Instant Hot Water Heater to Replace Tired Oil Burner Hot Water Coil

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Old 03-30-15, 11:47 AM
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Instant Hot Water Heater to Replace Tired Oil Burner Hot Water Coil

Could I please get a sanity check on my setup before I get going with the torch? The HW coil on my oil burner had been on it's way out for years. I recently picked up one of those instant HW systems.

It seems simple enough but I want to make sure I'm not overlooking anything.


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First, I'm planning to T off the cold water inlet and have a line go to the instant HW unit. Also cut the hot water line to the house where the dashed red line is on the top and have the instant HW output there.

Next, cut the coil out (bottom dashed line) and leave that open. I'm guessing I would have to crank down the water aqua-stat to prevent the burner from kicking on?

Then the cut in the middle (by the supply the heating system) - should this be capped or would I need a drain? Is that red pressure reducing unit in the middle a check valve as well?
 
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Old 03-30-15, 04:51 PM
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You sound reasonably sane to me... but I may not be the best judge of that!

Next, cut the coil out (bottom dashed line) and leave that open.
Yes, you don't want to seal it, but you can slip caps over the cut ends of the pipes for a better look.

I'm guessing I would have to crank down the water aqua-stat to prevent the burner from kicking on?
This is a whole 'nother story... yes, you can crank the LOW all the way down, but you may be able to easily modify the aquastat for a 'cold start' boiler as well.

What make/model aquastat is installed?

Then the cut in the middle (by the supply the heating system) - should this be capped or would I need a drain? Is that red pressure reducing unit in the middle a check valve as well?
It wouldn't hurt to have a hose bib there to flush the line from time to time. Those 'dead ends' in plumbing systems can build up 'crud' and it's a nice place for the water-borne pathogens to live and breed.

Honestly though, once you cut and YES, either cap or valve, that pipe, it's going to be flopping around in the breeze. I myself would re-do that part completely.

There is a 'check valve' of sorts in the pressure reducing valve, but most modern codes also require a BACKFLOW PREVENTER on the domestic side of the pressure reducing valve.

If that water hammer coil was needed at one time, it may still be needed... you might consider relocating that and keeping it in service.
 
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Old 03-31-15, 06:23 AM
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Thank NJT!
Here is the aquastat - it's a Honeywell:
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Now, I'm still using the burner for heating. It's set to 180 - does the controller just monitor the overall temperature of the boiler and not segregate between heating and HW? For example, running the heating circulator or requesting hot water would take heat away from the boiler and the aquastat would try to always maintain the 180 - just trying to wrap my head around the system. If that's true - would I simply do nothing with the setting on the aquastat?

I'd also be tempted to turn the burner off in the summer when there is no call for heat but I'm guessing it would just leak all over the place - maybe turn the setting down?

Do you really thing that water hammer thing is doing anything? And why would it be just on the hot side?

Thanks Again!!
 
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Old 04-01-15, 03:16 PM
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What's the model number of the boiler?

does the controller just monitor the overall temperature of the boiler and not segregate between heating and HW?
When you say 'controller', you are talking about the aquastat and not the "Heat Mangler" attachment, right?

What that aquastat does is always maintain the boiler at the LOW setting, which should be say 140-150 or so. When there is a HEAT CALL, that LOW setting is over-ridden and the boiler can fire up to the HIGH setting, which should be 180 or so.

That's the 'basic' operation.

The "Heat Mangler" attachment does some funny stuff though... we'll not go into that at this time.

You said the HIGH is on 180, what do you have the LOW setting on?

For example, running the heating circulator or requesting hot water would take heat away from the boiler and the aquastat would try to always maintain the 180 - just trying to wrap my head around the system.
As above, when there is NO heat call, the pump will of course not run, the boiler will maintain the LOW setting to make hot domestic water.

If that's true - would I simply do nothing with the setting on the aquastat?
If you did nothing, the boiler would still maintain at the LOW setting.

I'd also be tempted to turn the burner off in the summer when there is no call for heat but I'm guessing it would just leak all over the place - maybe turn the setting down?
I would be very tempted to do that also. Why burn fuel keeping the boiler at the LOW setting during the summer? (also adding heat load to your A/C system).

It MIGHT leak... but it might NOT! You won't know until you try it.

Do you really thing that water hammer thing is doing anything? And why would it be just on the hot side?
I'm sure it's doing something. Keep in mind that even though it's on the HOT side, it's still 'communicating' with the cold side... through the boiler coil, to the COLD side.

Somebody installed it for some reason... fast closing valves such as washing machines, dishwashers, sometimes toilets, can cause water hammer.
 
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Old 04-03-15, 08:16 AM
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Boiler is a Utica OBT 4.

I'm not considering the "Heat Mangler" in the equation - it's a nice looking paperweight as far as I'm concerned.

The left side of the aquastat is set to 180 and the right 140. The burner was reading 180. With no call for heat, shouldn't it be closer to 140 then? Since I won't be making hot water out of it, would you recommend a different temperature range?

When I get it all setup, I'll gradually turn back the setting on the aquastat and check for leaks.

As for the hammer arrestor - I'm thinking I'll throw a threaded T somewhere and put one of the newer ones with with the air bladders.

Thanks Again!!
 
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Old 04-03-15, 03:05 PM
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The left side of the aquastat is set to 180 and the right 140. The burner was reading 180. With no call for heat, shouldn't it be closer to 140 then? Since I won't be making hot water out of it, would you recommend a different temperature range?
Could be a few things going on here...

a: inaccurate thermometer

b: inaccurate aquastat (possibly the sensing bulb not fully inserted, or poor thermal contact inside the well)

c: "heat soak" driving the water temperature up after the burner fired and correctly sensed and shut off at/near 140F. It's not inconceivable to me that a boiler with high mass could store enough heat in the cast iron after firing to cause a 30-40F temp rise after the burner shuts down.

As for the hammer arrestor - I'm thinking I'll throw a threaded T somewhere and put one of the newer ones with with the air bladders.
You mean an expansion tank? or one of the copper tubes with the air inside?
 
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Old 04-03-15, 03:09 PM
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Looks like your boiler pre-dates anything on their website... no manual there.

Is there a wiring diagram on the inside cover that you can perhaps photograph clearly enough to be readable?

One thing I think you are going to need to do is disconnect the sensor from the heat mangler that tells it domestic hot water is being used.
 
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Old 04-07-15, 11:59 AM
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Here is the diagram - when setting up the "Heat Mangler" I had asked Utica for a copy.

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Yes - you are definitely right about unhooking the sensor.

As for the water hammer - I was thinking one of these:
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Thank-You!
 
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Old 04-07-15, 12:51 PM
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But.......

What you show in the boiler pic is not an R8182 control?



Yes, that's the 'copper tube' type of arrester I mentioned. I think that should be fine. You might not need it, but if you do, you'll be pizzed you didn't add it when you had the chance!
 
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Old 04-10-15, 06:54 AM
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Yes - you are right. The manual for the burner calls out one controller and looking at the one on the unit now, it's the L4081B10131 - I wonder if it was changed out?

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