ILboilerguy
New Member
Hello everyone. I recently installed a water to air exchanger in the plenum in my propane furnace. Is it okay to run the propane woth the heat exhanger in the plenum
Outdoor wood boiler heat exchanger
- Thread starter ILboilerguy
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Wouldn't you then be heating your outdoor boiler with propane?
Bill G
ArboristSite King
What the hell? Not at all
ILboilerguy
New Member
In reference to the boiler not being fired yet
That would depend on whether or not the circulator pump is running.
Bill G
ArboristSite King
The pump can still be running and you are not heating to he boiler water at all. It is no different than your truck. The only time water is circulated through the heat exchanger is when the water temp coming from the boiler is high enough for the the thermostat to open and allow water flow.
Never seen one with an automotive style thermostat installed.
I have a water/air radiator deal in my forced air furnace in the house and you can absolutely run the LP while it's in there. I put a mechanical aquastat inline from the thermostat that stops the LP from firing when the fan runs when the water temp is above 120f. If it drops below that the LP fires too keep the house warm and it will absolutely heat the water going back to the stove if the circulators are running.
There are outdoor boilers that have a bypass so the water only leaves the stove when it's above a set temp. Never seen one but I know it exists. Most outdoor boilers are installed such that the water is always circulating no matter what temp it is.
I went on vacation last year in January and left the circulators running and the stove water stayed in that 85f range. The water heater sidearm tossed in some heat, the forced air furnace tossed in some heat and the in floor boiler put in a little more. So much so that the LP boiler in my farm shop barely ran as the stove water was warm enough to keep the floor warm up there. Although it worked it wasn't something I want to do often as it has to be hard on the heating appliances in the house in one way or another.
There are outdoor boilers that have a bypass so the water only leaves the stove when it's above a set temp. Never seen one but I know it exists. Most outdoor boilers are installed such that the water is always circulating no matter what temp it is.
I went on vacation last year in January and left the circulators running and the stove water stayed in that 85f range. The water heater sidearm tossed in some heat, the forced air furnace tossed in some heat and the in floor boiler put in a little more. So much so that the LP boiler in my farm shop barely ran as the stove water was warm enough to keep the floor warm up there. Although it worked it wasn't something I want to do often as it has to be hard on the heating appliances in the house in one way or another.
Bill G
ArboristSite King
I am waiting on a delivery right now while my phone charges. I will post a pic or two later. The grammar Nazi's will tear me apart for saying "thermostat" when I should have said "thermostatic solenoid"
Central Boiler perhaps ?
I asked a a few wood boiler buddies if they have thermostatic valves and got two yups and four nopes. Both yups had Central Boiler stoves.
As far as grammer nazi'ing goes ... It's more of a valve than a solenoid isn't it
OH_Varmntr
Burner of stored sunlight
Central Boiler perhaps ?
I asked a a few wood boiler buddies if they have thermostatic valves and got two yups and four nopes. Both yups had Central Boiler stoves.
As far as grammer nazi'ing goes ... It's more of a valve than a solenoid isn't it
When I bought my CB6048, they would not warranty anything on it unless the thermostatic supply/return valve was installed.
My circulator on the "boiler" ran 24/7 and the valve was installed where the supply and return line-set entered the heated space and if the water temp was not high enough (I think it was 145F) it would return the water back to the water jacket to be reheated.
Modern circulators have delta-T (differential temperature) tech on them so they vary their speeds to maintain a certain temperature drop across a load utilizing temperature sensors to monitor the loop supply and return temps. Most hydronic heating system heat exchangers are designed for 20F deltas so you aren't returning too cold of water back to that could lead to thermal shocking and micro-fracturing of the water jacket steel.
OH_Varmntr
Burner of stored sunlight
It depends entirely on how the system is configured. In some cases, yes you would absolutely be heating the HX loop water with your propane burners heating the plenum air.
If a basic system was installed with no thermostatic valve (which there are tons of those out there) and the water-to-air HX in your furnace plenum is not on a zone valve, then you would indeed be heating the water flowing through your HX, as long as the plenum temps are higher than the water temps, of course.
If a little bit better system is installed with a thermostatic valve like you speak, then it all depends on water temps vs plenum temps when it comes to the direction of heat exchange.
If a properly designed system is installed with a thermostatic valve and the plenum HX loop on a dedicated zone valve, then it will only flow water through the plenum HX in the event the system is armed and the thermostat calls for heat to that zone when the water temps are high enough to flow through the system and not directed back to the boiler.
In theory, you shouldn't be firing propane if your HX circuit is selected for primary heat. There are thermostats that have secondary or emergency heat settings but those are usually set up in a way that the primary heating system is locked out when the emergency heat is called upon.
It must not be forgotten that heat exchangers work in both directions. They both emit and absorb heat. The task they perform is entirely dependent upon the system temperature differentials.
Here are some pics of how I set my furnace up with an aquastat so the LP will kick on if the water temp from the stove drops below whatever I have it set at. Aquastat mounts to the hot water line from the stove.
A piece of 3-wire …
Intercept the white wire from the house thermostat and wire nut it to the red wire from the aquastat.
White from aquastat to W
Green to G
Use whatever thermostat you already have and change nothing on it. No fancy programming of a dual source thermostat or whatever they’re called. The thermostat calls for heat and the furnace fan starts up without the burner starting until the water temp from the stove falls below whatever you have the aquastat set to, then the furnace function’s like normal. It will of course be putting heat into the stove water as long as the water is circulating, which is good so the water and stove have a lesser chance of freezing. Clear as mud right lol ?
Is that working off of supply temp or return temp ? I have my mixing valves all adjusted so the return temp doesn’t drop below 145ish. Boiler set temp is 170 on 180 off.
Bill G
ArboristSite King
The valve opens (on the supply side) at about 140-145 to allow water to pass through and on to the exchanger. The boiler temp is in the 170-85 range but I have seen it hit 191 if we are getting a warm snap. I saw it go much higher one fall when some idiot did not check the water level before building the first fire of the year. What a fudgesicle that was.
did not check the water level before building the first fire of the year. What a fudgesicle that was.Similar threads
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