OWB not transfering heat into oil burner

[Mahoney86]

Here is a little more overall picture of the front of my oil boiler

So i think I’m going to scrap all of the 3/4” pipe. I’ll be out of town this weekend at my hunting cabin where I know I can get longer lengths of 1” pex. So I’ll change that piping from the OWB and plug 1” into the HX.

As far as the oil boiler side of the HX goes it sounds like I can get rid of the blue return line off the back of the oil boiler. Would I just be adding another T at the base of my boiler where I have the red supply pex? And just create a loop into the HX and back into a newly added T?

One of the biggest things I need to be able to do is very easily shut off the supply to the HX on the oil boiler side as I travel a lot for work and am in the mountains many weekends through winter. I want to be able to put the OWB in a by pass recirc mode easily and keep the oil boiler separate as to not waste oil heating the OWB while I’m not here

 

[Mahoney86]

Would something like this work? After I drew the sketch and looked at it more I am thinking it would not work because I am adding a line to the HX before the recirculating pump and likely will cause cavitation issues? Can I make all my connections to the HX at the bottom Tee of the Oil Boiler?

 

[stee6043]

Would something like this work? After I drew the sketch and looked at it more I am thinking it would not work because I am adding a line to the HX before the recirculating pump and likely will cause cavitation issues? Can I make all my connections to the HX at the bottom Tee of the Oil Boiler?

That won't work. You can tee into the return line where you have it marked but you need to come back into that line (from the HX) upstream of the existing circ pump. The way you have it drawn now is eliminating the pump from the circuit which will not work. You want your existing oil boiler circ pump to pull supply from the house, send it through the HX, and then send it back through the oil boiler the way it currently does it. This way your oil boiler can effectively work as a backup. And your plumbing is sure to work.

The bypass you have drawn will work if you need to run the OWB pump while away for work. Make sure you're using full port ball valves for those shutoffs.

 

[stee6043]

The problem you're struggling with is that you will need to cut some pipe. Not ideal for the average DIYer (at least not me). You can get black pipe cut and threaded and Home Depot and Lowes. Probably Menards too. I'd recommend you modify that piece of pipe between the ball valve and your existing pump. Add two tee's with another ball valve between them and you're set.

Your existing ball valves are perfectly placed to enable this work. You can make this modification without draining the whole system. You will, however, end up with air in there after you're done.

 

[Mahoney86]

I actually do not think that will be terrible to do. I have ample amount of copper above that valve and circ pump. I cannot braze for the life of me, but I can install sharkbite fittings and install copper pipe with (2) Ts on it before that circ pump. I don't think I would modify the pipe after the valve as its 1 1/4" black iron, the copper above would be fairly easy to do.

 

[stee6043]

I actually do not think that will be terrible to do. I have ample amount of copper above that valve and circ pump. I cannot braze for the life of me, but I can install sharkbite fittings and install copper pipe with (2) Ts on it before that circ pump. I don't think I would modify the pipe after the valve as its 1 1/4" black iron, the copper above would be fairly easy to do.

Let us know how it goes! Make sure you put a shutoff between those two tee's. You'll need to have a way to force the flow into the HX once installed.

And if you do end up needing to do some work on the black pipe it's really not that bad. But you'll need two pipe wrenches and some pipe dope. Lowes/HD can cut and thread to size. But yeah....shark bites are slick, though not cheap.

 

[Mahoney86]

Finally getting around to putting the HX on and before I go cutting up copper, I have a thought that I’m not sure this is all going to work as planned.

In my original posts I mentioned the oil burner also heats my DHW. If I plumb the HX into my return side of my oil burner ( before the circulating pump) won’t my oil burner get cold and ultimately loose hot water temp enough that my oil burner will fire? This creates another problem for me as I will have my hi/lo on the oil burner set low so I don’t see myself having any nice long hot showers.

Please tell me I’m wrong or if I should rethink my plumbing connections prior to hooking the HX up

 

[stee6043]

Finally getting around to putting the HX on and before I go cutting up copper, I have a thought that I’m not sure this is all going to work as planned.

In my original posts I mentioned the oil burner also heats my DHW. If I plumb the HX into my return side of my oil burner ( before the circulating pump) won’t my oil burner get cold and ultimately loose hot water temp enough that my oil burner will fire? This creates another problem for me as I will have my hi/lo on the oil burner set low so I don’t see myself having any nice long hot showers.

Please tell me I’m wrong or if I should rethink my plumbing connections prior to hooking the HX up

You're wrong .

The circ pump on your boiler is pulling return water from your home and pushing it back into the boiler, correct? It should be. If it's plumbed correctly once you add the HX to the return side your circ is going to pull return water from your home, send it through the new HX (which will heat the water above the set point for the boiler) and then send it thru the oil boiler and back to the rest of the house. The flat plate will heat the water, the oil boiler will not need to fire unless your wood burner burns out.

 

[Mahoney86]

Correct the circulating pump is pulling return water from my baseboard system. One my house thermostat calls for heat the circulating pump kicks on.

However my DHW supply is all seperate connections and is fed from my well pump.

I guess I am struggling to understand how the oil boiler will stay hot unless I am actively circulating how water from my OWB through the oil burner and into my base board system

 

[maple1]

Correct the circulating pump is pulling return water from my baseboard system. One my house thermostat calls for heat the circulating pump kicks on.

However my DHW supply is all seperate connections and is fed from my well pump.

I guess I am struggling to understand how the oil boiler will stay hot unless I am actively circulating how water from my OWB through the oil burner and into my base board system

Well, the assumption is that your house will be needing heat quite often. During which times the HX should heat your oil boiler well above the oil burner setpoint.

If everything sits there for long periods not doing anything to heat the house, then yes your oil boiler would cool off and cut in. The same way it would right now before you make any changes.

 

[mustash29]

You will need to plumb it as follows.

Loop 1 - Wood boiler to HX.
Loop 2 - Other side of HX to oil boiler jacket. Both of these pumps need to run 24/7.
Loop 3 - Normal oil boiler, air separator, expansion tank, zone valves, pump, house heating loads, etc.

With this setup you run the wood pump when you have a wood fire. Heat is transferred through the HX and the 2nd loop keeps the oil boiler jacket (and your internal DHW coil) in hot standby. When a zone calls for heat the oil boiler distributes it like normal. If anything goes wrong (no wood fire, pump 1 or 2 fails, etc.) then the oil kicks on in backup.

 

[Roundgunner]

I have a double set up (2 houses and now an apartment) just like Mustash 29 describes above in service for 5 years now. I also use the return water from the big house to heat the new 1200 SF apartment above the garage. It is a complicated diagram but it may help.

 

[Roundgunner]

I do have a lot of flow, lots of pumps.

 

[Roundgunner]

The manafolds. It is a big house and it gets plenty cold here.

 

[Mahoney86]

I am going to have to figure out the additional pump to keep the oil boiler water jacket warm as the oil boiler definitely kicks on whenever the demand for hot DW is needed.

Before I do that I still need to figure out much more on the wood boiler side.

1) very hard to keep adequate coal bed as I can get the water temp up to 195 in under an hour. This in turn leads to the fire going out each night for the last 3 nights, but wake up to a full load of wood in the boiler. I’m splitting my normal size wood even smaller to try and get it to burn down to coals quick. I’m burninb locust right now that’s 18% moisture after a fresh split.

2) wood boiler keeps going into Hi Temp mode (200+ degrees) which is one of the major reasons I also can’t develop a coal bed. The wood boiler stops all functions until the temperature drops.

3) despite the hi temp going off, my cheapo laser thermometer only reads 178 degree on the OWB supply line pex right at the heat exchanger. Return line temp reads 176.

Right now my OWB is set for a high temp of 195 and low of 185 with a differential of 10. I also have it set for every 20 minutes to give a 60 second pulse of air which likely doesn’t happen since I’m in and out of hi temp mode.

I figured yesterday would be a struggle as the temperature outside was up in the mid 40s but was very surprised to wake up this morning to fire being out, the wood I put in last night barely chared and the fire being completely out. Sounds like the oil burner likely ran all night. It was down in the low 30s last night

 

[maple1]

If you aren't moving the heatout of it, that will all happen.

So sounds like you should get that part figured out, and the wood boiler is doing ok. Or ok enough to demand the moving heat out issue is current issue 1.

 

[Mahoney86]

Any ideas as to why the heat isn’t moving out? I’ve pushed domestic water via a garden house through the OWB lines from the heat exchanger out.

My house is getting heated as the oil boiler didn’t run at all during the day yesterday and I brought the house up to 70. All the lines are now 1” pex.

 

[stee6043]

Did you install the flat plate yet? Your plumbing (using the overpressure for return) is the reason you're not moving heat. I thought that part of the mystery was solved

 

[maple1]

You should update as to what changes have been made since the first posts and pics.

 

[maple1]

Any ideas as to why the heat isn’t moving out? I’ve pushed domestic water via a garden house through the OWB lines from the heat exchanger out.

My house is getting heated as the oil boiler didn’t run at all during the day yesterday and I brought the house up to 70. All the lines are now 1” pex.

Some conflicting info posted. Here saying oil not cutting in at all during day, prior post saying definitely cuts in for DHW.

 

[Mahoney86]

To clarify I did not hear the oil boiler run at all yesterday until my wife took a shower and there was a demand for domestic hot water. Other then that I did not hear the oil boiler run until I woke up this morning to the OWB fire out.

Attached is my latest changes to the system. I installed (2) Tees and a ball valve on my base board/oil boiler return line. Right now the Ball valve is closed forcing water to go directly into the bottom of the heat exchanger. It then comes out the top of the heat exchanger and goes right into the oil boiler circulator pump.

The OWB boiler lines have all been upgraded to 1” pex going directly into the heat exchanger. The OWB supply goes into the top and the return into the bottom. I installed purge valves on each line and also also Teed the 2 lines together with a ball valve to bypass the heat exchanger if needed. Disregard the old 3/4” pex as I haven’t tore it all down yet

 

[warno]

What are the dimensions of your plate heat exchanger? Plate count and HxWxL measurements?

Do you know how many GPM your OWB side is running? And how many GPM your oil boiler is running?

If you are only getting a delta T of 2° through your FPHX you definitely have a flow issue. Even though your HX looks small you should see more than 2°.

 

[Mahoney86]

Heat exchanger is 5x12 and 20 plates with 1 1/4” fittings. It’s supposed to be rated for 330,000BTU

Not sure about the flow on either but I do know I have a much larger pump on my oil burner

 

[warno]

Is there anyway you can check the flow on OWB side? Possibly unhooking the return line and running into a bucket while timing it.

Pump size dimensionally doesn't mean a whole lot. I'm wondering if you possibly have an air lock somewhere on the OWB side. Mine just had that problem the other day. I had really low delta Ts and the pump was making alot of noise because it was stuck in an air bubble. If you have an air pocket somewhere that holds up flow you will have this problem.

How did you go about purging the wood boiler side? Also I can't remember for sure the rules about the FPHX but I thought they were supposed to stand up if at all possible.

 

[Mahoney86]

Little day after Christmas update. So Christmas Eve I turned my oil burner hi down to 145 and low of 140, I figured let me turn this thing down as low as it can go. I also turned my OWB to a hi temp of 190 with a 10 degree differential. It is also supply a 60 second puff of air every 10 minutes to keep the coals going.

So I woke up Christmas morning to a warm house (68*) and to my amazement when I looked outside heat was coming from the OWB chimney. I went outside to check and a beautiful bed of glowing coals and all the wood had burned down. So far this has been the case each morning where today I almost lost the coal bed with how well it burned down!

There are still a few issues I can’t seem to figure out. With lowering the OWB hi temp, I have solved the issues of the OWB going into Hi Temp mode, but the water coming into my heat exchanger is now even colder (168-172 degrees as compared to 178-180 when I had the OWB set to 195 degrees). I still find it hard to believe with thermopex buried 2’ underground that I’m loosing 20+ degrees temp on only a 75’ run when outside air temps are in the low 40s.

This brings to my next issue that the 168-172 OWB supply lines are only keeping my oil burner lines around 150-156 degrees, hence the reason why I now have my oil burner set points so low. Otherwise the oil burner drops below the 145 set point. I do have 10’ of OWB supply and return lines ( in my badement) that are not insulted which could certainly be part of the problem but would I really lose 20* or temp?