DHW Hook up

My coal stoves has a coil that is hooked up to my hot water tank. It's hooked up according to Keystoker's instructions.
(Cold supply from the bottom drain outlet of the tank to the stove, hot supply from the stove to the pressure relief inlet on top of tank.) This works fine when there is no demand. Once someone showers, the water doesn't have a chance to warm up in the stove, then dumping cold water in the top section of the tank.
My question: can I hook up the return from the stove to the cold water supply of the hot water tank, instead of the pressure relief inlet? This way the water circulates to the bottom rather than the top? Maybe add a check valve or mixing valve on the cold water line?

Putting HW into bottom will dilute the heat...no HW till whole tank get's hot.

McGiever wrote:Putting HW into bottom will dilute the heat...no HW till whole tank get's hot.

When cold water is supplied at the bottom of the tank, doesn't that also dilute the heat?
I thought warm water mixed with cold water on the bottom is better (it will take less time for the electric heater to reach set point) than having the warm water dumped on top of the hot water, lowering the temperature going to the fixtures?
Forgot to mention, the hot water tank is electric and is always on.

Would this work? No circulator required.

lsayre wrote:Would this work? No circulator required.

Hey! I like this!
The only issue: This is only good when in demand.
When not in use, the electric heater is taking all the load to heat the water.
What happens to the water in the coil when not in use during high burn? (no circulation).

mariohotshot wrote:What happens to the water in the coil when not in use during high burn? (no circulation).

Oops, stupid me! I thought you had a Keystoker boiler. Do not heed my advice for a furnace or a stove. Sorry about that.

mariohotshot wrote:

McGiever wrote:Putting HW into bottom will dilute the heat...no HW till whole tank get's hot.

When cold water is supplied at the bottom of the tank, doesn't that also dilute the heat?
I thought warm water mixed with cold water on the bottom is better (it will take less time for the electric heater to reach set point) than having the warm water dumped on top of the hot water, lowering the temperature going to the fixtures?
Forgot to mention, the hot water tank is electric and is always on.

I cannot say it doesn't dilute to a certain degree...but here's the big difference...Water, just as any other fluid, including air, does stratify. As in that the warmer fluid is less dense and rises to the top while the colder fluid is more dense and will sink to the lowest point. All the fluid in between these extremes will stratify at the buoyancy level of it's density level.
So, you see, adding the cold water at bottom shall do the least to disrupt this natural stratification process.

What I often suggest for these applications is to unhook the lower electric element and let the upper element do the quick recovery only. You make room for the coal heated water while making sure nobody gets a cold shower, and use a whole lot less electric...that's what this is all about, right?

With the lower element always on you harvest very little coal heated water.

mariohotshot wrote:Forgot to mention, the hot water tank is electric and is always on.

You are only saving at most about 5% of your electric with this arrangement. And the circulating pump is probably using all or more of that 5 % savings..

lsayre wrote:Would this work? No circulator required.

No.. I don't see that plan effective at all...

Sorry, I noticed you commented later about it not being a boiler..

How many gallon is your WH? Are you saying you're running out of hot water after a shower, even with the elec. WH still on or are you just concerned about dumping cold water into your tank? Have you tried turning off the elec. to the WH and seeing how that works? A tempering tank could also work. I used to have one mounted directly above the stove and removed it like a dummy!

A stove/coil combination is all about storage and managing HW usage...slow recovery. I use my 50 gal. Elec. HW tank for storage only once the heating season begins. I've used this setup for our family of 4 (2 teens). Had to be careful back then not to use too much HW at once, but it worked. Now that there are just 2 of us and I can't remember a time we ran out of hot water. At this time of year I use a 6' hydronic baseboard to dump extra heat out of the system. We do things like running the dishwasher or showering before bed to allow the system plenty of time to recover. If the elec. needs to be on, I like McGiever's idea of turning the lower element off.

[/quote]You are only saving at most about 5% of your electric with this arrangement. And the circulating pump is probably using all or more of that 5 % savings.. [/quote]
My coal stove heats the water at an average of 140 degrees. The HWT is set at 120, so it only kicks on when the stove idles.
What about an aquastat? Will that work for me?

mariohotshot wrote:My coal stove heats the water at an average of 140 degrees. The HWT is set at 120, so it only kicks on when the stove idles.

I understand. But the problem with having the electric tank on in this situation (without a temper tank) is the recovery time involved. Lets say there is a small time frame of high demand, for example you take a shower, the wife takes a shower and a load of laundry is running and/or the dishwasher is on. A lot of cold water is dumped into the electric tank. Since the heating element is set to come on, it does and all that cold water that was just dumped in is heated by the electric element in a matter of 30 minutes and it shuts off.

The coil on the other hand needs a long time to recover, more like 12 hours. So you can see here that the electric element in the tank is doing a majority of the work load to heat the water. In the meantime the coil is just keeping it up to temp which doesn't take very much.

After further thought though, Since the coil is heating the tank to 140, you do have a little head room before the electric tank engages at 120. But even so, it's not saving you as much as you would hope. The real test would be to kill power to the electric tank and see if it will keep up on just the coil heating the water.

As far as the circulator is concerned, yer right, its dumping cold water into the top of the tank. My thinking is that if you just let it stratify naturally by using the thermo siphon method (no pump), hotter water will collect at the top of the tank AND also be the first to use, which I would think is the situation that you are looking for.

Are you able to measure the temp of the water entering and exiting the coil and what are those temps?

Lightning wrote:I understand. But the problem with having the electric tank on in this situation (without a temper tank) is the recovery time involved. Lets say there is a small time frame of high demand, for example you take a shower, the wife takes a shower and a load of laundry is running and/or the dishwasher is on. A lot of cold water is dumped into the electric tank. Since the heating element is set to come on, it does and all that cold water that was just dumped in is heated by the electric element in a matter of 30 minutes and it shuts off.

The coil on the other hand needs a long time to recover, more like 12 hours. So you can see here that the electric element in the tank is doing a majority of the work load to heat the water. In the meantime the coil is just keeping it up to temp which doesn't take very much.

After further thought though, Since the coil is heating the tank to 140, you do have a little head room before the electric tank engages at 120. But even so, it's not saving you as much as you would hope. The real test would be to kill power to the electric tank and see if it will keep up on just the coil heating the water.

I've been thinking about this post and discovered it is not accurate and I'm sorry..
My statement about it only saving 5% electric would also follow suit..

It breaks the rules as to "where are the BTUs going?".. The coil is constantly delivering BTUs to the tank, even after the electric element heats the water to 120 degrees. The coil will continue to heat the water and storing BTUs in the tank. Those stored BTUs will heat the cold water entering the tank when hot water is used. The electric element won't kick on again till the water in the tank falls under 120.

So basically you might have an issue of the water getting too hot if DHW demand is low or non existent for a period of time.

You guys didn't see my flaw?

As for the circulation pump, I still think the thermo siphon method would help.

There are 2 electric elements in the DHW tank.
Just unhook the bottom/lower electric element and life will be good.

Now no electric is ever used until the upper electric element gets switched on only after upper level water goes below 120*F set point. Remember: Stratification!

BTW: The very best thermo-sphion systems have shorter and larger diameter pipes with sloping pipes with the minimum amount of bends or turns.