Questions about radiant heat system

[mx842]

If you would "properly" dry your firewood before burning it, you wouldn't have all that creosote build up...

SR

Yes I agree with that and at times I know the wood I burn may not be the best but it is what it is. During the day I open up the air intake to the stove and let her rip. If I have some wood that is not that dry that's when I use the not so great stuff. I add it in with some dry and at night I bank the stove with good dry wood and cut the air intake back to just enough to maintain a decent burn. It will normally burn down to nothing but coals by morning.

It's been hard for me to keep up with all the things I have going on and am still burning wood the got blown down in the last hurricane about 5 years ago. Hopefully I'll have all that stuff processed and stored by the this season. Some of the wood I'm working on now is on it's last leg and one more year on the ground it would be pretty much gone. Most of it is still solid in the center, that is if the termites haven't eaten it up and some of the logs I'm splitting now was 30" or more in dia. and now about 4 or 5 inches on the outside is reduced to mush but the center is still good.

 

[mx842]

I'm trying to be helpful here, and I read through all of your posts again, but I just don't see how having more water in the system helps. It looks like you've got a very good system and a simple change would make it work really well.

For the tank on the stove, you want it to quickly heat up and then hold its temperature. You want as little water as possible without causing big swings in temperature (boiling when the circulator turns off, rapid drops when the circulator comes on).

For the floor loop, you want just enough water to fill the tubing, any more and it just means waiting for the heat to take effect.

If you want to store heat, my recommendation is to heat the slab as much as possible and store the heat there. If you heat the slab to the point that it's uncomfortable to walk on, and the shop is still cold the next morning, then we can talk about other ways of storing heat.

You already have a circulator pump. I would add a thermostatic mixing valve Google and aGoogle. This will cost about $200 for the parts but will give you a really good system.

The aquastat connects to the stove tank, and the electric leads go to the circulator pump. Put the mixing valve so the valve output goes on the intake side of the circulator. The hot input to the valve goes to the output of the stove tank. The cold input to the valve connects to a tee, which connects the return to the stove tank and the return from the floor loops. I would start off with the aquastat at 160F and the mixing valve at 110F and then adjust.

When you start off, everything is cold, the aquastat is off so the circulator is off. The stove tank water won't circulate. As your fire warms, the stove tank water starts to warm. When it hits the set point of the aquastat, the circulator turns on, and the circulator starts water through the mixing valve. The thermostat in the mixing valve adjusts the portion coming from the stove and the portion coming from the return loop to keep the water at 110F. Whatever water is pulled out of the stove tank is replaced by water coming out of the loop return.

Once it starts running, look at how it runs and make adjustments. If the circulator stops and starts a lot, it means you're pulling more heat than the stove can provide. You want to get to the point where the circulator is cycling occasionally, that's the point where you're pulling the maximum heat your fire can support. Adjust the temperature on the mixing valve until either the circulator starts kicking off, or the floor gets uncomfortably hot.

If you get to the point where the floor is uncomfortably hot in spots but you still want more heat, a bigger circulator will pull more water and more heat.

If you get to the point where the water coming back from the slab isn't cold, then your limiting factor is the ability of the slab to absorb and radiate heat. This is where you can start talking about storing heat. Although I think your best way to store heat is to warm the building, so what I would look into is additional radiator capacity.

You also want to adjust the aquastat to the point where you don't get creosote buildup. That's probably trial and error.

Thanks I do understand what you are saying now. I have known all along that I would sooner or later have to add some controls other than just let the pump run all the time. I was just thinking that if during the day I could heat up three tanks of 160+ water the put a mixing valve between the last one and the manifold and send 90 to 100 degree water to the slab then by the time I get through the day with a hot burn and bank it for the night I would have at least warm water in the morning.

I think I may replace that 30 gal tank at the stove with that 50 gal tank I have and install my mixing valve into the system and see how it works. One question though, which end of the system would you add the mixing valve. Adding it to either end will require sending hot supply water to the manifold or sending the tempered return water through the long pipe runs between the two parts of the system.

Oh, and the mixing valve I want to use is a Leonard part no. 20470 {from a red tag attached the the valve} There is also a tag on the valve the says TM1513892 if that helps.

 

[CalG]

Why do you want to heat water in the tanks when the floor remains cold?

The logic defies me.

Heat the floor!

 

[mx842]

Why do you want to heat water in the tanks when the floor remains cold?

The logic defies me.

Heat the floor!

I know it may sound strange but my heater can make water that is too hot to dump directly into the slab. I don't know for sure what the ideal temp is that can be added to a floor but I have heard and read that you probably shouldn't dump water in a slab much hotter than 110/120 degrees max. With a wood stove it's hard to maintain a clean burn and keep water temps that low. I wanted a simple system with as few moving parts as possible and at this point I'm getting close I just need to fine tune a few things to where I can maintain a fire hot enough to burn clean but also do it as safe as possible.

If this was my house I would probably buy a boiler with all the bells and whistles and not have to worry about wood at all, just turn it on and let it do it's thing. But, this is my shop and as I have plenty of wood, still able and willing to cut it and also I'm in the shop more than I'm in the house so it's no problem keeping the fire going. I do go in at night though and as much as I don't mind messing with wood I still don't want to go out several times a night to keep the fire going.

I've been looking for some sort of tank that would hold around 500 gals of water that I could keep at 180/190 degrees that I could draw from then temper it down to 100 degrees and send to the floor. With that much storage I could run the stove hot all day and let it burn down at night and still have enough hot water to make it through the night and not be completely cold in the morning.

 

[swnoel]

I found a few pics that I took while I was putting this together and maybe they will make things a little clearer.View attachment 484889View attachment 484893View attachment 484892View attachment 484891View attachment 484890

Not trying to tell you what to do, but both relief valved should be piped towards the floor unless 2nd or 3rd steam or HW burns don't scare you!

 

[swnoel]

What's the calculated heat loss for the area to be heated and how many BTU's does that stove provide? Looks like you're trying to heat this area with a bit more than a match. Maybe an outdoor wood boiler would be more effective.

 

[pmsmechanic]

What's the calculated heat loss for the area to be heated and how many BTU's does that stove provide? Looks like you're trying to heat this area with a bit more than a match. Maybe an outdoor wood boiler would be more effective.

As I was reading the forum I was thinking the same thing. I'm not experienced with this kind of a setup but it looks overly complicated to me. It makes sense to me to store the heat in the floor instead of the water tanks. If the floor was warm enough then there would be no problem mixing the returning water with the hot water to a temperature that is suitable.

We used to heat our house with wood and had the same problem. I figured a 1500 square foot rated stove was more than adequate for a 1300 square foot house. I was wrong and on cold days it took forever to warm up the house. Later I find out that stove ratings are rather generous.

 

[quicksandfarmer]

I know it may sound strange but my heater can make water that is too hot to dump directly into the slab. I don't know for sure what the ideal temp is that can be added to a floor but I have heard and read that you probably shouldn't dump water in a slab much hotter than 110/120 degrees max. With a wood stove it's hard to maintain a clean burn and keep water temps that low. I wanted a simple system with as few moving parts as possible and at this point I'm getting close I just need to fine tune a few things to where I can maintain a fire hot enough to burn clean but also do it as safe as possible.

You're asking the storage tank to do the job that a thermostatic mixing valve will do better -- it will keep your stove hotter and your floor loops more stable. And you already have the valve -- I googled the part number you listed, I couldn't find that one but the TM series stands for "thermostatic mixer" which is exactly what you want. It may not be quite right -- the flow rating or the temperature setting may not be suitable -- but it's the right kind of part. You can get the proper one for around a $100 anyway.

The story with floor temperature is that you want your water to be as hot as possible without creating uncomfortable spots. A floor doesn't have to be much above body temperature to be uncomfortable to stand on. The hotter the water the more heat you can put into your space and the better the system is overall, so you want it as hot as you can stand. This will be set by the mixing valve, and you will set it by trial and error. (Which is another reason to use a mixing valve).

Here is a (very) crude drawing that shows the way I think it should be plumbed:



The only part you don't already have is the aquastat, which is going to cost around $100. I recall that in an earlier post you said you've got 2000 feet of tubing in the floor so you've already put a fair bit into this project between the tubing, the stove and your other parts. Just a little bit more and you'll have a really good system.

I've been looking for some sort of tank that would hold around 500 gals of water that I could keep at 180/190 degrees that I could draw from then temper it down to 100 degrees and send to the floor. With that much storage I could run the stove hot all day and let it burn down at night and still have enough hot water to make it through the night and not be completely cold in the morning.

As several others have said, you're better off storing the heat in the floor.

 

[bigdeano]

As several others have said, you're better off storing the heat in the floor.

How can you store enough heat in the floor to last all night? The floor has a fixed mass and you can't heat it to 180 deg. I think the OP has a good idea with the water tank if he needs to store heat.

I built a house with hot water heat in the concrete floor. I used a heat pump, so I didn't need to store heat, but if I did I would have probably used a water tank.

 

[CalG]

How can you store enough heat in the floor to last all night? The floor has a fixed mass and you can't heat it to 180 deg. I think the OP has a good idea with the water tank if he needs to store heat.

I built a house with hot water heat in the concrete floor. I used a heat pump, so I didn't need to store heat, but if I did I would have probably used a water tank.

The reasoning behind the "extra water will not be as good as storing heat in the floor" is due to the original system description that includes "cold water" returning from the floor. That is, the present system has not yet optimized the thermal mass available. Additional thermal mass will just continue the inefficiency. A warm water tank would be a great way to have some sensible heat available after the fires die down, but it will be at the expense of a "warm floor", and the even space heating a hydronic radiant system is renowned for.

That's the logic any way. ;-)

Bottom line, there is either not enough heat available, or the extraction and distribution of the heat output is under utilized. Either way, adding a water tank will NOT put heat into a cold floor.