Seton W100 return temp. Mixing valve needed?

[byrddogwi]

Does anyone out there have a Seton or clone, with no storage, that has a mixing valve or Termovar to keep their return temps above 140 degrees when connected to a radiant slab?

I have a 3 year old Seton W100 that I am starting a second season of heating. Last year I had a ton of problems with it so I pulled off the side panels and put new insulation in it, cut them so I can access the heat exchanger and sealed the sides and top, the draft and the front door. I have 21' of 8" chimney and it pulls a draft of .06-.12 " WC.

I notice that if the slab is not calling for heat it will get up to 180-190 and cycle the draft as it should When the slab calls for heat it drops the temp way down to around 120 degrees before it climbs up. Right now it was in the mid 20s last night. I filled it up around 11pm and at 6:30 am it was down to a few coals and a water temp of about 80 degrees because the slab was calling for heat. I am using 150 feet of 1" thermopex pipe buried 4-5 feet deep between the boiler and the house so that should not be an issue. I am using hardwood, mostly dead elm, no softwood. I noticed last night the exhaust temp was around 300 degrees with the draft open and no heat load. I have not been home enough to watch the exhaust temps that much but they seem to be under 600 degrees so far.

The heat loss calc for my building from -30 to 70 degrees is 48K BTU. It is no where near that cold and I have not turned my heat on upstairs. I am concerned that I will be building up creosote again in the back as I did last year and I will be scratching my head and running electric heaters to supplement when it gets 20-30 below zero. I also notice that when it is that low and I add wood it takes a long time for it to come up to temperature. I did not have time this morning to watch how long it took to get up to temperature when the slab was calling for heat (maybe it did not until the slab was off). I have seen other posts that say that the seton will come back quickly. Last year I had seen a similar situation where it would drop the temp to about 120 when the slab calls for heat and it may not get back up to 180 even after an hour of so.

Would a mixing valve or a Termovar on the return solve my problems with the seton creosoting up and the slab dragging the seton water temps down? How would I connect it in to the return of the Seton? My guess is I would connect the mixed port to the return going into the seton return, the cold to the return from my radiant and the Hot to the supply of the seton.

Thanks for any information. I have not been able to get a hold of Fred since early this spring. I had been trying to trade up for a bigger Seton since the end of last year, sounded like that would not be a problem when I purchased this one (if needed) but I have given up on that idea. I tried to contact him numerous times this spring and summer (phone and email) and never heard from him, sounds like a few others have had better luck. Sounds like I am stuck with this one so I am trying to make it work. I don't know if it is the stove (probably not) or just the way it is with a radiant slab.

 

[2.beans]

do you have a mixing valve on your radiant zone? if so turn it down so the slab gets cooler water. it will make it run longer but wont kill the seton. i have a shop floor thats 1600 square feet that i cant use because the tubing or amount of tubing is wrong. i havent tried to run it know that i have 1000 gallons of storage. maybe its not the boiler but the radiant setup. just a thought im no plumber.

 

[mpilihp]

When the slab calls for heat does it circulate water through the WB until it is satisfied? I would think that the circulator on the WB would be controled by an aqustat on the wood boiler and it would shut off before it got below say 150 (whatever you pick but id keep it high for DHW if you have it in the boiler) This would allow the wb to build temp back up quicker. Also as 2.beans said there should be a mixing valve on the slab zone to mix the temp down as from what ive been told you dont want to heat a slab with 170+ temp water, I was told to run 120 deg water in radiant heat zones.

~ Phil

 

[byrddogwi]

When the slab calls for heat does it circulate water through the WB until it is satisfied? I would think that the circulator on the WB would be controled by an aqustat on the wood boiler and it would shut off before it got below say 150 (whatever you pick but id keep it high for DHW if you have it in the boiler) This would allow the wb to build temp back up quicker. Also as 2.beans said there should be a mixing valve on the slab zone to mix the temp down as from what ive been told you dont want to heat a slab with 170+ temp water, I was told to run 120 deg water in radiant heat zones.

~ Phil

The Seton has the boiler pump running 24/7 but it could be setup with a snap disc or aquastat, although it would probably cycle the pump a lot. I do have a mixing valve on the radiant set to 140-145 degrees. I set it at that because it has a parallel header that runs the staple up and the slab. The staple up shoudl have at least 140. I may need to re-plumb the radiant so I can add a mixing valve for 140 and one for 120 for the slab. I was hoping I could get by with one feeding both at 140. The slab never gets that hot that I am not comfortable walking on it. Most of the time the return of the slab is around 80 degrees unless it has been off for a long time, then it could be as low as 60 degrees.

I have my boiler as a primary circuit and the radiant as a secondary circuit.

 

[mpilihp]

Im no expert but I think a mixing valve on the return to the boiler would server two purposes. First protect the boiler from condensation inside the boiler and having it rust through. Secondly maintaining a higher return temp would help the boiler recover and maintain a constant temp and not swing widely like your seeing.

~ Phil

 

[Willman]

The slab never gets that hot that I am not comfortable walking on it.

What type and how thick is the under slab insulation ? Any perimeter (footing) insulation? With the water temp your running thru slab it should be warmer than necessary. Huge delta T could be another issue pointing to inadequate insulation. Not a pro just my opinion.

Will

 

[byrddogwi]

The slab never gets that hot that I am not comfortable walking on it.

What type and how thick is the under slab insulation ? Any perimeter (footing) insulation? With the water temp your running thru slab it should be warmer than necessary. Huge delta T could be another issue pointing to inadequate insulation. Not a pro just my opinion.

Will

The slab has no insulation under it, that is the way it was. There is not much I can do about that, is there? I was going to put 2" of closed cell foam 2 feet down and 2 feet out around the edge but we ran out of money to do that this year. I may just try to put some polystyrene around it or straw bales and get to insulating the perimter next spring. I know that edge insulation will drop about 10K BTU/hr at -30 degrees. Even with no insulation under or around the edge the heat load calc shows 48K BTU heat loss at 30 below zero.

I may have to install a mixing valve or a pump and bypass on the boiler to keep the return temps above 140.

 

[Willman]

The slab has no insulation under it, that is the way it was.

This is your main problem. Not certain of any fixes.
Will

 

[SteveJ]

My storage tank is not currently finished but my plumbing diagram with two mixing valves - is in the thread https://www.hearth.com/talk/threads/26048/

Both mixing valves are Honeywell AM-102R-US.
The radiant floor mixing valve is set at 120F.
The Seton W-130 return mixing valve is set at 140F.

The only issue I have ran into is to make sure the radiant pump pulling through the mixing valve is only running when one of the heat supply pumps is running as discussed in the link above.

Thanks to nofossil for the control layout to ensure this operation.

 

[2.beans]

my 40x40 slab that was insulated with 2" blue insulation and a radiant that doesnt work. it kills my boiler and never gets the shop hot. tried all kinds of temp settings with the mixing valve and have tried different size pumps with no real luck. altough the larger pump helped the most it makes the hot water move thru the slab faster so the slab cant suck all the btus out so quick. without insulation underneath i dont know what you could do. if your radiant tubing in the slab is right at the bottm of the slab once it gets ground water touching it will kill the water temp.

 

[trailhound68]

Sounds familiar fellas. I have a 700 sf radiant floor w/ 2 long loops and marginal insulation underneath. It will easily heat the space, but it is a huge draw on the system. I have experimented and learned some ways to manage it.
First I tried a thermostat on the wall to control the circ pump. The demand cycle is too long, the water gets cold, then gets dumped to the boiler.
Second I tried a timer. Same scenario, but not such cold water retuning from the slab. Frequent cycles on/off. Big improvement.
Now I avoid using the floor circ pump, and rely on my house circ pump to handle it by adjusting ball valves and forcing some amount of supply through the floor loop. Luckily my old Taco 110 has enough ass to make this happen.
The idea is to create a constant flow (demand). It will always bring back cold water, but a little bit all the time doesn't wreck your temps.
It works pretty well.

 

[Willman]

my 40x40 slab that was insulated with 2” blue insulation and a radiant that doesnt work.

2 beans Do you think 2" isn't enough ? Do you have perimeter insulation around footings that extends deeper into soil ? What do you mean by "radiant" that doesn't work ? Thanks
Will

 

[jklingel]

First, ouch. No insulation under the slab sounds like an endless fight. This site (http://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm) talks about the need for peripheral insulation on a slab, as that is where the bulk of the heat loss is; you may want to read there, too. A comment on the continuous circulation. I've been reading on the healthyheating.com site and that is apparently the recommended way to heat; circ all the time, regulate the water temp. Good luck; wish I knew more to help out.

 

[byrddogwi]

Thanks for all of the info.

I recently purchased a LUX digital wall themostat and removed the thermistor. I connected 20' of CAT5 (I have extra laying around) cable to the 2 connections on the circuit board and then the other end to the thermistor and feed the wire down a pex tube that I had buried in the slab. I probably got it in about 10-15 feet. I have the new "slab" thermostat set at 81 degrees in parallel with the room thermostat which connects to a 2 zone controller. It is working great! The room seems much more consistent and I am burning less wood now that the slab is a more consistent temp. The room thermostat is set for 70 and it usually is around 72 at that thermostat. I probably don't need the room thermostat but I am going to leave it in to check the room air temp at that location.

The problem is as solved as it is going to be until I can insulate around the slab this spring.

 

[trailhound68]

What I had learned from my screwed up system, which I built, is that if you use a thermostat to control room temps it 'idles' for too long. The water loses its energy and then gets sent back to the boiler quickly.
Maybe try a constant slow circulation at a lower temperature, it seems to work well with mine.
Whichever method, It's a big demand.