Piping a DHW Coil Into a Electric Hot Water Heater

Lightning wrote:What about an arrangement like this? No extra pumps needed, electric tank powered off while the boiler is running. Natural convection heats the tank. Temperature recovery of the tank with the boiler would be pretty fast I'm thinking.

Have a valve between the drain on the tank and the input of the DHW coil to stop flow during the off season (like Rob suggested) and power on the electric tank. This valve would be needed so that the electric tank didn't try to heat the boiler during the off season.

I wonder how much more electricity would be used if you left the valves open to the boiler keeping it warm, that would help with condensation in the summer time wouldn't it if the water was warm. The DHW coil would be doing the opposite of its original job.

McGiever wrote:For anyone who is following along,
Just to be clear...the DHW through a coil is not a boiler zone. This DHW water is moved only by house water pressure upon manually opening a faucet or starting a hot water using appliance.
An automatic dump zone generally needs to activate a boiler zone.

Ok so if a person has a DHW coil in there boiler like mine, do I need a tank? Or just send my water through it bypassing the electric tank, making it like a "on demand" system?

hotblast1357 wrote:Ok so if a person has a DHW coil in there boiler like mine, do I need a tank? Or just send my water through it bypassing the electric tank, making it like a "on demand" system?

I've been using mine as an on demand hot water system year round for nearly 5 years now (and the valves have been closed off to my HWT, which has had its breaker off for all of this time) . Works fine most of the time (and for sure all summer it is fine) but on occasion in the winter you will take a mildly warm to tepid shower if you get the timing wrong and a zone (or worse, multiple zones) is (are) calling for heat right while you are in the shower, and the boiler hasn't fired and woken up yet. In the winter we have learned that it's best to shower right after the boiler has finished a firing cycle. Little chance for a disappointing shower if you discover and then obey a few simple rules.

Ok good too know, hence the reason there called tankless coils?

After 5 years of non-use, I'm contemplating of removing my HWT altogether.

Flyer5 wrote:

Rob R. wrote:
Make sure you can bypass the coil...you do not want to be running cold water through it when the boiler is not in use.

Just curious. Why? ( Scratching my head)

Running cold water through the coil cools the boiler down also, and in a humid environment it causes condensation on the boiler surfaces. Condensation + fly ash = not good.

great advice...I didn't consider the thermosiphon option....interesting. I think at first I am going to rig up the lsayers suggestion with some extra tees and ball valves so I can isolate the electric hot water heater or the coil. That way I an use the system as an all electric, on demand through the coil only, or preheat the water entering the electric.

thanks again

coldinmaine wrote:I didn't consider the thermosiphon option....interesting.

That diagram is how my DHW temper tank is plumbed and it has worked great for 3 heating seasons now.. The difference being that my DHW coil is in the fire box of my hand fed furnace instead of being submerged in the boiler water like yours would be.

hotblast1357 wrote:I wonder how much more electricity would be used if you left the valves open to the boiler keeping it warm, that would help with condensation in the summer time wouldn't it if the water was warm. The DHW coil would be doing the opposite of its original job.

Right, I'm betting it would use a lot more power than running a 100 watt light bulb, unfortunately.

"hotblast1357 wrote:
I wonder how much more electricity would be used if you left the valves open to the boiler keeping it warm, that would help with condensation in the summer time wouldn't it if the water was warm. The DHW coil would be doing the opposite of its original job.

Right, I'm betting it would use a lot more power than running a 100 watt light bulb, unfortunately."

It could be....I have a hybrid (heat pump) hot water heater and It uses minimal power to maintain temp....it also a 40 amp element for high demand. We have pretty high demand so coal is cheaper.. and running the boiler 365 will protect it from rust....so I plan on running the boiler over the summer.

Fwiw;

I have side arm type heater on the boiler piping mains that preheat the water going to the DHW tank, I also have a gravity [syphon] loop from the boiler's coil to the tank, just like Lightning's May 19 post picture. I had a small brass pump on said loop, but it was more bother than it was worth and I eliminated it. This may not apply to you, as my DHW tank is only 4' from my boiler, which allows the syphon loop to work very well. DHW tank is switched off and two long showers back to back are not a problem.

2 cents worth on controls;

DHW use would often catch my little Kaa-2 off guard and pull too much heat from it. I now have my boiler set up to run the stoker when hot water is drawn. It made a HUGE improvement.

I use an aquastat placed where the piping stays hot when no water is being drawn. It is wired to the TT terminals on the triple stat on the boiler. When water is drawn, incoming water cools the pipe, which causes the 'stat to close and the stoker runs. When the water flow is stopped, it takes 5 or so minutes for the piping to heat back up, opening the stat. If it happens that the boiler is above high set point, the triple stat in the boiler prevents the stoker from running, as it would with a call from another device [zone valve, etc]

Dave

2 pics of syphon loop. Pre-heat system in next post.

Put fire in boiler: close one valve, open two on "side-arm" system. Open valves on syphon loop. Syphon loop valves are closed with no fire. If I forget, elec DHW tank will heat boiler to 100* or more! Valves and spigot placed to allow flushing boiler's coil.


Other pics are "sidearm" pre-heaters. Well water goes to return side side-arm first, crosses to supply side side-arm, them down to tank. Spigot on side arm cross over pipe allows flushing.

Note the "fire in boiler" piping takes water into the bottom of tank. Some water may be forced through the boiler's coil and to top of tank. I'm not sure.

You can see the aquastat that calls to the boiler when water is drawn. Incoming well water quickly cools it when water is drawn.

Valves allow normal water in path with no fire in boiler.

Dave

"side-arm" style pre-heaters. Made by grinding stops out of 1.5" x 2" x 3/4" tees and running the 1 & 1/2" through the 2".

My boiler is simply plumbed before the electric water heater. 2 guys at work have it this way for over 30 years on EFM 520s and I see no reason why you would want it any other way. You put a valve between the inlet and outlet on the boiler, crack it open you don't send cold water into the boiler, avoiding shock as I was told. My water heater never comes on as far as I know and I have basically endless hot water, it gets hotter as you use it! My electric bill was $56 last month. I have ball valves so if either system leaks I can bypass them. No pumps needed.

I had one of these on the syphon loop.

Some dummy forgot to open the loop valves when he put a fire in the boiler. The water in the loop/coil expanded and split the brass casting. It is not really needed with a short syphon loop, so I eliminated it.

http://www.watts.com/pages/_products_details.asp?pid=6677