to the burner through that junction box and install a switch there. Your stack switch will lock out on a call for heat, but so what?
 
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Old 02-02-14, 02:20 PM
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I think mine must be considerably older or less complicated than most - nothing in the way of a control box. Above the motor is the transformer for the spark, With the transformer flipped up, I can see where the power wire comes into the Beckett, and runs to the motor and the transformer (just wire nuts in there). The power wire to the Beckett comes from a junction box a few feet away that is fed from a big dual pole 30A switch (looks like that feeds power to everything on the boiler). A switch on the incoming power by the beckett (or below the junction box) would do the job I should think.

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Old 02-02-14, 02:24 PM
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OK! Yes, probably below or beside the junction box that is partially hidden by a safety valve in that pic.
 
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Old 02-02-14, 02:27 PM
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Yes, I didn't realize your system was that old... most oil systems these days do not use the 'stack switch'. That control has been integrated into what is known as an 'oil primary control'. The stack switch has been largely replaced with a 'CAD CELL' that is inside the oil burner tube and 'sees' the flame.

Your system requires that the burner fires, and within the lockout time of the stack switch, the hot flue gases heat up a bi-metal strip and keep the burner from locking out. If the strip doesn't heat in the specified time (45 seconds?) it locks out.

CAD Cell actually 'sees' the flame. If it doesn't see flame within the lockout time, same same... locks out burner.

CAD cell is MUCH more reliable! No moving parts...
 
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Old 02-02-14, 02:31 PM
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If having to reset the stack switch seems a bother when switching from wood to oil, you could insert the switch into the wire that comes from the " B1 " terminal in the 8124 aquastat.

It appears everything goes into that 4" j-box below your service disconnect (boy, talk about overkill! )

If you insert the switch into that B1 wire BEFORE it heads off to the stack switch, it won't trip because it will never see call for heat from the aquastat.

Circs will still operate normally... what you want.
 
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Old 02-02-14, 02:43 PM
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Thanks for the explanation - this setup dates from 1952, no doubt some mods done over the years adding to the wiring sprawl. Stack switch seems to work fine (yes, about 45 secs), and if it ain't broke...

I'll take a look at what you've suggested re: B1 wire, although resetting the stack switch isn't *that* big of a hassle, but not having to would be neater.
 
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Old 02-02-14, 03:11 PM
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If you wanted to get REAL slick, you could mount an aquastat (something like an L6006) on your wood boiler and set it to something like 140 or so... wire the contacts of that aquastat to open/close the circuit to the burner. When woody gets hot, it automatically cuts off the burner.
 
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Old 02-02-14, 03:51 PM
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If the wood boiler circulates hot water through the oil boiler and the oil high limit is set lower than 180f the hot boiler water will keep oil burner off until wood is gone . If the units are piped and wired correctly it should work now.
 
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Old 02-02-14, 04:30 PM
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I don't think there's a pump between the two... which would be ideal...
 
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Old 02-02-14, 06:49 PM
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I'm sure something along those lines would be possible, but I think the hot water from the oil boiler circulating through the wood boiler would trigger the aquastat in the wood boiler without the wood boiler even being lit, making the oil boiler self extinguishing.
 
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Old 02-02-14, 07:30 PM
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If the wood boiler circulates hot water through the oil boiler and the oil high limit is set lower than 180f the hot boiler water will keep oil burner off until wood is gone . If the units are piped and wired correctly it should work now.
Probably I am looking for 'too much' control over when oil is burned!

Yes...it may be possible to adjust the oil boiler aquastat in such a way as to make that work, probably by having a large DIFF to keep the oil boiler off while the wood is burning, if enough heat is generated by the wood to keep the temp above the oil cut in temp (high - diff). The wood boiler does not generate as high a temperature as the oil boiler though, evn flat out.

Also, since the wood boiler cannot be 'shut off' as the oil boiler can, so long as it has wood in it, I prefer that the circulating pump be running constantly to wring whatever heat there is out of it, which mean the thermostats must be calling for heat all the time the wood is burning in order to keep the circulation pump on - I don't necessarily want to burn oil as the wood is burning down.

Lastly, without some kind of cut out on the oil burner, I can't run the wood boiler on its own, as the oil burner will fire if the thermostat calls for heat.

Probably more 'playing' is required...
 
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Old 02-02-14, 08:23 PM
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As loong as you run your t-stats through the aquastat the boiler will run. If oil is the last resort for heat then why don't you release the relay and wire your circulator to that independent source. Take it off c1 & c2 and run it to a switch.
It will run constantly or you can shut it off with the switch. The t-stats, on a call for heat will open the zone valves and the boiler will still run for your hot water. That's with the defective control.
 
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Old 02-03-14, 05:24 AM
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A properly piped and wired wood and oil set up, the sequence of operation on a thermostat call for heat should be ,(1) wood boiler temperature above oil boiler high limit setting and high enough that pump that circulates water to and from oil boiler is on , controlled by its own aquastat usually set at 130f .(2) oil boiler pump controlled by low limit usually set at 140f delivers heat to rooms. If the oil burner is disabled the low limit can be turned to it lowest setting and water below 140f can be circulated through oil boiler to rooms without causing condensation in boiler. Comfort of home is sacrificed as oil boiler becomes a place to store btus until needed.
 
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Old 02-03-14, 07:45 AM
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Comfort of home is sacrificed as oil boiler becomes a place to store btus until needed.
What do you mean by " Comfort of home is sacrificed ... " ?

What does storing BTU in the oil boiler have to do with sacrificing comfort?
 
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Old 02-03-14, 03:45 PM
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Looking at( comfort of home is sacrificed ) should have said may be sacrificed as high limit is set below 180f and may not be able to keep up with the heat loss from house.
 
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