Indoor wood boiler with in-slab in-floor HELP

[derrick351]

hello i have a northern leader indoor wood boiler. it is a smaller of the three models they made. i'm having a hard time finding people who have the same or similar set up. the problem is i'm not heating up the square footage (approx 2200) as well as i'd like. i have 2" foam around and under the 5" slab. 1/2" pex 7 loops total. two zones. primary loop is 1 1/4" copper. i have a commercial 1 1/4" mixing valve. the problem i'm running into is when the pumps kick on it's pulling all the heat out of the stove. i basically have to run the wood stove at wide open with the ash pan door open. it does not have a blower as a damper it just has a mechanical knob with a chain that raises and lowers the draft door. i was wondering if i should be running the pumps non stop (which i have) or run the stove at lets say 180 degrees and 165 as the shut off(which i have and by the time the return water is warm the boiler is at 165). not sure if adding more volume with a storage tank would help or if i need a bigger indoor boiler or if i just need to go with an outdoor stove.

i'm also having a problem with the mixing valve. it's a honeywell globe with an electric accuator and a honeywell stand alone electric control box. when the pumps kick on the plunger on the mixing valve is in the wide open position because the control box is calling for heat because the pumps haven't been moving water for lets say 15 minutes. so the pumps kick on and the stove emptys 180 degree water until the sensor(which is strapped to the outside of the copper pipe right after the mixing valve) gets warm enough to have the actuator throttle back the hot and mix it with the return to get the desired 130 or whatever. i will be ordering an emmersable sensor that actually goes in the hot line right after the mixing valve. i'm hoping that will make the stand alone controller react faster.

any help or insight would be greatful

 

[maple1]

You'd need good thermal contact between the sensor & the pipe, and likely also insulation around it (around both the pipe & sensor as a unit) or else the sensor will always see cool on the area of it that is not contacting the pipe. Is it well insulated? The pipe itself shouldn't cool all that much in 15 minutes of non-flow if it is well insulated, the sensor needs to see the same.

 

[derrick351]

I just have the sensor zip tied to the 1 1/4 copper about 7 inches downstream from the mixing valve. I will be ordering the sensor that actually goes in the pipe. I believe the sensor I have is best used for air temp. I have a temp gauge in stream and it reads 13 degrees warmer. Here is a pic of my set up. The indoor wood boiler is on the other side of the wall.

 

[derrick351]

Here's another pic

 

[GENECOP]

I think you need storage......I am a novice to the wood boiler as well, but returning the water directly to the stove does not seem correct.....if you had an indirect HWH that the stove heats up and all the radiant pulling off that instead of the stove...would probably be better....as far as the boiler size, if it is speced to your size home and heat loss you should be OK.....

 

[Coal Reaper]

yeah you need insulation. the copper dissapates the heat quicker than you would expect. i have an external sensor ziptied for a set-point circ just the way you have it but with 1" of insulation all around and it works fine.
and this is mixing valve for the floor right? not boiler? look into loading unit for boiler.
no need for OWB.

 

[maple1]

I think I would first move that sensor closer to the mixer, and insulate it well. That might fix some or most of your problems, easy peasy. I have an aversion to cutting pipes that contain water, unless I REALLY have to. So try that & re-assess.

And if your boiler is not getting & keeping your house warm, there are other issues to sort out before even thinking about adding storage (that we don't have enough info to comment on) - as there is no extra heat to send to storage.

 

[derrick351]

what is a loading unit? just recently i've been running the primary pump, and each of the 2 zone pumps non stop. and the boiler when it gets around 0 degrees outside can hold water temps around 100-110 degrees, but that is running the boiler wide open (ash pan door and dampers open) which keeps the house at 68, i'm just worried that when it gets sub zero temps outside it might be too chilly in the house. so that eliminates the mixing valve/sensor from the equation because it is in the wide open position. so unless i'm missing something, the boiler just doesn't have the volume?

 

[maple1]

A loading unit is a thermostatic valve body with a built in circulating pump. It is designed to circulate water through the boiler while maintaining a certain minimum boiler return temperature (usually 140°). Usually used when storage is used.

Slabs take a huge amount of heat to get up to temperature the first time. I don't know anything about your boiler - so maybe it doesn't have the output capacity? We also don't know anything about other things on your burning side like what kind of wood you're burning & how dry it is, your chimney type & draft, and flue temps. Etc. etc...

 

[derrick351]

i can't find the output capacity on the boiler. Its a Northern Leader HW 16-23. i beleive it says on the tag that it is 15 sq ft of heating surface. 2 year old seasoned hard maple and some ash. chimney is cinder block i beleive the flue is 9x13. i don't have a damper in my 6" stove pipe. The damper on the stove is a sampson 5D damper control. it's a manual damper twist dial. don't know flue gas temps. wondering is a stove pipe damper will keep some of the heat in the stove instead of all up the chimeny.

 

[Armaton]

Did this system work before? I don't quite understand your electronic mixing valve. The only purpose it should have is to take the 180 degree water from the boiler and mix it with the in floor return water down to a certain temperature! If it is allowing significantly hotter water through, it is faulty. Your picture shows a Tridicator just downstream of your mixing valve, check the water temp during the cycle. That should give a good indication whether the mixing valve is working properly. My guess is that the system was designed to "SIP" from the boiler once the return gets to temperature. Doesn't take much 180 degree water to get 90-95 degree water back to 110 degrees. Your boiler probably could keep up with that demand. At initial start up there will be more of a demand from the boiler, because there is 50-60 degree water in the slab. But once the floor starts heating, the return water should catch up fairly quickly and be only about 15% cooler than it was when it went into the floor. At least that is what was explained to me. Just my 2 pennies. The experts will probably shoot all kinda holes in my theory though!

 

[derrick351]

the problem with the mixing valve is the fact that it's reaction time is so slow. when the aquastat on the wood stove his 180 and turns the pumps on the controller for the mixing valve is calling for heat because the pumps were just off. so the mixing valve is in the wide open position. That causes the wood stove to dump a lot of heat all at once. until the sensor reaches the desired temp and by then it has been letting 180 degree water into the floor. if i run the stove all the way down to say 110 degrees the mixing valve with modulate properly once it dials it's self in. but at 100 it kills the fire unless i'm running it hard with all the dampers and ash door open. i am wondering if the emmerable sensor (the one that goes in-stream) will react faster than the sensor i have zip tied on. the electronic controller allows me to put in a minium % output. which if it was a maximum output i could set to say 15% so it would never let the mixing valve open more that 15%. i have the commerical techs at honeywell stumped also. one of them suggested that i run the pumps non stop and which would let that mixing valve modulate correctly but it kills my stove so bad that unless i'm there throwing woood at it non stop it won't get the job done and keep the output temps at like 90. but a couple of times it has warmed up the return temp to the point where it starts to climb to 140 and i have to actually shut the ash door. so i know it's capable.

 

[maple1]

Did you insulate the probe?

 

[BoilerMan]

Can you draw a diagram or your piping setup? can't tell what you have going on by that pic, or more pics would be helpful. What model is your actuator and controller?

I heat an 8" thick 2200 square foot slab with wood exclusively. Had a 130,000 btu conventional wood boiler previous to my gasser.

You should be piped primary/secondary with a slab, then you can mix down to slab temps.

TS

 

[Armaton]

the problem with the mixing valve is the fact that it's reaction time is so slow. when the aquastat on the wood stove his 180 and turns the pumps on the controller for the mixing valve is calling for heat because the pumps were just off. so the mixing valve is in the wide open position.

I ask again, did this system work before this problem? Bear/bare with me, just trying to understand. So, the stove temp is running the pumps, not a call for heat from a thermostat? ( Or both)? How would the system react if the house was up to temp, and the boiler was at 180 degrees, would it just keep pumping more heat into the floor, or shut down the stove, is there a safeguard to prevent overheat? Would a lower launch temp setting on the boiler aquastat possibly help? That way the boiler would have longer to "Catch up". Just read about globe valves, is it appropriate for this application? A globe valve is designed to close slowly to prevent water hammer. Is this different for a 3 way globe mixing valve utilizing an actuator? If not, you may always have a problem. All I seem to have is questions, no answers. But as I said, trying to understand! Maybe just a mechanical mixing valve set to 110 degrees, with a dump zone for possible overheat?

 

[derrick351]

Can you draw a diagram or your piping setup? can't tell what you have going on by that pic, or more pics would be helpful. What model is your actuator and controller?

I heat an 8" thick 2200 square foot slab with wood exclusively. Had a 130,000 btu conventional wood boiler previous to my gasser.

You should be piped primary/secondary with a slab, then you can mix down to slab temps.

TS

electric controller is a T775M2048 and the actuator ML7984A4009. on the back side of that wall is the wood boiler with the supply (hot) coming out the top of the stove going into the globe mixing valve. the return from the floor tee's right before it goes into the mixing valve and one side of the tee goes back to the stove divided into both bottom ports on the back of the stove.

 

[derrick351]

this system is brand new. last winter i had just one zone running. this year i made the 2nd zone live. last year i did not have the actuator on the mixing valve and left it in a fixed position. which was in the plunger almost all the way up position. but i was only running boiler water temps of 145ish. it didn't struggle to keep that one zone heated but i was afraid of over heating the system so i didn't run higher boiler temps like i wanted to. over heating has not been an issue this year since i have the 2 zones going. i had 2 days off and the first day was cold outside subzero morning temps. i feed the stove ALOT of wood with ash door open to try something. i set the controller temp to 133, which is 140 on my in-stream temp guage. by the way, i wrapped insulation around the sensor and it made it instead of 13 degrees different from the instream to now only 7 degrees off, didn't really do anythiing for the reaction time. anyways i heated up the stove to 180 then set it to run all the way down to 120. i did that twice and the second time i had a good hot fire and the slab warmed up to the point where the return temps didn't kill the stove but actually was giving continuaous 140 degree water and the stove temp was rising so i closed the ash door but kept the other 3 dampers open and got the stove to stick around 140 for a while until it did not get enough air and the fire died and the temp dropped. i thought i could regulate the fire intensity with the sampson 5d damper control. but it at wide open would not give enough air to maintain 140 degree boiler temp. one issue might be that zone one which i didn't install tubing, is spaced too far apart. it's approx. 1450 sq ft and it only has 3 loops. the second zone i have each loop covers less that 300 sq ft. which holds heat and heats up faster. the first zone was done in 2007 when i believe the rule of thumb was 500 ft per loop. i do not have a dump zone partically because unless i'm really rallying the stove i don't have to worry about it overheating. i believe i do need a 3-way valve that doesn't allow return temps to come into the stove less that 140. then run the zones on thermostats.

Armaton
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Joined:
Aug 22, 2011
Messages:
119
Loc:
Hastings, Michigan
New
derrick351 said:
↑
the problem with the mixing valve is the fact that it's reaction time is so slow. when the aquastat on the wood stove his 180 and turns the pumps on the controller for the mixing valve is calling for heat because the pumps were just off. so the mixing valve is in the wide open position.Click to expand...
I ask again

I ask again, did this system work before this problem? Bear/bare with me, just trying to understand. So, the stove temp is running the pumps, not a call for heat from a thermostat? ( Or both)? How would the system react if the house was up to temp, and the boiler was at 180 degrees, would it just keep pumping more heat into the floor, or shut down the stove, is there a safeguard to prevent overheat? Would a lower launch temp setting on the boiler aquastat possibly help? That way the boiler would have longer to "Catch up". Just read about globe valves, is it appropriate for this application? A globe valve is designed to close slowly to prevent water hammer. Is this different for a 3 way globe mixing valve utilizing an actuator? If not, you may always have a problem. All I seem to have is questions, no answers. But as I said, trying to understand! Maybe just a mechanical mixing valve set to 110 degrees, with a dump zone for possible overheat?

 

[Armaton]

Seems to me that you are trying to put too hot of water into the slab, which is overtaxing your boiler! Your system doesn't seem to have much water in it, and you are trying to pump all the heat you are generating into the slab at one time, which doesn't seem to be working. Try setting your mixing valve manually to 110 degrees and monitor the performance. That way, as I mentioned above, the system is "Sipping" from the boiler instead of "Gulping". If it still can't keep up dial it to 90 degrees and see how it does. Both will heat the house, just takes longer. Granted, this still isn't going to give you boiler or overheat protection, but you don't have that anyway.