Constant Circulation - Bad?

reog

Member
Oct 20, 2014
12
ontario
May be a really stupid question but I am going to be replacing my current boiler this year and the more I read the less I understand. My boiler is running into a plenum in my forced air system in the house and also through a sidearm heater on my hot water tank. It couldn't be much simpler, hot water out the top through a temperature controller to keep the water above 140 in the boiler before its released to the rest of the system, into the sidearm and then through the plenum and back to the boiler for reheating. The question I have is whether its okay that I don't have a bunch of controllers to adjust or stop flow based on water temperature? The two pumps on the system run non stop at medium speed.

It seems that a lot of systems control pumps and valves to regulate water flow based on temperatures. Should I have something like that? I am hoping to add water storage to my system next go round, will that require me to add valves or temperature controls beyond what I have?

I have been pretty happy with the performance of my system with regards to heat and the amount of wood I burn. If it wasn't leaking water right now I wouldn't change a thing (Empyre Elite :() but adding storage I think will help longevity of a new system and perhaps save me some wood.

Thanks in advance.
 

3fordasho

Minister of Fire
Jul 20, 2007
942
South Central Minnesota
If your heat emitter is a water to air HX in your furnace plenum the hotter water the better. 180-200F and the water/air HX will really shine. Lower than 140f and then things get tricky with sizing on the HX and air flow through the HX. You can quickly run into the situation where the forced air out the vents feels cool and long fan run times even though you are adding heat to the house.
Temperature mixing controls are for in slab radiant heat and domestic hot water use to make sure you don't damage your concrete slab from too much heat or burn somebody using hot water for shower or washing. This is why heat storage works well with in floor slab heat because as storage temps drop off it still heats fine and extends the use of storage. A forced air furnace HX that only works down to 140F and you just lost that much storage compared with in floor heat that can go down to 90-100F and still heat.

It's all about finding heat emitters that can work with lower water temps so you can utilize that storage even when storage water temps drop off.

I installed one of these and have been pretty happy with their lower water temp performance. Too bad they are a little hard to find.
I got mine from Menards at one point but they no longer carry them:
https://www.htproducts.com/fan-coil.html (Menards had the rebranded to Whirlpool version, but they are the same as the HTP)
The other downside is you need multiple units to cover a typical house - they are like a radiator vs central heat.
 

3fordasho

Minister of Fire
Jul 20, 2007
942
South Central Minnesota
After re-reading your post I realized I didn't really answer your question about constant flow. If you have underground line losses you will have this loss consistently while the system is running. I turn my circulator pump on when there is a call for heat from the house and off when there is no demand. Constant circulation will also prevent freeze up if our system is prone to that - I run some glycol in this loop because of that potential but this is really only a concern when I go on vacation and let the boiler go cold. After running with this set up I think I would forget the glycol and just run the pump manually when I go on vacation.

As far as varying flow in the system maybe a need for that in a zoned system when more zones are calling for heat. I am sure there are other reasons that others can give feedback on.
 
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E Yoder

Feeling the Heat
Jan 27, 2017
443
Floyd, VA
Just about any outdoor boiler (that style) needs constant flow through it to prevent layering and uneven temps (boiling on top, cool in the bottom).
 

reog

Member
Oct 20, 2014
12
ontario
Okay, sounds like my system is okay for me at least. Efficiency is good but as I suggested I don't seem to burn way to much wood or anything with the setup I have. I just want to make it easier/better for my boiler by adding the water storage. Seems like it may be pricey to make it happen though. The prefab tanks are not cheap.
 

hedge wood

Member
Mar 1, 2009
120
Eastern NE
On my Garn system I have six systems that come off my Garn from four heat exchanger's in four furnace's , in slab heat in my shop to a flat plate on my hot water heater. All my systems turn the pumps on and off as the need for heat is called for including my domestic set up. I think storage works better for folks that can use lower temp water for there heating needs. Exchanger's in furnace's sure work a lot better with 160-190 water than when the water temp is down to 120-140 in the tank. You may want to save your money and skip the storage and keep running like you have been .
 

salecker

Minister of Fire
Aug 22, 2010
1,197
Northern Canada
Decommissioned propane tanks make great storage tanks.