Cheap way to temper water temperature in a hydronic system

I'm in the middle of building a TLUD powered boiler.
It's installed in the greenhouse and intended to heat the water in the wicking beds.

The heated water will be stored in water heater tanks.
Bringing it to a boil will store the most energy, but the plant roots won't like being boiled.
Proper hydronic systems use mixing valves but not only are they expensive,  I'm not sure they will work in a low pressure system, which is what I'm building.

Is there a simple technology that could work in this application?

What does this mean please?

a TLUD powered boiler.

Why not heat the water to a lower temperature and have rocks in the same water to hold heat?
The higher you heat the primary source of the water the greater will be the heat [ energy ] losses also.
I am thinking by using rocks, to temper changes in temperature, less heat will be used, and the plants will not cook.

Can you install a series of barrels painted black and positioned to receive sunlight in colder weather, and are shaded when not needed? I've seen youtube videos where the water barrels are both thermal mass and a water source and one where a wallipini had a gutter catching the rain off the structure feed into the barrels, and plumbed the barrels together with an output below for watering. If you have a method of circulating the water with say a pump, you could have another heat source like a wood fire under a metal container, and pump the hot water down a line that distributes the hot water back into several barrels, and those barrels mix their outlets to feed back into the heater. Cob Cottage had a rocket mass heater for hot showers, they had a hot water tank buried in cob sitting above the heat riser from what I recall, and it wasn't sealed/pressurized. The cob surrounding it helped retain the heat longer too. So if you have the tank input come from a line that takes water from several tanks, and the hot tank output splits evenly back to those tanks, you could add hot water in small quantities based on the pump flow.

John C Daley wrote:What does this mean please?

a TLUD powered boiler.

TLUD is short hand  for a Top Lit Up Draft charcoal making retort.

They are very simple retorts that make charcoal by the batch and produce heat that is easily used for cooking.


I made one from a stainless steel stock pot and now I'm building a contraption that captures the heat in water.

I have two water tanks at hand, one insulated,  one not, amounting to another 80 gallons over the   30 or so that boiler holds.

If the un-insulated tank is filled with stone, the stone could absorb some of the heat and the naked steel could radiate some as well.
More heat at the roots and less in the air is preferable, so maybe this isn't the solution I need

So maybe I  wont use stones to temper the water, but I could increase the amount of water heated to the point that it will be unlikely to get very hot at all.
What the right temperature would be is another matter.
Rooting tempatures for hardwoods can be from about 55 to 80F with 70 considered ideal.
Dissolved oxygen goes down as the heat goes up, and treating potted plants for pests by  dunking them in 120F water till the root ball gets to 115 degrees  seems to be an accepted practice.


I could rig a pump to circulate when the water in the boiler got to 80 and stop when it got below 70.
This would let me evenly heat the entire system to an acceptable level.
Its another expense, but much cheaper than a tempering valve.
I might even have all the components already.

I could even add other heat sources, like a solar PV driven coil or a solar thermal water heating collector.

William, your system is superb, kudos for the ingenious capture of that heat. Your work is inspiring and clever.

I am trying to picture your no/low pressure idea, but may I ask for more details? Admittedly I am not the sharpest knife in the drawer ........Could you please show us a rough sketch?  

R.Hill