Honeywell L8148A Aquastat Relay

[markpee]

I'm in my basement right now with the oil burner running. Yeah, I did it - I fired it up. I have the L8148A aquastat controller hooked to my Weil-McLain 140k BTU boiler and what I'm trying to do is help the EKO maintain the temp for a while while I do some analysis - as my heat got so low last night it would have taken all day for the wood unit to get the house warm again. The wife is home on materiney leave until at least January, but I'm worried that once she goes back to work, especially in the coldest months of the year, we may need oil to back up the house heat.

So here's my problem. The L8148 only has a "high limit", and its lowest setting is 180 degrees, not sure what the differential is. I would rather have a relay that comes on when the boiler temp gets much lower than that - perhaps 120? I can sustain hot water (75 gallon tank) at 120 and can get the house to temp and maintain it between 140-150. Is there a way to do this with an add on (the sticker on the stat mentions a series 60 control but nowhere can I find out details on it).? Or should I change the relay? To what? Searching through back posts, it is apparent that perhaps I should re-plumb in parallel instead of in series, as I have huge heat loss through the chimney on the oil boiler...

As I'm typing, the boiler shut off at 180 and its now down to 170 and hasn't come back on yet.

So I guess my short quesiton is about a new or add on unit to control the oil boiler the way I want. Keep in mind that my Oil boiler and EKO are seperated by about 150 feet.

 

[kevindauch]

Hi Mark,
I'm not in the HVAC business, but here is my take:
I believe that the 8148A has a high limit differential of 8 degrees and the 8148E has high limit differential set at 15 degrees. I'm not sure why you are seeing a problem with the EKO heating the house, are your lines well insulated? Anyway, I'm not sure how you have the EKO and the Weil-McLain plumbed but, you could add a close on fall aquastat to your EKO and wire it up in series to your zone controller output to the TT terminals on the 8148A. That way when the EKO is below a preset temp and there is a demand for heat, the oil boiler will come on, if you have it plumbed that way (primary secondary). You will probably have to control the circulator for the EKO too. If you have the boilers plumbed in parallel, then you can just use the 8148 to control the oil burner. The EKO's output will be circulated to the oil boiler.

 

[BrownianHeatingTech]

An 8148A should have a fixed 8 degree differential.

It should be adjustable down to 120 degrees, as well. Take a close look at it, and see if there's a movable stop in place (the scale should obviously go down to 120 degrees), and move the stop to allow further movement.

There are some obsolete models which may not be able to go that low (I can verify if you get the last four digits: L8148Axxxx), so check the scale on the dial to be sure.

Joe

 

[u4015]

I just found this. see if it is of use

(broken link removed to http://www.inspect-ny.com/heat/Aquastats.htm)

Later

Bob

 

[markpee]

Hi Mark,
I'm not in the HVAC business, but here is my take:
I believe that the 8148A has a high limit differential of 8 degrees and the 8148E has high limit differential set at 15 degrees. I'm not sure why you are seeing a problem with the EKO heating the house, are your lines well insulated? Anyway, I'm not sure how you have the EKO and the Weil-McLain plumbed but, you could add a close on fall aquastat to your EKO and wire it up in series to your zone controller output to the TT terminals on the 8148A. That way when the EKO is below a preset temp and there is a demand for heat, the oil boiler will come on, if you have it plumbed that way (primary secondary). You will probably have to control the circulator for the EKO too. If you have the boilers plumbed in parallel, then you can just use the 8148 to control the oil burner. The EKO's output will be circulated to the oil boiler.

I would like to see a more detailed explanation of your scheme - I almost get it. Would I leave the controller hooked up to the 2001A on the EKO or are you suggesting using the 8148?

 

[RJP Electric]

The 8148 is a cold start relay and will not run (the oil) unless a zone is calling. When it reaches its high limit that's when it will shut down the oil. Here is the link to Honeywell to answer your questions. regarding temp and differential.

My boiler is in series like yours, I wouldn't have it any other way! The biomass heats up the block of the oil boiler, when the block of the oil is up to temp (150*) the main circulator shuts down and the hot block feeds the zones so the biomass can go back to charging the storage. *EDIT* Plus there is a zone valve in line also with that main circulator. It opens only when a zone calls too.



http://customer.honeywell.com/techlit/pdf/PackedLit/95-6940.pdf

 

[BrownianHeatingTech]

My boiler is in series like yours, I wouldn't have it any other way! The biomass heats up the block of the oil boiler, when the block of the oil is up to temp (150*) the main circulator shuts down and the hot block feeds the zones so the biomass can go back to charging the storage.

You can accomplish that with a diverter valve, or an electronic control (variable-speed mixing control), which will allow the zones and the storage to charge at the same time. That avoids wasting energy heating the oil boiler's block (especially important if you run the wood for hot water during the summer).

Not that the brute force approach doesn't work, but there are others ways to achieve the same thing.

Joe

 

[RJP Electric]

Thanks Joe! Thats Funny! I live in a drafty log home with crappy windows, an extra log or two won't kill me to heat the block. I like to keep things simple in my life. I love it! I have a Rheem marathon electric HW heater I use in the summer too I bought off the NHECO

 

[kevindauch]

Hi Mark,
If your wood boiler is hooked up in series with your oil boiler, then the output of the wood boiler goes into the oil boiler. A circulator (usually on the return side of the wood boiler) is controlled by a 4006 aquastat on the wood boiler, sends the hot water from the wood boiler into the oil boiler when a preset temp has been reached, say 165 degrees. The aquastat on your oil boiler (8148) turns on the oil if there is a requirement for heat and the temp of the oil burner is below the high limit - the differential temp. i.e. Your 8145 is set to 180 and the differential is 15 degrees, the oil will not come on until the boiler temp goes below 165 degrees.
For a primary/secondary hookup, the manifold is shared by both the wood and the oil boiler. Weighted check valves are installed on both oil & wood boiler outputs. In this case you have a 4008 aquastat on the wood boiler set to 165 for the previous example. Wire one side of the TT from the zone controller to the 4008 and then to the 8145. This way when your wood boiler is below 165 and there is a call for heat, your oil boiler will respond. If the wood boiler is above 165, and there is a call for heat, the 6008 will break the circuit, and the oil boiler will not start.
I hope that this helps a bit. I can draw a pic if you want.

 

[rowerwet]

my furnace had the same type of honewell aquastat it only went down to 180*, I found Home depot carries a newer version of this aquastat that goes down to 140*, it was very easy to change ( one screw and a good tug on the temp bulb besides the wiring) and now I have an aquastat that keeps the furnace off when my pellet boiler is going. CB wants the aquastat set to 120* but 140* works fine. In fact I left the aquastat set to 160* for a while and the furnace never fired. Right now I have my pellet boiler off as I am burning waste kerosene I get free at work and I am saving my pellets until I only have 200 gal left.
If you have the same aquastat as I had you can change it yourself for $125 or so from home depot.

 

[Grover59]

I set mine up with an aquastat on the loop going between the wood boiler and oil boiler, this aquastat is set at about 180, I can adjust the diff, and it is set to 10. This aquastat is the strap on type, or should I say I made it that way. This aquastat is just another switch in the thermostat loop and will not allow the burner to kick in if the temp is up. Most of the time I am heating the house with the tank, but when I build a fire and the temp is up on the boiler loop, and if the house calls for heat, the ciculator will start on the oil boiler and put heat in the house with the baseboard along with the floor heat. Once the themostats are satisfied and the house is heated, and the boiler loop continues to climb, I have another aquastat set at about 185-190 and this will start the pump to the loop to charge the storage, the wood boiler will not shut down unless the timer takes it down or the High High limit shuts it down, or power outage.

Steve

 

[markpee]

Hi Mark,
If your wood boiler is hooked up in series with your oil boiler, then the output of the wood boiler goes into the oil boiler. A circulator (usually on the return side of the wood boiler) is controlled by a 4006 aquastat on the wood boiler, sends the hot water from the wood boiler into the oil boiler when a preset temp has been reached, say 165 degrees. The aquastat on your oil boiler (8148) turns on the oil if there is a requirement for heat and the temp of the oil burner is below the high limit - the differential temp. i.e. Your 8145 is set to 180 and the differential is 15 degrees, the oil will not come on until the boiler temp goes below 165 degrees.
For a primary/secondary hookup, the manifold is shared by both the wood and the oil boiler. Weighted check valves are installed on both oil & wood boiler outputs. In this case you have a 4008 aquastat on the wood boiler set to 165 for the previous example. Wire one side of the TT from the zone controller to the 4008 and then to the 8145. This way when your wood boiler is below 165 and there is a call for heat, your oil boiler will respond. If the wood boiler is above 165, and there is a call for heat, the 6008 will break the circuit, and the oil boiler will not start.
I hope that this helps a bit. I can draw a pic if you want.

Thanks for the info - a pic is not necesary. The first example is how I have mine set up, however, I don't want the boiler to kick on until it gets real low, as I can sustain heat in the house at lower temps than the oil burner wants to be at. I'm thinking that when I do storage I might want to change over to a parallel setup.