Adding an electric hot water heater to my oil boiler for domestic hot water

NAmenta

Hello, so first I will say pardon my ignorance on this matter before I ask my queations.  Currently I have a 3-4 yo Utica oil boiler with baseboards for heat and hot water...tankless. I have noticed since we bought the house and moved in a couple weeks ago that we are burning through oil very fast, faster than at our 4 bedroom apartment which was pretty good size (it had an oil boiler and electric hot water heater and house was from the 1800s poorly insulated). 

We are about to start using wood to supplement heat and want to put an energy efficient electric hot water heater in so the boiler won't have to run as much. The theory is I will save on oil and go through a lot less than we are now.

What is the best way to add the electric water heater? I was thinking of piping it in to the water in and out of the boiler coil with bypass valves so the option to go back to oil heated water is always there if needed? Is this correct? If so what else will I need to do? Thanks and any help is greatly appreciated.

Nick

PC7060

Can you provide a picture of the current system?

Separating the two systems is pretty simple and should work as you described.  Pretty sure there was a similar thread with the last month or so but they removed the coil completely. . 

Not sure how advisable it is to keep the boiler DHW coils as failover option,

Jamie Hall

Before you decide to put in an electric water heater, be sure to compare energy costs in your area. You might find that a stand alone LP or oil fired water heater was much less expensive to run.

STEVEusaPA

Jamie Hall said:

Before you decide to put in an electric water heater, be sure to compare energy costs in your area. You might find that a stand alone LP or oil fired water heater was much less expensive to run.

Or an indirect. Unless you have very cheap electric rates, an indirect off the boiler is your best option.
Our long lost Wallie, @icesailor had posted a diagram of how to pipe an electric water heater (tank) off of a coil.

NAmenta

PC7060 said:

Can you provide a picture of the current system?

Separating the two systems is pretty simple and should work as you described.  Pretty sure there was a similar thread with the last month or so but they removed the coil completely. . 

Not sure how advisable it is to keep the boiler DHW coils as failover option,

Here are some pictures. Let me know if you need more. Out of curiosity why might it not be advisable to keep the DWH coils?

To respond to you Jamie, i still will be using this boiler to heat the home just not as much so to put an additional oil fired utility in seems kind of counterintuitive. I plan to get solar in the spring so that's one of the reasons I was thinking of this route.

pecmsg

NAmenta said:

The theory is I will save on oil and go through a lot less than we are now.



Nick

In Theory a Bee can't fly!

In the end you will wind up paying 2 or 3 times as much for electric then you did for oil. You need to find out why you're using that much oil. Oversized equipment comes 1st in my crystal ball, bad piping 2nd.

JohnNY

My preference in cases like this it to install an insulated storage tank fed by the coil and switch to cold start operation. Store your hot water for low-to-mid usage conditions and only fire the boiler when a longer, more-efficient cycle can be run to heat the stored water.
Electric water heaters make pretty good storage tanks so you might as well use one and wire it to run when/if the tank temperature drops to some value that suggests the coil may not be keeping up for whatever reason.
Stuff like this is fun and many people in my family have been willing guinea pigs to test my theories...with varying results.

NAmenta

JohnNY said:

My preference in cases like this it to install an insulated storage tank fed by the coil and switch to cold start operation. Store your hot water for low-to-mid usage conditions and only fire the boiler when a longer, more-efficient cycle can be run to heat the stored water. Electric water heaters make pretty good storage tanks so you might as well use one and wire it to run when/if the tank temperature drops to some value that suggests the coil may not be keeping up for whatever reason. Stuff like this is fun and many people in my family have been willing guinea pigs to test my theories...with varying results.

So basically you saying get the electric heater and use it primarily as a storage tank with the option to heat water if needed so I am not firing up the boiler to heat water as much?

As far as electricity, yes its expensive however I don't want to have to buy oil in June to have hot water. Also we will.most likely be getting solar in the spring so that will help with that. Plus the heater I was looking at is supposedly pretty energy efficient or so they say.

pecmsg

NAmenta said:

JohnNY said:

My preference in cases like this it to install an insulated storage tank fed by the coil and switch to cold start operation. Store your hot water for low-to-mid usage conditions and only fire the boiler when a longer, more-efficient cycle can be run to heat the stored water.
Electric water heaters make pretty good storage tanks so you might as well use one and wire it to run when/if the tank temperature drops to some value that suggests the coil may not be keeping up for whatever reason.
Stuff like this is fun and many people in my family have been willing guinea pigs to test my theories...with varying results.

So basically you saying get the electric heater and use it primarily as a storage tank with the option to heat water if needed so I am not firing up the boiler to heat water as much?

As far as electricity, yes its expensive however I don't want to have to buy oil in June to have hot water. Also we will.most likely be getting solar in the spring so that will help with that. Plus the heater I was looking at is supposedly pretty energy efficient or so they say.


Punch in the #'s and see for yourself.

https://coalpail.com/fuel-comparison-calculator-home-heating#:~:text=Fuel Comparison Calculator for Home Heating , $1,623.38 15 more rows

Oil in June is cheap!

NAmenta

pecmsg said:

Punch in the #'s and see for yourself. https://coalpail.com/fuel-comparison-calculator-home-heating#:~:text=Fuel Comparison Calculator for Home Heating , $1,623.38 15 more rows Oil in June is cheap!

So then what about what John mentioned and use the electric tank heater for storage and as a secondary means of heating water when and if needed?  Not sure I can punch the numbers in yet as we have onl closed on the house 2 weeks ago and don't have all the data yet for comparison.

STEVEusaPA

Well if you really want to get creative, visit:
https://idronics.caleffi.com/

Put a solar storage tank in the house. Let the boiler charge the tank when needed for domestic hot water, or even better, get a storage tank with 2 coils, use it as a buffer, run the zones off of it, and use if for domestic. Then the boiler runs only to charge the tank, and the solar panels will cut down on the oil usage.

But back to my first comment, and indirect will save you the most money on oil. With or without no one home, my boiler runs for 2 or 3 (4 at the most) up to 10 minute cycles in the summer for domestic. Even if it ran for an hour, that's only 3/4 gallon per day. If I had solar storage, I doubt the boiler would fire at all on sunny days.

pecmsg

I ran rough #'s
#2 Oil $3.50 per gal 80% eff $3,154.
Elec $0.25 per KW $7,327

NAmenta

Thanks guys....so roughly how much is an indirect HWH? More than a direct electric heater?  I would like to get this done soon due to rising prices and supply issues but am trying to do this as cheaply as possible due to Christmas being right around the corner.

HVACNUT

We don't discuss prices here so get some estimates. 
But as far as adding a storage tank to your existing system, this is typical. This example is from John Wood. Still need to maintain a minimum boiler temperature though. 

Larry Weingarten

Hi, I might want to look into heat pump water heaters and race that technology against the others, though I’d put it ahead of the boiler so it is always fed the coldest water.

Yours, Larry

pecmsg

NAmenta said:

Thanks guys....so roughly how much is an indirect HWH? More than a direct electric heater?  I would like to get this done soon due to rising prices and supply issues but am trying to do this as cheaply as possible due to Christmas being right around the corner.

Going Cheap has little if any return on investment!

NAmenta

HVACNUT said:

We don't discuss prices here so get some estimates. 
But as far as adding a storage tank to your existing system, this is typical. This example is from John Wood. Still need to maintain a minimum boiler temperature though. 

Thank you and understood. So the above diagram would work for an electric direct heater used as a storage tank or for just a stand alone tank only? Also my current setup has an expansion tank if you can see in the pictures I posted. Does the diagram mean I would add another expansion tank or would I be covered with the one I have currently installed?
Thanks!

NAmenta

Pecsmsg...I should have worded different. Not cheaply as possible but as cheaply as possible without using crap and still doing it the right way.

pecmsg

Can you post some pictures of your current set up? Boiler make and model. Near piping from a distance.

STEVEusaPA

Yes a proper expansion tank for domestic water would be a good idea. You probably don't have to maintain temperature in the boiler but you do have to protect it from sustained cool water return temperatures on the boiler side. You could change the aquastat to a Hydrostat 3250+, set it up for cold start, and use the well/aquastat in the storage tank to trigger a zone call from the ZR ZC terminals.

In the above drawing, make sure your circulator is stainless steel or bronze.
Personally if I were doing all of that I would just get an indirect and pipe it as it's own zone. A small indirect is probably 2, to 2.5 times the cost of a simple electric water heater.

Hot_water_fan

A heat pump water heater is what you want for efficiency, especially if using solar. Forget all the complication and  leave it separate from the oil boiler. There’s no reason to do the indirect. 

EBEBRATT-Ed

My vote is for a storage tank with 2 coils. Ditch the tankless heater and pipe 1 coil off the boiler just like any indirect. Use the other coil to heat with your solar install. Buy a big tank

NAmenta

So Steve....then a second expansion tank you mean? I have one currently on the boiler. You can see it in the pictures.

STEVEusaPA

NAmenta said:

So Steve....then a second expansion tank you mean? I have one currently on the boiler. You can see it in the pictures.

The tank pictured is the expansion tank for the boiler side of the system. It should have a charge in it that matches the boiler's cold fill operating pressure-usually around 12 psi. It's main function is for the water to have a place to go as the temperature increases and the water expands in the close system.

The second tank looks the same, but is one designed for potable water. It goes on the cold pipe on the domestic side of the system, before the tank. It's charge will be at least 60 psi. It's main function is to prevent street pressure from causing the relief valve on the storage tank to trip. This could happen for a number of reasons, but usually occurs when something happens like rapid opening then closing of any valve or spigot on the domestic side-washer machines, dishwashers, sprinklers, or just high incoming water pressure and someone shutting off a spigot that's running full tilt.

NAmenta

Ok so I'm not sure if this will be an issue but here is a picture of the HWH I was going to buy. Going off thr diagram posted the hot water would go from the coil to the drain of the HWH. The drain appears to be some sort of synthetic material and not brass. Will that withstand the temp of the water coming from the coil?

JakeCK

Like @Hot_water_fan and @Larry Weingarten have said, look into a heat pump water heater.

I installed one a month ago. It has been doing good. My only issue is still tweaking the schedule to optimize energy usage. You said you plan on getting solar? I had pv panels installed this summer and I have the tank programmed to produce hot water during the day while the sun is shining. Although the wife likes to wash a half dozen load of laundry in the PM so I've had to adjust the schedule. I like to have hot water when I get home in the am...

Still trying to tra... convince her to do laundry on the weekend during the am. lol

NAmenta

Yeah that will be an issue for me too. My wife does a ton of laundry at night. I am hoping to get solar. I should be able to but I still need to have them come out and make sure it's worth doing in regards to the location of my house and the sun it gets and the trees I have in my back yard. I should be ok but I am not 100% yet.

hot_rod

Solar PV or thermal? If PV then a heat pump water heater

www.dsireusa.org. Check for rebates on HPWH

Hot_water_fan

Solar PV or thermal? 

Ha, at this point it’s 99.9% likely to be PV!

EBEBRATT-Ed

@NAmenta

you can take the plastic valve out and pipe into that port with copper or brass. Then put on a tee with a brass drain valve on it

Robert_25

NAmenta said:

Hello, so first I will say pardon my ignorance on this matter before I ask my queations.  Currently I have a 3-4 yo Utica oil boiler with baseboards for heat and hot water...tankless. I have noticed since we bought the house and moved in a couple weeks ago that we are burning through oil very fast, faster than at our 4 bedroom apartment which was pretty good size (it had an oil boiler and electric hot water heater and house was from the 1800s poorly insulated). 

We are about to start using wood to supplement heat and want to put an energy efficient electric hot water heater in so the boiler won't have to run as much. The theory is I will save on oil and go through a lot less than we are now.

What is the best way to add the electric water heater? I was thinking of piping it in to the water in and out of the boiler coil with bypass valves so the option to go back to oil heated water is always there if needed? Is this correct? If so what else will I need to do? Thanks and any help is greatly appreciated.

Nick

You are assuming that the reason for your higher than expected oil consumption is the tankless coil. That may or may not be the case. Has the oil boiler been serviced? If not I would start there.

Based on the pictures, you have an older home. It may take a lot more to heat it than you expected. Before spending money on a solar system, I suggest having an energy audit done on the house and see where all of your heat is going. Tightening up the house will likely have a much faster ROI than the solar.

If installing a wood stove make sure you are mindful of clearance to combustibles, and get a good stove - the newer EPA models are much more efficient than the models we grew up with.

NAmenta

To answer a couple of you....yes its an older house, its an expanded cape built in 1942 so I'm sure jt doesn't have great insulation however the windows are newer. I am going to have an energy audit done soon actually, however feel I would benefit from a storage tank because of the amount of laundry my wife does alone with 3 kids.  The boiler was recently serviced.

I actually am just going to be using the fireplace for now until I can afford an insert so it will not be super efficient for the time being. Having a chimney and fireplace inspection done today.

As far as the solar goes I am waiting for the company to come and give me my options if any but it won't be thermal.

STEVEusaPA

So you want to save money on oil, and you're going to burn wood in a regular fireplace. The least efficient and least comfortable way to heat your home. All the heat will be drawn up and out the chimney, replaced with outside, cold air leaking into your home.

NAmenta

Like I said I plan to get an insert but I need to wait until after the holidays unfortunately. 

Jamie Hall

Doing a heat loss on your house isn't hard. You can do it yourself. I like this program: https://www.slantfin.com/slantfin-heat-loss-calculator/ but there are others. It really should be the first thing you do, and it will be much more helpful than the energy audit -- although there's no harm to an energy audit either.

It's a useful reality check. Keep in mind that you will need more heat in your cape than in your apartment, as the apartment probably had at least one or two shared walls and possibly a shared ceiling or floor -- all of which make quite a difference.

You might also be able to get some idea as to oil consumption from the previous owners, if they are feeling cooperative and are available.

I would advise against an electric water heater, if you can avoid it, unless you live in an area with very low electricity rates. The most efficient overall approach would be to add an indirect water heater fired by your boiler to replace the tankless coil -- it still uses the boiler, yes, but in a much more efficient way.

EdTheHeaterMan

It is tough to compare one building to another when looking at square feet to gallons used. The boiler efficiency, the insulation, common walls of apartment that have no heat loss, to the design of the control system of the boiler. just to name a few.

If your apartment has 1/2 of the walls ceilings or floors connected to a neighbor that is also heating their apartment, then you are not losing heat to the outdoors on those surfaces. With your single home, you are losing heat to all the ceilings that have a roof over them, All the exterior walls,, North South East and West. Any part of the basement walls that are above grade are also losing heat to the cold outdoors.

By using a tankless coil in a boiler that maintains a 160° operating temperature and is connected to a chimney. That chimney is a huge vacuum cleaner that is sucking lots of heat outside, along with the unwanted fumes from combustion. The hot boiler loses heat at a faster rate than a cold start boiler system would.

Now, when you make the change to a seperate tank, or to an indirect, or (as @HVACNUT suggested) using a water heater as the indirect and the tankless coil as the heat exchanger, You MUST rewire the oil boiler control to be a cold start boiler. Many plumbing contractors don't realise that is the major part of the ENERGY SAVING project. Getting the boiler to be a cold start.

Another thing that will happen is the gasket on the tankless coil has probably shrunk over time. Since the boiler is fairly new, you will want to snug up on the flange bolts to prevent the gasket from leaking. The gasket will shrink even more once the boiler is converted to a cold start. CARE MUST BE TAKEN WHEN TIGHTENING THE FLANGE BOLTS SO NOT TO BREAK THEM OFF. Ask me how I know? If you don't address the flange gasket now, you will not be able to later when the rust starts to build up around that coil flange

Finally, if you go with the water heater as an indirect, you will want to have someone design a control wiring system that will give priority to the loser cost energy source which may be the heat pump on the water heater, or it may be the oil boiler, I'm no sure on that point. But if you choose the lower cost electric water heater, you will probably want Oil as your primary heating source.

I wish you luck with your project

NAmenta

Thank you for your detailed response Ed. It definitely helped a lot and everyone else who gave their input too. Yeah my last place was the bottom floor of a 2 family built in the 1800s. Only shared ceiling but the place had terrible to no insulation and very drafty doors and windows.

So a couple dumb queations....can you explain cold start to me (pardon my ignorance on this) and is there a way to slow or cut down the heat loss from my chimney without killing us with carbon monoxide?

Thank you again!
Nick

Jamie Hall

In a cold start arrangement, the aquastat turns on the boiler when heat is called for from outside -- such as from the indirect -- rather than keeping the boiler at some warm temperature.

There are powered vent dampers available which are arranged to open on a call for the burner to fire. A good technician should be able to install one for you. They do save some energy...

NAmenta

Jamie Hall said:

In a cold start arrangement, the aquastat turns on the boiler when heat is called for from outside -- such as from the indirect -- rather than keeping the boiler at some warm temperature. There are powered vent dampers available which are arranged to open on a call for the burner to fire. A good technician should be able to install one for you. They do save some energy...

Thank you for the response and info!

EdTheHeaterMan

MikeAmann said:

Ed, not to hijack, but what type of gasket material works best for tankless coils?

Red rubber gasket material, if you plan or making your own. It is available at most supply houses for Plumbing or Automotive... but there are manufactured gaskets precut to the size of the flange for just about any tankless coil.

EdTheHeaterMan

NAmenta said:

Thank you for your detailed response Ed. It definitely helped a lot and everyone else who gave their input too. Yeah my last place was the bottom floor of a 2 family built in the 1800s. Only shared ceiling but the place had terrible to no insulation and very drafty doors and windows.

So a couple dumb queations....can you explain cold start to me (pardon my ignorance on this) and is there a way to slow or cut down the heat loss from my chimney without killing us with carbon monoxide?

Thank you again!
Nick

I think @Jamie Hall answered your query about the cold start and slowing down the heat loss up the chimney. i just want to further explain... You have a boiler that maintains a water temperature all the time. maybe about 160°. This minimum temperature is there 24/7 so if you want to take a shower at 2:00AM your cold water will flow thru the tankless coil in your Hot Boiler and come out at a reasonably warm temperature so you don't get a cold shower.

If you can store say 30 or 40 gallons of hot water in a well insulated tank, then your heating boiler that is connected to the chimney can turn off if there is no call for heat and the tank is full of stored hot water (that is not connected to the chimney vent). In the summer, when you don't use any oil for space heating, the boiler can get cold and less heat will be vented up the chimney. this results in less wasted heat up the chimney. We refer to that wasted heat "Down Time Loss". Cold start boilers have a much lower Down Time Loss when compared to a boiler that maintains a minimum temperature higher than the ambient room temperature.

Mr. Ed