Conventional Hot Water Tank Off of a Coal Boiler?

AH! Now I get what your doing. This is how my house was setup before - sorry for the confusion ...

What I had was this: 3 ways in to the tank. One on bottom with drain, one on top, one in middle. The top went out to HW faucets, middle went into one end of tankless coil, & the bottom, the other end. Then on one part of that loop to the tankless coil, there was a T, for fresh water to enter the system. Tank was hollow inside. There was a circulator that kicked on with a snap t-stat that was screwed to the tank. Circ would kick on if temp went below 115° ... then kick off above 127°

I'll see if I have any old pics I can dig up of that setup. It worked much better than the tankless alone.

I see now that an aquastat is just a thermostat for water. It would be the device that turns on the brass circulator pump when the tank goes below 115 degrees, and then turns off the circulator pump when the tank reaches 127 degrees. No zone valve required at all with this arrangement if I'm understanding correctly.

When you first wrote

lsayre wrote:the optional internal "tankless" hot water on demand coil from a coal boiler,

I took that statement to mean you had the coil in your boiler now and wanted to make use of it.

Confirm?

Actually I'm still looking at coal boilers, and I presently have an old oil boiler. The various coal boilers offer a "tankless hot water coil" as a low cost option, and I was wondering if I could justify this option by using it to heat my conventional electric hot water tank. I would rather have it set up to a tank than use it as a direct on demand hot water supply system.

akhemmmm

Wish you would have posted that tidbit in the first place

Run the domestic cold water supply to the coil in your coal boiler.
Feed the electric heater with the domestic HOT water FROM the boiler. ( input the hot water into the "cold" inlet "
If you want to circulate the water, run a loop from the drain to the cold water feed to the domestic coil inlet. This loop will
have a small brass or stainless pump, a thermostat, and a check valve. Put the thermostat bulb
down at the bottom of the loop coming from the drain.
For summer use, don't do anything except unplug the circulator.
When you use hot water, the flow goes first to the boiler, then to the electric hot water heater.
The loop just keeps the electric hot water heater tank up to temperature. The thermostat lets
you set the temperature of the tank.

The answer is yes, you can use the DHW coil in a coal fired boiler to heat your Electric hot water tank..

You can do the full and 'correct' system that Sting and tsb suggest or you can go the 'el cheapo' route that I and leward did..

I simply route the cold watet that normally enters the DHW heater through the coal heating device, THEN into the heater's tank..
Now this has a slight problem. the water in the heater won't stay hot UNLESS you are using hot water.. if the tank sits for say 12 hours with no DHW use, then the electric element will sense cool water and heat the water..
What I do is simply remember before I go to bed, to run 3-5 gallons of hot water, which 'charges' the heater/tank with HOT water and this then keeps the heater from running the heating element till my morning shower..

Sting's method will alway keep the tank at the proper temperature, but does require you to purchase and to install some additional hardware..

Both way's work, if you have a family that uses plenty of hot water during the day, then the 'el cheapo' method will work fine..

There is no doubt that you can get paid back for the purchas price of the DHW coil in a boiler within just a few months of use..

Greg L

Found my pics from '03 ...

After looking at these pics, it seems my memory isn't as good as I had thought. There was no "middle" connection. Looks like there were two bottoms, and a top. Hard to tell from the pic, but 2 bottoms were in the circulator loop for the tankless coil in the oil boiler.

Basically, fresh water connected straight to the bottom, with a T going into the coil. The other bottom connection went out to the other coil connection. The very top connection was the output to the faucet. That makes sense, as this is where the hottest water would stratify in the tank.

You can see the condition this system was in, & why I had to make the jump for an indirect ...

Gregs system is bullet proof

but it has the potential under large demand to run too hot - and that's dangerous

Consider that when the boiler is under load it could be producing Domestic hot water well above 120 max temp code says to deliver to taps -

Pink body parts do not heal well or fast enough - sometime not at all

a work around to ->This small issue <- (NOT) is to incorporate a non electric thermo limiting valve to protect the tap temperatures

my system uses one to supplement and hold temps ( because I limit the tank temperature) but I also recirculate and hot water is almost instant at the tap - no small benefit in my little place.

Perhaps the hot/cold water thermo mixing valve is a second level of safety that should be incorporated to prevent greater than about 120 degree water from ever having the chance to find the skin? If adding this device, where would it go in the system?

lsayre wrote:Perhaps the hot/cold water thermo mixing valve is a second level of safety that should be incorporated to prevent greater than about 120 degree water from ever having the chance to find the skin? If adding this device, where would it go in the system?

There are point of use (under the sink) or what I like, right at the tank. You can see it at the left side of the tank with the red knob. Blends the hot and cold together.

Sting is 100% right. I neglected to mention that my hot water tank is often at 160*+.. now, I don't have kids, and I really don't like bacteria growing in my hot water tank, so I like it this way..

But EVERYONE should install a good tempering valve in the supply line from their hot water tank to prevent scaulding or worse, serious burns..

It's funny, I use a tempering valve to control the temperature of the water in my hydronic floor, but don't for my hot water faucets..

By all means be safe and careful with hot water..

Greg L

To continue -- my "frugal" way -- I do have a tempering valve at my boiler that mixes the water feeding my electric hot water tank to about 120 degrees. What I like is that my electric bill goes DOWN once I fire my boiler. The electric rarely kicks on. I have a "demand" gizmo from my electric co-op, that cuts the power to the hot water tank when the load on the system rises. I get a $7 dollar credit from them for helping--for the most part they could shut it off all the time in the winter. It simply functions as a hot water storage vessel. I'm not sure why you would go to any great lengths, or a "fancier" system. My total cost was about $6 for a valve and a tee.

A syphon loop to/from the coil in the boiler to your tank may suit you. Mine is setup as such, the elec tank is shut off, and the syphon loop is heating the water. Recovery time is a bit long.

A pump and 'stat on the syphon loop would probably greatly improve recovery time. My Wife and I coordinate shower times to get around it.

See this thread for pics of the loop on mine. No pump. See Dec 9th posts.

Can I "T" Into My Hot Water Heater Drain Valve

Dave

Have any of you been able to successfully supply hot water to your household exclusively from a DHW coil, without the use a hot water tank (either direct or indirect)? If so, how did you accomplish it? How well is it working out for you?