Boiler Piping Design & Control Help - Froling S3

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Newfiestang

Member
Jan 5, 2017
133
NL
Folks,

been on here lurking and studying for some time now in an attempt to try and absorb as much info as i can before going ahead with this upgrade. Ive decided to go with Froling S3 and I've been working with the Canadian supplier in figuring it all out but i still have some questions that i prefer not to bother them with. I'm starting to feel I've taken up alot of their time but still haven't purchased. The Froling will replace an aging New Yorker WF100 wood boiler connected to the existing oil boiler.

So attached is the piping design we arrived at so far. As you can see I am trying to incorporate an existing oil boiler....which is the part i am struggling with. In the dwg you can see a 3-way valve which basically selects if the oil boiler sees water flow or not. The position of this valve is determined by the S3 based on water temp in the S3 and buffer tanks. The S3 will also electrically lock out the oil burner when this temp is above setpoint as well. This is all fine and makes perfect sense but my concern is that the oil boiler temp will continue to drop to ambient temp while wood is priority. My understanding of this configuration is, if the oil boiler is then called upon for heat it will now have to recover from ambient before heat to zones or DHW tank is at desired temp. This approach dont seem most practical or efficient unless im missing something here.

So two concerns, will this lag time pose an issue, and also, is there a possibility of a condensation issue in the boiler. From what I can tell there is about 25 gal of water in the oil boiler.

Do you guys have ideas for a better approach for the piping of this system?

Any help will be appreciated.

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salecker

Minister of Fire
Aug 22, 2010
1,479
Northern Canada
Hi i have a wood boiler system with oil back up
But i use a HX and my system is in a building by it's self.
My oil boiler is plumbed in to the house side of my HX the main feed going to the house has close spaced tee's where the oil boiler feeds and gets it's return.if i know i am going to be gone while the oil boiler is running i will close a valve on the wood boiler side of the HX to avoid any ghost flows that will send BTU's to the storage tanks.
If you look at my profile pic you can see the closed spaced tees before the pump that face down with the 90's with nothing hooked to them.It was take before i was finished
 

Newfiestang

Member
Jan 5, 2017
133
NL
Hi i have a wood boiler system with oil back up
But i use a HX and my system is in a building by it's self.
My oil boiler is plumbed in to the house side of my HX the main feed going to the house has close spaced tee's where the oil boiler feeds and gets it's return.if i know i am going to be gone while the oil boiler is running i will close a valve on the wood boiler side of the HX to avoid any ghost flows that will send BTU's to the storage tanks.
If you look at my profile pic you can see the closed spaced tees before the pump that face down with the 90's with nothing hooked to them.It was take before i was finished
Thanks for the info Salecker. Hoping someone chimes in with a similar system that can also add some advice.
 

ABMax24

Minister of Fire
Sep 18, 2019
1,086
Grande Prairie, Alberta, Canada
The way I see that schematic your oil boiler will always be as warm as the return side of your system, it won't go as cold as room temp.

The oil system is still the primary loop, as such there will always be water circulating through the oil boiler. Now when the S3 is on an additional pump pushes water through the wood system heating it and taking it back to the primary loop downstream of the boiler.

I don't see the 3 way valve you are talking about to select between the 2 boilers, I see a pump to push through the wood boiler loop, but no valve.
 

Newfiestang

Member
Jan 5, 2017
133
NL
The way I see that schematic your oil boiler will always be as warm as the return side of your system, it won't go as cold as room temp.

The oil system is still the primary loop, as such there will always be water circulating through the oil boiler. Now when the S3 is on an additional pump pushes water through the wood system heating it and taking it back to the primary loop downstream of the boiler.

I don't see the 3 way valve you are talking about to select between the 2 boilers, I see a pump to push through the wood boiler loop, but no valve.
The 3-way valve is on the boiler return water side. labeled as "pump 1" because it will be controlled by pump1 program in the Froling. When the wood boiler and buffer water temp is at or above setpoint in the S3 this 3-way valve will be closed to the oil boiler but open to the wood boiler return piping.

Hope this clarifies it.
 

maple1

Minister of Fire
Sep 15, 2011
10,796
Nova Scotia
I dont know what you have for an oil boiler but I dont really see an issue with it going cold (as long as it doesnt leak), and it should heat from cold quite fast.
 

Newfiestang

Member
Jan 5, 2017
133
NL
I dont know what you have for an oil boiler but I dont really see an issue with it going cold (as long as it doesnt leak), and it should heat from cold quite fast.
From reading on here it is often discussed about condensation issues with boiler water temps running to low. Im far from versed on all this so maybe your correct and there is actually nothing to be concerned about. Figured id ask.
 

maple1

Minister of Fire
Sep 15, 2011
10,796
Nova Scotia
From reading on here it is often discussed about condensation issues with boiler water temps running to low. Im far from versed on all this so maybe your correct and there is actually nothing to be concerned about. Figured id ask.

That, I think, refers to wood boilers, and cool return water causing bad creosote condensation in the firebox.

Some older oil boilers can spring small leaks or seeps when they go stone cold. Mine used to but that was around the domestic coil gaskets.
 
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Newfiestang

Member
Jan 5, 2017
133
NL
That, I think, refers to wood boilers, and cool return water causing bad creosote condensation in the firebox.

Some older oil boilers can spring small leaks or seeps when they go stone cold. Mine used to but that was around the domestic coil gaskets.
Pretty sure condensation can form in an oil boiler the same way.
 

Newfiestang

Member
Jan 5, 2017
133
NL
Is there anyone here familiar with wiring the froling core module, Im trying to find where the Boiler 2 signal terminates on the aux boiler. Im assuming it would terminate on the TT (thermostat) of the oil boiler aquastat but not sure. It is my understanding that the S3 will use this signal to disable the oil boiler when wood boiler temp is above setpoint.....but not 100% sure. If this is the case im also assuming that the S3 core module can accept 24VAC as i think this voltage will be present on the oil boiler aquastat. All questions at this pint.

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maple1

Minister of Fire
Sep 15, 2011
10,796
Nova Scotia
Pretty sure condensation can form in an oil boiler the same way.

Not in the same way as wood boiler with a fire in it. There is the heat from the fire plus the cold from the return water plus the condensing dirties and moisture in the wood smoke. A cold oil boiler would not have the fire or the dirties to condense or moisture in the fuel and likely not the cold water coming in since that should be going through the wood boiler.
 

salecker

Minister of Fire
Aug 22, 2010
1,479
Northern Canada
My backup oil boiler sits cold till it is required,it is also under pressure.
Going on the 11th year and zero issues.It was a used unit that i got cheap with a box of spare parts.
 

Newfiestang

Member
Jan 5, 2017
133
NL
My backup oil boiler sits cold till it is required, it is also under pressure.
Going on the 11th year and zero issues. It was a used unit that i got cheap with a box of spare parts.
Salecker, is your wiring such that your wood boiler locks out your oil boiler. If so how do you have it done, it seems from your comment that you actually have it such that its eclectically isolated via relay or similar since your boiler goes cold. Im now hoping that i can just disable it via the Froling "boiler" signal to the TT on the oil boiler aquastat. By using this method the oil boiler aquastat remains powered and can maintain min boiler temp via the low limit setting on the aquastat. That is actually currently what happens during the summer months when the house dont call for heat, the boilers still maintains a min temp using this setting. See pic below of oil boiler aquastat, its a Honeywell L8124A dual.

As mentioned above im just not sure what the "boiler" signal on the Froling is designed to see as voltage since the TT terminals on the oil boiler aquastat does have 24VAC between the terminals.

1604858116108.png

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salecker

Minister of Fire
Aug 22, 2010
1,479
Northern Canada
I have a aquastat on the feed line to my HX from storage,when the temp drops below 110 it switches off the the pump supplying the HX and fires up the oil boiler.
At the time that happens the wood boiler has been shut down for hours already.
 

Marshy

Minister of Fire
Dec 29, 2016
824
NY
Folks,

been on here lurking and studying for some time now in an attempt to try and absorb as much info as i can before going ahead with this upgrade. Ive decided to go with Froling S3 and I've been working with the Canadian supplier in figuring it all out but i still have some questions that i prefer not to bother them with. I'm starting to feel I've taken up alot of their time but still haven't purchased. The Froling will replace an aging New Yorker WF100 wood boiler connected to the existing oil boiler.

So attached is the piping design we arrived at so far. As you can see I am trying to incorporate an existing oil boiler....which is the part i am struggling with. In the dwg you can see a 3-way valve which basically selects if the oil boiler sees water flow or not. The position of this valve is determined by the S3 based on water temp in the S3 and buffer tanks. The S3 will also electrically lock out the oil burner when this temp is above setpoint as well. This is all fine and makes perfect sense but my concern is that the oil boiler temp will continue to drop to ambient temp while wood is priority. My understanding of this configuration is, if the oil boiler is then called upon for heat it will now have to recover from ambient before heat to zones or DHW tank is at desired temp. This approach dont seem most practical or efficient unless im missing something here.

So two concerns, will this lag time pose an issue, and also, is there a possibility of a condensation issue in the boiler. From what I can tell there is about 25 gal of water in the oil boiler.

Do you guys have ideas for a better approach for the piping of this system?

Any help will be appreciated.
I have a very similar setup as yours except I have the FHG boiler which is the predecessor to the S3. I bought one of the very last FHG's to come to the US and the boiler was constructed as an S3 but the controls are FHG... Anyways, I have an external (BLT) controller that determines if the oil boiler should be fired when the storage temp drops to a predetermined temperature.

First, you are correct, the oil boiler does cool off to the point it reaches room temperature. However, the lag time for the oil boiler to get up to temperature is not very long from my experience and I have no noticed any condensation or other negative consequences from operating in such a manner. In fact, I have the setpoint to switch to the oil so low that it becomes obvious the storage tank needs recharging before the oil boiler will fire. When I'm in the groove of using the boiler I want 100% load be handled by the wood boiler.

I have the BLT controller set to switch to oil boiler with a storage tank temp of 120. There's hardly any usable heat to my baseboard heater below about 140F so I usually notice if the storage is depleted very easily.

In my opinion, there would be a larger net loss of efficiency and energy by some how maintaining a minimum temperature within the oil boiler. Some of that heat in the oil boiler will go up the chimney while in standby so I think its best if it sits at room temperature personally.

I did a detailed installation thread on this forum. You can see the piping diagram I used to connect to my boiler and I have actual pictures of the constructed piping. https://www.hearth.com/talk/threads/froling-add-on-install.163423/
Please let me know if you have any questions I would be happy to help you if I can. Send me a message and I will get an email notification.
 
Last edited:

Case1030

Feeling the Heat
Dec 12, 2017
365
Manitoba
After talking to a few heating professionals using all black iron makes for a pretty clean install.
 

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