Harman Magnum Stoker - Hot Water Coil Hookup for Hot Water?

Hi guys,

What type of heat exchanger should I use for the hot water tank?

I have an oil boiler which feeds into an Amtrol hot water tank for the house.

I have some idea of how the whole hookup should happen, but I could use some advise.

It seems like I need the exchanger on the return line from the Tank to the boiler, then the hot water will got into the boiler keeping it warm and then sending that hot water to the water tank.

This will/should prevent my boiler from kicking on if the temp is hot enough correct?

Hi beatle78, use the search function on the forum, and do a search for 'hot water coil' heating domestic hot water, and any variation of this you can think of.

There are at least a dozen threads with schematics, ideas and experiences.

It sounds like you have an 'indirect' hot water tank?? Using oil heated boiler water to heat the domestic hot water via an internal 'in tank' heat exhanger??

With a hot water loop in a coal stove, the water has to circulate, and needs to be heating a resevoir of water. This is because there will be water in the coil over the coal fire, but all night long there will be no hot water use, so the amount of water must be fairly large to keep it from getting to the boiling point.

We will need a schematic of your water piping for the boiler and heater.

greg L

OOPS! Greg beat me to it... what he said!:oops:

You could purchase a side arm heat exchanger (around $125 on ebay) and install it in the loop to the Amtrol which itself should be a heat exchanger providing hot water from the heat of the boiler water. You can circulate the water with a circ. pump or by thermal siphon.

I am getting ready to hook up an Amtrol tank/heat exchanger to my coal boiler to provide hot water for the house in connection with the Hydronic heating loop to the baseboard heat.

If you draw a schematic of the flow of your current set up with the Amtrol, I bet we could figure a way to hook that up with the coil on the stove (using the correct placement of check valves and interaction with the exisitng boiler controls) and save the purchase of an additional heat exchanger. And yes with this setup the boiler will not fire as long as the stove is providing enough hot water to maintain temp above the boiler fire temp (although that is not going to happen often, it most likely reduce the run time since you are adding btus).

Not sure I helped you out any with my ramblings, babbling, etc., but posting a schematic of how your existing boiler/Amtrol setup works will get the experts on the forum (of which I am not one!) thinking about how to set you up.

thanks guys!

I will do some searching on the forum, then I'll put together a schematic of my current setup along with questions!

You guys rock!

OK, I've been reading a lot on this forum.

Did I get screwed by my Harman dealer with my hot water coil?

My coil looks NOTHING like the other pics I've seen.

There are no windings whatsoever?????

Nope, that is the standard 'coil' it is actually a 'U'. The circular coils you may have seen on the forum are custom made ones. The 'U' shaped one is commercially available, on Ebay, in stove stores etc.

Greg L

.

ok, thanks.

Does that seem to be OK for those who have used it?

Or do most of the folks on here order a custom coil?

I think the U version works pretty good, I'd keep reading, there were several threads last season about this.

Take a look in the 'pictures of your stove' thread, and look for plumbing. I can't remember specific members or stoves. but there are quite a few.

greg L

Check your PM's

Thanks Greg!!!!

I just spent awhile on the phone with Greg getting some pointers for hooking up my water coil.

I've attached a pic of what we talked about.

What does everyone think?

Basically, the Stoker would plug into the feed line from the boiler to the domestic tank and the circulator pump would be wired to run 100% of the time.

This should heat the Domestic, run into the boiler, and then back to the Stoker.

See attached pic (pic drawn with Microsoft Visio)

Thanks,
Jeremy

ok, I just got home.

The circulator pump on the water tank is a Grundfos UP 15-42F. I didn't see the specs on their website for it.

Is this pump OK to run all the time?
I wonder if it's as energy efficient as a Taco 007 that Greg mentioned to me?

I found the spec for the Grundfos UP 15-42F.

I attached the complete spec here.

Here's the specs for the Taco 007.

TACO 007
Performance Data
Flow Range: 0-20 GPM
Head Range: 0-11 Feet
Minimum Fluid Temperature: 40º F (4º C)
Maximum Fluid Temperature, Cast Iron: 240º F (115º C)
Maximum Fluid Temperature, Bronze: 230º F (110º C)
Maximum Working Pressure: 125 PSI
Connection Sizes: 3/4”, 1”, 1-1/4”, 1-1/2” Flanged

Here's the specs for the Grundfos UP 15-42F

Grundfos UP 15-42F
FLOW RANGE: 0 to 20 gpm
HEAD RANGE: 0 to 16.5 feet
MOTOR: 2&4 pole, single phase
MAXIMUM FLUID TEMPERATURE
(Open Systems): 140°F (60°C)
(Closed Systems): 230°F (110°C)
MINIMUM FLUID TEMPERATURE: 50°F (10°C)
PRESSURE: 145 psi maximum (working)

As always the devil is in the details. I assume you are using your existing expansion tank and it's large enough for the additional stoker water capacity. If the Magnum Stoker is hot and both the supply and return valves are then closed there needs to be a path to the expansion tank. You can get around this need by shutting only one valve, waiting for the stoker to cool and then close the second valve. However it doesn't meet the plumbing code. You should have a thermostat in your hot water tank to control the domestic water heater circulator pump. Once the tank comes up to temperature it's a waste to keep it circulating. Put a temperature probe well on one of the heater fittings and use a single action aquastat and a circulator relay to control the pump.

Hi Yanche,

Thanks!!

[For the record. I'm new to heating so I may ask some simple/dumb questions!]

Yes, the expansion tank is existing and is a 43 GAL tank.

The tank has a thermostat in it now, but when it activates, it turns on the circulator pump and the boiler.

Should I turn down the thermostat that's connected to the boiler and install a second thermostat and make sure that it is set higher that the first thermostat?

Thanks,
Jeremy

When using coal boiler .... The coal boiler aquastat should control the boiler in whatever way the boiler manufacturer designed it to operate. The point is you have hot boiler water in standby at the high set point of the aquastat. When the hot water heater thermostat calls for heat because some hot water was used the circulating pump will turn on and raise the domestic hot water temperature to the set point. If the boiler water temperature is lowered the boiler aquastat will cause the coil boiler to make more hot water as needed.

When using your non coal boiler .... The non-coal boiler is normally cold. The hot water heater thermostat call for heat. The non-coal boiler turns on and reaches the low set point of the aquast. The hot water heater pump turns on. The non-coal boiler stays on until the high set point of the aquastat is reached or the hot water heater reaches it's high set point. This is the most economical way to control summertime use of a indirect hot water heater. It reduces the standby losses in the relatively poorly insulated boiler. There are some issues with cast iron boilers and firing them when cold, especially oil burners. My belief is this is not a problem when the summer boiler water temperature is the mild ambient temperature or warmer.

As you can see there are different control scenarios for summer and winter. I have a seasonal switch on my boilers which changes the control method. You do not need a second hot water heater thermostat.

Yanche, this is a simple loop of SS tube in the stoker stove, it has to have circulation all the time. Other wise the few gallons of water in the pipes will overheat and flash to steam

You mention the scenario of having the stoker hot and then shutting the valves, trapping the water in the coil, creating a bomb. Why would anyone do this?? Are you saying that it needs to be plumbed to be fool-proof to meet code?? Then an additional tee-off to the expansion tank and a PRV is in order

You also mention that once the water is up to temp it is a waste to keep the water circulating, but this is the drawback of installing a loop in a stove, you can't shut down the heat source, so you have to keep the water circulating, or you will create steam in the loop. So the circulation pump must keep running. Or if it was a gravity setup it would keep thermosiphoning.

The schematic that beatle posted is what we discussed.. I suggested this way so that he could run the coal stove all night long, and not have water overheating in the system. The indirect loop in the domestic tank will pass on the heat to the water, the oil boiler will stay warm to hot, and he will have recovered some heat from the coal stove and stored it in the hot water.

The valves as shown are to isolate the loop from the boiler and domestic hot water system durning the summer when the stoker stove will be cold.

As drawn, the quantity of water in the oil boiler may be too much to raise to an effective level to eliminate the oil burner from running, but even if it raises the water temp only 20-30* it is that much less oil burned to get up to effective temps.

Greg L