Question for those using "in slab radiant"

[gradwell]

I am using an Econoburn 150 to heat about 4500 sq. ft of in slab radiant. Once the slab is up to temperature, is it necessary for me burn day and night long everyday? I figure once the slab is upto temp. it should stay there for a little while so could I get away with burning every other day or burning just during the day to recharge and letting it burn out for the evening.

My initial concern from reading here at the Hearth is that it appears to be very critical to keep return temps. above 140 deg.. That being said, each restart would be allowing another opportunity to be below that mark. Is this correct or is it only really a concern when the boiler is up and operating at higher temps.?

I guess I ask these questions as it seems that if the slab is upto temp. and the boiler is sitting in idle, I am wasting wood and creating creosote. Also, being new to wood burning, I havent become totally comfortable with leaving the fire unattended just yet, which makes for a long night. My third issue is that I work all day and have nobody to tend the fire for me which leads to even more ideling. Actually, I am a prime candidate for storage. I understand that now and will consider that in the future, but for now I am wondering if I can get away with the above scenario.

Thanks for the help!

 

[2.beans]

i think you need to give some more info like heat loss and maybe how its plumbed and youll get so good answers.

 

[gradwell]

Thanks 2.beans, I unfortunatly did not do my calculations nor install so I have no clue as to how to answer that. I could tell you that I shut it down for 1 night and lost 1 degree of wall thermostat heat, but I am sure you are looking for BTU loss which I can not answer. As far as plumbing, I can tell you that I have 5 zones with 5 loops each approx. 300 feet per loop 1/2" pex. My boiler is located 220 ft. from house and is supplied with (2) 1 1/4 pex and returned with the same. I am sure I could answer other plumbing questions, just dont know what else is needed.

For me, bottom line is that due to my circumstsnces, I must continually load boiler with wood as I am not available to burn shorter fires. Because of this, now that the floor is uptp temp. I have little need for heat. Therefore, I am ideling near constantly which I know is affecting my heat exchange tubes in the boiler. Besided general inconvenience, these Econoburns dont seem to be the easiest units to get to heat exchangers to clean.

So all of that being said, this is why I was wondering about being able to shut down the boiler and ride the heat stored in the slab.

Thanks again for the input. I need it!

 

[jebatty]

The return water temp issue is easily resolved by installing return water protection. Storage likely would solve most of the rest of your issues. But more info also needed to be more precise.

 

[gradwell]

Thanks Jebatty, In my scenario, the boiler is shut down completely, so at that point, how would return water protection help?

I did shut it down last night at 11 PM. Outside temps. 35 deg., house temps. 70 deg. Started this morning at 6 AM At that time interior boiler temps. 103 deg., return temps were the same (103) and house temps 69 deg. and outside temps. 31 deg. I started fire and about an hour later was ideling. All manifold temps. were where they normally operate 100 deg. zone supply and 80 deg. zone return.

My biggest concern is that each day I would shut down, boiler temps. would fall below the 140 mark until I refire. Is this a problem? From my interpretation of what I read here, I would say it is, but maybe I am missing something. My alternative at this point is to be in an idle situation for the majority of the day and night.

Thanks again!

BTW, I know you are all looking for more info, I just dont know what that info is or if I know the answer to it. I am pretty familiar with the layout, I just am not sure what yourlooking for. I am new to wood and boilers and had the system installed by a third party. Therefore, not as experienced as most with this stuff. I will figure it out eventually.

 

[jebatty]

Boiler return water protection recirculates boiler supply hot water back to the boiler to insure that all return water when mixed with boiler supply water is higher than 140F, some say it should be up to 160F. Of course, a cold start will have boiler water below 140F and that cannot be avoided. But the boiler will heat quickly, and then return protection will insure that system return water does not lower boiler return to less than 140F (or higher).

 

[flyingcow]

You may have it already installed? The mixing valve to control your return temp to boiler that is. Seems any installer should know that this is an important part to a wood fired boiler. Should be in the same room as boiler. Basically loops water round and round (out of top of boiler to the return inlet of boiler, on the bottom) until temps are where they should be, and then ships the water into your radiant slab. If you have that then you should be all set.
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But i'm not much of an expert on this stuff, and I have a really sh!tty way of trying to explain things. Mainly because i only know enough to get it wrong.
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But if you get this returning right, i think you should be able to let the fire go out while your gone and then fire up when there. You kind of have storage, it's your radiant slab. Just takes a little practice on doing it. Once house cools off a few degrees and depending on weather outside, you'll build a big fire and bring everything back up or on a warmer day, only fill firebox half full and give the slab a little bump of heat to get you thru the next 24hrs. Basically the same thing i do with my storage tank. Cold ass days, i come home and fire and fill the boiler once, sometimes twice on the same night(-40 below nights). Takes a little bit of figuring it out. This will aloow full burns with minimal idling which will keeps your hx tubes from needing to be cleaned so often.

 

[Gooserider]

Essentially the return water temps are most critical while the fire is burning and gasifying strongly... That is when the most water vapor is being produced both as a combustion byproduct and from driving the remaining moisture out of the wood... At this point there is lots of moisture to potentially condense, and its the condensing that causes the problem...

Yes, you will be below condensation temps for a few minutes when first doing a cold start, but the boiler should rapidly come up to full temps (especially if you have return protection properly installed and operating) and drive off any condensation before it really has a chance to cause any issues...

At the end of the fire as it is burning out in the coaling stage, the temps may drop below condensing, but the wood will have no moisture left in it, and almost all the hydrocarbons will have been consumed - the primary reaction at that point will be C+O2 -> CO2 + heat, so there won't be a significant amount of water vapor to condense...

The key issue that you really need to figure out is whether or not you have any boiler protection installed, and if it's working properly... To see if you have return protection, follow the supply and return pipes coming out of the boiler - do they have some kind of cross-over within a couple feet of the boiler, with some sort of valve or circulator on it? (good) Or do they go straight to the house with no connection between them? (bad)

The way to see if you have a temperature is to monitor the return water temperature, put a sensor of some sort on the return pipe to the boiler and see what it does... It doesn't have to be fancy, a cheap kitchen thermometer clamped to the pipe and wrapped in pipe insulation will do... If you want to distance monitoring, some have used one of the digital meat thermometers with the radio connection to a remote readout...

It really doesn't matter what is on the other end of the boiler piping, what matters for this is the temperature of the water returning to the boiler...

Gooserider