Converting Oil Boiler to Electric Water Heater


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Old 05-11-10, 04:00 PM
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Converting Oil Boiler to Electric Water Heater

Hi All,

I have a furnace that also provides Hot water via the Hot water Coil. The unit is ~ 15 years old. I have never had good hot water in this house ( It is a country house which I now rent)
I want to convert to a 50g electric Water heater( as an Indirect option is too expensive). My existing coils in the furnace are bad and would have to be replaced anyway. So what is the best way to connect to the Electric unit

1) have water continue to run thru. the Furnace than to the Electric water heater. If i go this way, do I will keep the unit on all year round and have it cycle to some low level ( like 120 degrees) to keep the furnace from going dormant which someone said is better than shutting it down during the summer. The 120 dgrees would be fed to the electric which could than supplement the heat or maybe a lower temperature? The existing coils are starting to fail and will eventually stop working . In which case the water would just pass thru. the furnace to the electric once they fail?
2) Cap off the boiler in the furnace. Shut it down in the summer and run completely off the electric

Thanks in advance
 
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Old 05-11-10, 04:20 PM
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Originally Posted by Turt62 View Post
2) Cap off the boiler in the furnace. Shut it down in the summer and run completely off the electric
I assume you have oil-fired, hot-water heat.

Of the two choices, No. 2 would be mine.

But if you're renting, I'm not sure it is wise to be making any such modifications to the system. This should be your landlord's problem. What if you tear into the system, and encounter a big problem? Are you planning to pay for the electric water heater? Also, is your electric service OK for adding an electric water heater?

Running your boiler at 120 deg in the summer (or any time) could be damaging due to condensation in the boiler or flue.

If your boiler's hot water coil is bad, how could you implement option No. 1? When you say the coil is bad, what do you mean? They leak? Or what?
 
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Old 05-11-10, 06:44 PM
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I might keep the coil to only preheat the water if and when the boiler is on due to a call for heat.
I don't think I would run the boiler all summer just for DHW preheat.
120 is too low as Mike stated, you will have flue gas condensation and bigger problems in the fall.

Simplest is either a oil fired DHW tank or electric.

From a price standpoint, electric makes all the sense in the world.
 
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Old 05-12-10, 07:47 AM
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Originally Posted by TOHeating View Post
I might keep the coil to only preheat the water if and when the boiler is on due to a call for heat.
I don't think I would run the boiler all summer just for DHW preheat.
120 is too low as Mike stated, you will have flue gas condensation and bigger problems in the fall.

Simplest is either a oil fired DHW tank or electric.

From a price standpoint, electric makes all the sense in the world.
Electricity being cheaper really depends on where you live, I can tell you anything electric in my area can pretty much be thrown in the garbage because of cost to operate. Easy one year payback if replaced with an oil fired water heater. You also need to remember that electric hot water tanks will usually have really slow recovery times.
 
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Old 05-12-10, 02:08 PM
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Originally Posted by Spider-One View Post
Electricity being cheaper really depends on where you live, I can tell you anything electric in my area can pretty much be thrown in the garbage because of cost to operate. Easy one year payback if replaced with an oil fired water heater. You also need to remember that electric hot water tanks will usually have really slow recovery times.
Where are you being [buying?] electricity ?
In ontario it's not that bad, oil on the other hand is crazy.
The price of an oil fired DHW tank installed has to be a few grand. The cost of an electric tank is a couple hundred.
Sure the oil will recover faster, but it's costs for to run.

Dollar for dollar for DHW I don't think electric is all the silly. For heating, well lets not go there.
Unless it's driving a geothermal heat pump compressor.
 

Last edited by NJT; 05-13-10 at 03:57 PM. Reason: buying?
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Old 05-12-10, 03:45 PM
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I live in the NWT where power is ridiculous. Obviously not everywhere will be the same but my main point was it's really dependant on where he lives and his cost for power/oil and that there can be benefits to oil DHW like recovery time. I know for people around here electric hot water can pretty easily add $150-$200 to the monthly electric bill with normal usage.
 
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Old 05-12-10, 03:46 PM
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I might keep the coil to only preheat the water if and when the boiler is on due to a call for heat.
What happens if the coil gets 'limed up' and ya can't get nuthin but a weak pee stream out of it?

If you do abandon the coil in the boiler, don't cap it. Manufacturers recommend leaving the coil open so pressure don't build inside it. If you wanna cap it, drill a small hole in one of the caps.
 
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Old 05-12-10, 07:51 PM
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I would run all the cold water thru it, or a good portion so lime build up would not be an issue.
Still not likely a great idea :-)
 
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Old 05-13-10, 08:12 AM
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Thx Mike

I am the Landlord and I have renters

There is no leak in the boiler. It is just a performance issue( Hot water supply is low) and if I were to keep the system as is I would have to get a new coil & mixing valve( $800 installed per the Oil guy). Sounds like I should just abandon the current setup Cap it off and install the Electric. Is my Oil guy giving me a line by saying that the life of my furnace will suffer if I shut it down for the summer?
 
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Old 05-13-10, 09:53 AM
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Originally Posted by Turt62 View Post
Is my Oil guy giving me a line by saying that the life of my furnace will suffer if I shut it down for the summer?
I don't think it will suffer. I can't think of a reason why it would. It would be interesting to learn his reasoning.
 
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Old 05-13-10, 01:02 PM
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Mike,

He trying to say that by having the unit sit idle, the mechanisms can suffer. Whereby if you keep it running all year round, it keeps everything lubed etc.
 
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Old 05-13-10, 03:56 PM
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Two possibilites that I can think of...

1. The newer wet rotor circulators have a tendency to 'stick' when they are left idle over the summer. This is why some of them have a little plastic cap on the motor end. Remove the cap to reveal the end of the motor shaft with a screwdriver slot in it. If the thing does stick, takes about 5 minutes to 'unstick' it. Then once the pump runs on a regular basis, it's fine. Many of the modern boiler controls have circuits in them to 'excercise' the pumps for like 30 seconds, every couple days for this reason.

2. Some boilers, particularly the ones that use gaskets or O-rings between the sections instead of metal 'push nipples', that have spent their lives as warm start boilers have a tendency to 'weep' when they are allowed to go cold. The iron contracts and small weepy leaks develop.

But other than that, I can't think of a reason not to go cold start.

Again, just to make sure you noticed this:

If you do abandon the coil in the boiler, don't cap it. Manufacturers recommend leaving the coil open so pressure don't build inside it. If you wanna cap it, drill a small hole in one of the caps.
You could also just push the caps on the pipes and not solder them.

What make/model boiler do you have?
 
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Old 05-13-10, 04:51 PM
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Here in the U.S. Midwest, with gas-fired boilers and separate gas-fired hot-water heaters, boilers are shut down in the summer. (What else are you going to do with them? Keep them hot for no reason?)

Our circulators sit idle during the summer. And if non-pin-type boilers weep a bit in the summer, I'm not sure that is too serious.

I shut off my gas-fired boiler (and the pilot) during the summer. No problem yet.
 
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Old 05-13-10, 08:49 PM
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I shut my personal system down every year too... ONCE I had a problem where I had to 'kick start' the circulator in the spring... other than that, no problem... and I buy lots of beer with the money I save not running the thing all year long... I should probably say that it's going on 26 years old now.
 
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Old 05-17-10, 05:33 AM
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All this is good info....now for my two cents.
A boiler that is running hot for many years may weep a bit from the gaskets as NJ stated, especially the coil plate gasket which can be replaced if required.
As far as capping the coil also as NJ stated is not a good idea.
The setting to keep the boiler warm of 120║ is not a bad idea if you experience some weeping. It is not going to condense with a low setting of 120║ and a high limit of something above 160║. The boiler will not condense over the summer as you are not moving water through it. The water is sitting still and therefore will heat very quickly. I would even try going lower if you see Wheeling when turned off.
The thought is keep it warmer than room temperature. I realize the lowest setting is 120║ but the pointer does go lower.
I would also prefer cold start if possible.
 
 

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