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Old 08-30-2012, 04:04 PM   #1
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Electric vs Oil hot water


We moved into a new house in January, where we have a 1 year old Weil-McLain oil fired boiler which provides hot water for the baseboard heat, and hot water from the tap. Around Aug 1 we got an oil fill... 120 gallons... and I realized that the $470 oil bill was primarily for hot water, since our last fill was in April. We barely had the heat on in April. Based on our weather, we're not going to use the heat much until mid-October. At this rate, we will easily spend $600-700 just for hot water for 6 months, or $120/mo.

Our old house (in the same town) had gas heat/hot water/cooking, and our gas bill in the summer was around $50/mo. We don't use more hot water in the new house than we did in the old house, and we actually have a new HE washer and new dishwasher. Plus, we did a lot of cooking with the gas stove/oven.

There's no gas main in the area, so conversion isn't likely. However I'm wondering if it would be cost effective to switch hot water over to an electric hot water heater.

It seems an electric hot water heater would be more efficient than the oil fired boiler. The boiler is designed to heat a 2000 sqft house. It doesn't make sense to fire that thing up just to get a few gallons of hot water.

Would it make sense to convert to electric hot water heat?

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Old 08-30-2012, 06:10 PM   #2
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Electric vs Oil hot water


The best way to handle your hot water IMO would be to add an electric hot water heater and valve it in with the boiler (Summer/Winter hook up called around here). The boiler would make the hot water in the winter. This would be cost efficient as the boiler would be hot from heating the home. In the summer the water would be heated by the water heater. The boiler can be turned off in the summer and not have to maintain temp to heat hot water.


Only down side is most boilers will tend to have leaks occasionally when done this way. They are caused by the seasonal expansion and contraction of turning it on and off.

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Old 08-30-2012, 06:56 PM   #3
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Just install an electric water heater and forgetaboutit.

Make sure you valve off the hot water inlet and out let on your heater and shut your heater off on the off Season. Keep it simple and you will be way ahead of the game.

PS. Leave the piping and hot water connected to your heater in case of an emergency. And you might have to make changes on the boiler controls to take the water heater control out of operation.
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Old 08-30-2012, 07:04 PM   #4
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Electric vs Oil hot water


Install an electric water heater. Don't tie it into the boiler at all though. In the winter, if you would use the boiler for domestic hot water, it still raises your oil bill.
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Old 08-30-2012, 10:27 PM   #5
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Electric vs Oil hot water


Thanks for the replies. A winter/summer switch seems like a very good idea. I'll probably wait until the spring to have the electric heater installed.
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Old 08-30-2012, 10:48 PM   #6
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just install electric water heater...keep it seperate from boiler...
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Old 08-30-2012, 11:14 PM   #7
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YES- just install separate HW Heater..when you use the boiler for DHW you run the risk of excessive cold water through the heat exchanger which, in turn, can result in the boiler cracking due to high differential operating temps, i.e., during high use of hot water more cold water is introduced into the heat exchanger causing possible Thermal Shock to the boiler..Not worth the risk. Also, you are correct..absolutely does not make sense to keep boiler hot all summer just for hot water..AFUE, (annual fuel utilization efficiency) drops like a rock! $$$$
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Old 08-31-2012, 11:25 PM   #8
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Put an electric tank in series with your coil. That way you can turn what I'm assuming is a warm start boiler down to a lower temp. without shutting it off.(Shutting it down completely may turn its gaskets as leaky as a new puppy) It may cycle on when there is a heavy draw but nowhere near as often. And FWIW, all the cold water in the world won't crack your heat exchanger, IF its piped properly.
(If it is a cold start, then do what everyone has said and pipe a separate electric tank and shut it down in the summer)
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Last edited by Canucker; 08-31-2012 at 11:28 PM. Reason: More info
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Old 08-31-2012, 11:56 PM   #9
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As long as you don't drain your heating system and boiler the gaskets will be fine and will not leak. Heating boilers typically last 40 - 50 years and are left OFF `for many months when not required without a gasket leak.

I don't know how your system is piped or controlled so, that's why being cautious regarding introduction of cold water through heat exchanger.

Still doesn't change the fact that the mode of operation is very inefficient during summer but you could install electric heater in series with boiler as standby or extra back up during heavy demand but would increase standby losses during non heating (summer) mode.
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Old 09-01-2012, 02:25 AM   #10
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Quote:
Originally Posted by techpappy View Post
As long as you don't drain your heating system and boiler the gaskets will be fine and will not leak. Heating boilers typically last 40 - 50 years and are left OFF `for many months when not required without a gasket leak.
I will agree, when it comes to cold start, not warm start boilers.

I don't know how your system is piped or controlled so, that's why being cautious regarding introduction of cold water through heat exchanger.

Still doesn't change the fact that the mode of operation is very inefficient during summer but you could install electric heater in series with boiler as standby or extra back up during heavy demand but would increase standby losses during non heating (summer) mode.
Standby losses wouldn't be any more than they are now, as long as its piped properly. The bonus would be the ability to turn down the boiler aquastats to minimize its firing during summer.
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Old 09-01-2012, 08:00 AM   #11
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Simply by directing DHW via the heat exchanger you are adding to standby heat loss through that heat exchanger. i.e., there are heat losses through any additional heat exchangers in any system. Preheated water goes through secondary heat exchanger(s). All boilers/tanks/heat exchangers have some losses the rate of which depends on the difference between ambient temperature, water temp and insulation values of the particular heat exchanger so any additional heat exchanger adds to losses. Particularly with increased flow. AND..if you actually allow the boiler to start up, just for hot water your losses will skyrocket! Just think! Start cold boiler to add a few gallons of hot water. All the water in the boiler has to be heated and then all that water is cooled back down through vent losses. That is not efficient.

Last edited by techpappy; 09-01-2012 at 08:06 AM.
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Old 09-01-2012, 08:45 PM   #12
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Thanks for the lesson in heat exchangers. I agree with that assessment, if it's a cold start boiler to begin with. The OP hasn't said yet, but from the description in the first post, I'm willing to bet its a warm start. Do you understand the fundamental difference between a warm start and cold start boiler? I'm not going to advocate turning off a system that has maintained a set temp. since the day it was commissioned. Very good odds that the OP won't be a happy camper when they fire it up again. But, if you add the electric before the coil, then turn down the aquastats on the boiler, just think, it doesn't fire as often on demand, saving oil. Is it a perfect solution? Depends on the costs of electric vs. oil and their water use habits for the OP. They may find the cost of electricity rises enough to offset the savings they made on lower oil use
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Old 09-01-2012, 10:34 PM   #13
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If you install an electric water heater before the tankless coil of a boiler. You are effectively heating the boiler with the electric water heater.

A boiler with a tankless coil can have its aquastat set to 100 to prevent gasket leaks.
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Old 09-02-2012, 12:15 AM   #14
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From one Canuck to another..first of all no, I never heard of a cold start boiler as opposed to a warm start boiler. But, I will look into it. Most boilers are installed for heating only so, they cool off to room temp over the summer and heat back up when required for heat..so, 70 degrees over summer then fire up until 110 then the circ pump is activated forcing the system water back through the boiler until operating set point is reached..which could be up to 180 ..so, it is desirable to install an outdoor reset control which will vary the boiler temp depending on the out door temp ..the OD Control is adjustable so, it can be set on a curve depending on location e.g., the max temp can be higher or lower depending on whether you are located in NC or Alaska..This minimizes standby losses during OFF PEAK loads AND peak load only occurs 2% of the year in most locales Very well worth the cost. I have seen Weill McCLAIN boilers that have run this way for over 40 years without a problem except when a heat exchanger has been added!

Also..what's going on! Why aren't they installing HI EFF condensing type boilers? Much more efficient. I was converting heating boilers in commercial buildings, to condensing type, 30 years ago! Resulting in huge paybacks.

Last edited by techpappy; 09-02-2012 at 12:21 AM.
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Old 09-02-2012, 08:25 AM   #15
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Quote:
Originally Posted by beenthere View Post
If you install an electric water heater before the tankless coil of a boiler. You are effectively heating the boiler with the electric water heater.

A boiler with a tankless coil can have its aquastat set to 100 to prevent gasket leaks.
It sounds like the next time I run into it, I'm better off running the electric completely separate then cranking the aquastats down. Still seems like a lipstick on a pig solution but what can you do, eh?

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