Circulating hot water into thermal mass barrels

This may be a dumb question, but does anyone have thoughts on using drums or totes of water and circulating hot water to keep them warm on cold nights. They can collect sun during the day then use a small woodburner and some copper tubing to circulate some hot water into the night to get me through until morning. Is this worth the effort or a waste of time and energy.

FWIW
If your heat source is at least 2 feet below your storage bins than a thermosyphon loop can be set up without pumps.
just link all storage in series (on the bottom of the tank) and pull your cold from the bottom at one end and push the heated water into the top of the opposite end of your tank series.
Ebay sells stainless heat coils you can install inside your woodburner, or a copper winding outside your chimney will work. the stainless coils are by far the most efficient option IMHO. The larger the heat coil diameter the better!
Barring the two foot (or greater) drop to the heat source a small 1/25 hp pump can run round the clock for pennies, link the tanks as previously mentioned with the low end of the source being the input to your pump.
Be carefull in a thermosyphon system to avoid air traps in the line as they will bring flow to a halt. A constant uphill gradient is an absolute requirement if it cannot be achieved than a pump is required.
Don't forget this system cannot be sealed or you will create a bomb, a small one if the storage is plastic, a huge one if you have sealed metal drums, an open j breather in the top of each tote or drum will keep pressure from building. IF you have CERTIFIED RATED components ( pressure rated) you can get by with a common water heater Temperature and Pressure valve in every tank.
Also if your system has any ferrous metal in them each new flow of fresh water will increase rust in the system, boilers operate for years via oxygen depletion...and chemical inhibition, a fresh flow / domestic water system has neither option.

Thanks for the information. I was planning on using the thermosiphon idea. I have plastic containers for the water and planned on leaving a breather so the system would stay open.

Why do you want to keep the water barrels warm over night?  I'm assuming it's so that they bleed off heat to the greenhouse?  If so, would it be easier to directly heat the greenhouse with your heat source instead of putting it into the barrels?  

I'm struggling with different ideas to store/release heat myself so that's why I'm curious.

I do want to store some of that heat in the water. It will hopefully heat the greenhouse as well while I am heating the water. My thinking is that by heating the water it will help hold over some heat and help get a little extra time overnight without having to stoke the fire

I think you would find it effective and easier to have separate thermal mass in contact with the water tanks and heated by the fire. A rocket mass heater will burn cleanly (no creosote to condense inside flue channels) and heat a masonry or cob mass, warming the water, while absorbing some heat from the water during the day. No water coils or piping logistics needed. The masonry mass will hold its heat overnight with only a fire in the afternoon/evening, no need to keep burning all night.

Thats something I've always wondered.
Has anyone tried using a glycol mixture as mass in a rocket mass heater?

I am planning on using a small rocket mass heater and embedding the coils into the mass. If I use the thermosiphon to circulate the water into different reservoirs, my thoughts would be that I could have a smaller heater. I have a small greenhouse so I am trying to keep size a consideration.