boiler temp return protection question

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Mar 10, 2009
114
WV
I have a conventional wood boiler Energy King. Currently I have it piped into my gas boiler and then on into the house. I rarely use the gas boiler unless I am away.
The piping diagram that came with the install manual has no boiler temp return protection piping or mechanism for the wood boiler to keep the water temp up.
My question: Do I need to install return protection for this boiler. I have run this boiler for 2 years and it has done well. I have a large house with baseboard water heat and it keeps the house fairly warm. However, when its really cold the boiler has trouble keeping up because the fire is not always firing hard. If I manually open the draft and baby the fire for a while I can keep it rocking and thus keeping the house however hot I need it.
My pump is kicked on by aquastat set at 170. So a typical cycle is that the pump kicks on and runs and the water temp will drop as low as 120. It then will kick off and will not kick on again until the setpoint of 170 is reached (setpoint is adjustable). So if the fire is not burning hard it may be awhile before the pump sends more hot water into the house.
I'm not to concerned about corrosion due to low water temps but I am wanting more heat out of my system. I have thought of two ways to do this and was wandering your thoughts
Add a pipe between the boiler input and output just like most boiler temp return protection diagrams. I was thinking of using valves and adjusting the hot water manually that goes from the hot output and directly back into the return water into the boiler. This in my mind would keep my water in my boiler hotter and thus the pump would run more and put more heat into the house. My worries are that it would decrease my flow into the house and thus negate the idea
My other option is to add a blower (controlled by thermostat in house) instead of the little draft door that opens and closes by my thermostat. This would keep the fire rocking anytime the house is calling for heat and thus more heat than the rotating draft door.
I know I will burn more wood with a blower (and may have to reload during very cold nights) but this may be the simpler solution. Thanks for any input
 
I don't believe that installing a mixing valve on the return of your boiler will give you more btus. The purpose of a mixing valve is to protect the boiler from thermal shock. This occurs when metal is subjected to a sudden change in temp, and causes cracks. It will keep the internal temp of the boiler higher, which can help raise the temp of the fire within the boiler, which can give you better performance with a hotter fire. I wouldn't expect miracles though. Make sure that the wood you are burning is dry, this will be the best increase in performance.
 
i am by no means an expert on any of this but getting ready to plumb my boiler as well. possibly will run into this myself with my conventional boiler but what about the though of setting your low limit higher on the aquastat to allow the boiler to recover faster?
 
Have you tried setting your aquastat up to off at maybe 150? I don't think you'll get much heat at all out of baseboards below that, maybe even not a lot below 160. I think a 20 degree differential would be much preferred to the 50 degrees your set at. Also, I don't think there'd be much benefit in piping return protection, expecially if the manul doesn't spec it.

EDIT: Ooops, I should have read all of the reply above mine - already mentioned I guess.
 
Well The way that I have my aquastat wired is this. I do have a high and Lo setting BUT
The Lo setting I put at 170. This kicks the pump on when the water inside boiler reaches 170. The pump then runs until the temp drops back below 170 which can take a few minutes as it hold about 50 gallons of water. The high setting I have set at 190. If the water reaches 190 the aquastat keeps the pump running but CLOSES the draft door thus cooling the fire. It has worked well and actually i have never seen the water get hot enough to close the draft door (reach high limit)

When the pump kicks on and sends the hot water out of the boiler it is a pretty big temp swing from the water coming back in from sitting in the baseboards in the house. It can drop down to 120 or so if its not cycling much.
Thinking about the mixing valve setup my thinking is that it will keep a little hot water going into the boiler instead of totally depleting it thus keeping/getting the temp up quicker to 170 kicking the pump back on to send more heat. Its just a thought and I know there are other factors I have not thought of that could derail my thinking
 
Before I added my storage tank I had the same set up as you, only with oil burner instead of propane (moot point). I would start to circulate at 120F and it would just run and run and run until the fire burned out and the wood boiler cooled off to 120F and it would shut down. If I were you I would have the circulator come on at 120F when temperature rises and shut off at 120F when temperature is falling.

The idea is, assuming your propane isn't burning, since the only source of heat you have is from the wood, and you need every Btu you can get your hands on when heating, get that pump moving water so you can heat with it. So as soon as it hits 120F you can start circulating and start heating your house if it is calling for heat.

I do not have a boiler protection loop. I tried putting one in with a Danfoss thermic valve when I added the tank and ended up taking it out after much frustration with getting my system warmed up. The boiler is an old steel Memco that is nearly 40 years old. If it were cast iron I would put a protection loop in.

How long is your burn time? Without storage I had about 6-7 hours max to heat my house on one firing, depending on how cold it is outside. Storage has made my life much better, and my wife much happier.
 
Well my burn time at temps right now High 20's at night is 10-11 hrs. Of course if its colder that drops to 7-8.
I basically keep a fire all the time unlike gassers.
I did try what your saying at kicking on the pump at lower temp (cant remember what temp) and just letting it run basically continous but after several hours the house would start to cool and the boiler would be around 140 and not really gain heat as the fire continued to burn. It would not lose heat but remained constant at a temp that was not providing much heat. Basically as teh fire progressed and then started to settle down so would the water temp but it would not heat the house well Maybe I will try that again to be sure.
After thinking of what you told me about continous running of the pump I think maybe if I installed the blower instead of the closing flap that would probably work well. The blower may just be my best solution but just wandered what others thought. Would like to stay away from it just because I know I will burn more wood, little more electricity, something else to break, and it will run me about $250 to change to that
 
I have a similar setup to you - conventional boiler with no fan, just the draft door that opens & closes. It is a combo unit with an oil burner in the bottom. I also have times where if all the zones (4) open at once, the boiler temp will drop a lot. I put progammable stats in, and have them all set to first call for heat at varying times - ie, they set back during the day, and open an hour or so apart in the evening. If I'm home during the day, I'll keep a decent fire going & manually turn them up. I try to get it set so the draft door doesn't close until almost at 200 - the differential on that is 20, so it opens again when it gets below 180. Actually it might even be 15 so it reopens at 185. The circ stops running somewhere around 140 - and it starts as soon as it gets above that if there is a call for heat. But the thing that helped the most was getting the cold zones to stagger their openings.

When it was installed, there was a bypass loop put in with its own circ, but it only kicks in when the temp at the top of boiler gets above 190 or 195 - it circulates the water within the boiler so all the hot isn't at the top (un-stratification, I guess) - they said that was to prevent thermal shock. So if the top of boiler gets above 190 or 195, mine does mix some hot with the return if there is heat calling. Even with that, it will still drop way down if all zones open at once, so I'm not sure how much is actually bypassing, as both that circ and the zone circ are both pulling out of the same place at the top of the boiler - with the zone circ having a more straight up path, and more straight down path also on the return (the bypass loop is teed out and in from the side). Both pumps look the same, so I think their rates are the same - but not sure.

Not sure how much help that was...
 
Ahhh yes...I missed the comment about your draft. So do you have an arm that opens the draft that is set to close at a certain temperature? The Memco uses a 1/4-28 bolt as a jack screw to hold the draft door open. I don't have any experience with a fan/forced draft so I can't comment on that.

I understand where you're coming from...constantly wondering if you should open it up, burn more wood, and risk your house going to 80 degrees when you overtemp, or keeping it shut down to burn longer and risk creosote buildup and maybe not be able to recover if it gets cold and your house draws a lot of heat.

Sometimes it just comes down to messing with the system as a whole to figure it out. It took me a while to learn mine when I first installed it, then had to relearn when I added the storage tank. The payoff in the end is worth it though!
 
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