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[ptt811]

Mine was set on a 5 deq. diff when I got it and the fan shut off at 160....  After reading some here I changed it to a 15 deg. Diff and set the blower to shut off at 165. I think it does alot better job now.

[martyinmi]

Church,
   I'm surprised that you don't have water running out of your loading door all the time. 140* is way too low of temp to run an OWB at. There are those that will argue that is fine to run that low and that no adverse effects will occur where boiler longevity is concerned, and I suppose there isn't anything that can be said on this forum that will change their minds. I won't argue with them on this forum. I will simply state facts that engineers and technicians have relayed to me.
1. Boiler temps under 140 will cause premature failure of burn chambers(corrosion).

2. Boiler temps under 140 will cause premature failure of areas jacketing water(oxidation)

   There are 4 doors on my P&M Optimizer 250. 3 of the 4 will leak water(condensation) until the boiler temp is above 150*. My Empyre Pro 100 did the exact same thing, as well as the home built ones I've put together over the years. You will lose a little efficiency with higher temps, but you will gain longevity.
   My advise to everyone would be to call your manufacturers and see what they recommend, and follow what they say and keep accurate records along the way.
   There are at least 3 manufacturers now that I know of that recommend installing a mixing valve if your heat load is more than your boilers capability at times. The trend in factory preset temps appears to be higher than what it was even 1 year ago.
   I have over 10k into my boiler. I'm going to do everything in my power to make sure it lasts as long as possible. 

[church]

Thanks Martyinmi,
I have mentioned to others ( not here on the forum ) but those who ODW as well, ( networking ). And they were surprised at my temp setting as well. I just never readjusted it because it has been maintaining the house temp. I contacted the manufacturer as well and inquired their recommendation, they said they had one in use and it was running @ 130. Didn't mention anything in regards to raising it, just that if I had difficulty maintaining house temp, then to raise it to meet demands as needed. That it could be lowered in more moderate temps. Are you suggesting that I then should raise it at least 150* ? Still learning wth unit, didn't fire it after installed until Feb., this year. Ran it for couple of months using their stat setting @ 140*. Fired it this year around the first of Nov. It has really depended a lot on the weather as to how much h2o was on the door shelf. I have been playing with the blower, tryng to get it turned in if you will. I believe they have to much cfm for the unit, The stock blower was less in regards to their upgrade I went with. Like I said still following the leads found here applying what I feel what might be of advantage to efficiently operating it.
Thanks again for your feed back. Any other info would be appreciated.
Church

[martyinmi]

Between my sidearm for my dhw and my water/air exchanger in my furnace, I pull 20*-21* of heat out of my boiler water. Knowing that 20* are pulled out, I would never lower my temp off point to less than 154*. I don't ever want my water returning to the boiler under 150*.  I have my boiler set points at 195* off and 187* on and it works great for me. My furnace fan doesn't run near as much as it did when I kept my temps lower(165* off 154*on). The only thing I ever change anymore is the differential. Mine is a gasifier, and in order for proper gasification to be maintained, the refractory material has to stay hot, so I force it to cycle more frequently when the weather is warmer. If I know that I am going to encounter a few 50* days, I will go to 195* off/ 191 on. This ensures that gasification will take place almost instantly, and it insures a clean, smoke free burn. I have no way of knowing for sure, but my wood consumption doesn't appear to go up with higher set points, and my electricity usage definitely goes down. The higher temps also fool my water heater in to thinking that it's bigger than it is.
   I think you need to follow your manufacturers recommendations for your boiler. It's not my place, nor anyone else, to give you advise that is contrary to what they tell you either in print or by phone. The only advise I might throw out there would be to have them put in writing that running your set points that low won't void your warranty.
   Marty

What brand and size is your boiler?

[Sconnieman]

1)Everyone always talks about measuring return heat why is it important for the temp returning not to be to low?

2) why use a heat exchanger in domestic hot water........why not just use the water out of the OWB tank and plumb the local well up to refill the OWB when water is used out of the OWB tank? My domestic hot water tank is only 80 gallons ........the OWB is 750 gallons

Thank for entertaining the silly questions of a newbie

Higgins,

Don't worry about the "silly questions" everyone has to learn about this stuff when they first get started.

1) I see two reasons why you want to be concerned with return water temperature. 1st and most important to me is wood usage. The way I see it is that my goal is to keep my water at 180 degrees. If I do that then my house is warm and my domestic hot water is hot. So the way I keep my water hot is by burning wood, when the water temperature drops, my draft fans kick on and burn my wood hotter (faster) to get my water back to 180. The less that happens the less wood I burn. The 2nd reason would be the condensation issue that everyone else is talking about, but really that is secondary because if you set your aquastat temp high enough and you keep wood in your stove you won't drop that far in temperature too often.

2) As far as I know no one does this. The main reason is just about everybody treats their boiler water with chemicals to remove corrosive elements from the water. Some people put anti-freeze chemicals in their water to reduce the chance of their pipes freezing due to a malfunction. Bottom line is that the water that is cycling through your boiler would not be considered safe for human consumption. Also it would cause you to burn more wood due to what I talked about in my answer to your first question.

Hope that helps,
Andy

[RSI]

I would suggest you turn the temperature up to 180 and then lower it over time. This will allow you to see how much difference it makes on wood and how clean it runs.

You don't want to get the boiler water temperature under 140 but i am not sure why the return temperature is that big of a deal. If you have 180 degree water in the boiler and the return is 135 it means you have a very low flow rate and the water will mix in the boiler.

Can anyone confirm that the bypass valves do actually go off the return temperature? I would have guessed they see the supply and cut it off when that gets too low.

[willieG]

temps in the return are a big deal (or can be as i stated before) 180 in and 130 out suggests low flow..so say this is happening when the outside temps  are nice winter days (20 or so degrees) and your house is staying at your set temps...when the outside air gets to one of those cold -5 or -10 degrees i would be willing to bet that that low flow that was causing your low return temps will now not be able to meet your homes demand for higher btu. btu delivered to the house are directly related to GPM and water temps, the more GPM the higher the return temps. the way your btus are transfered to the home is by the size of your heat exchangers or feet of rads or feet of lines in your radiant heat sytstem

lets say your home is needing 50,000 btu per hour to heat on a cold night, that means you would need at least 5 gpm at 180 to deliver that amount, your return temps may be (again not a true amount) lets say 130 and just barley heating your home. that same water at 180 and only going 2 gpm would only deliver 20,000 btu per hour and would not heat your home and the return temps would be a lot lower. on the other hand ,again, if you were delivering 10 gpm you would have available 100,000 btu per hour and only needing 50,000 your return water would be much higher...so i guess one thing you could say is the higher the return water temps  give you a "cushion" that you can survive those - 40 nights, they may not be often but they do happen

[RSI]

It also depends on how often the blower runs. If it is a low return temp but the blower only runs 10% of the time it will just run longer when it is colder.

[mcarter]

Ridgekid, any idea what your rate of flow is in GPM?

Your monitoring system is quite spectacular, I've seen your graphs.  It would be neat to take that a step further with a programmable microcontroller and be able to do things like increase/decrease GPM flow based on return temps, etc... Of course that would require a pump that could be set electronically instead of manually. 

I still follow what someone posted months ago on another post, "why take something that is simple and make it complex."  Or something to that effect.  Still, something like that would be cool to compare to a standard install.  And compare too, if the added cost would even be worth the benefit.

[Ridgekid]

I have a TACO 009-F5. According to my pump flow chart it states:

Flow Rates at common equivalent Lengths:
(Assuming they mean one way-Someone can correct me)
Using 1" PEX
N/A GPM at 50' (Overloaded)
7.79 GPM @ 100'
7.34  GPM @ 150'
6.96 GPM @ 200'
6.63 GPM @ 250'
6.34 GPM @ 300'

I'm at 115' at furthest point, so I assume I'm running around 7.6 GPM?

I scan where I got the info and email it in PDF. Send your request through Ridgekid@msn.com

[RSI]

Where did you get that chart? You most likely have to use the entire length round trip. You also need to make sure it is for pex and not copper.
The heat exchangers and elbows will slow it down also.

Do you have sensors on all 4 ports of the plate heat exchanger? If you do, you could get a pretty good estimate of your flow rate by running a hot faucet and measure the gallons per minute that it is putting out. Then using the temperature differences can calculate the flow rate.

[rosewood]

lower water return temps at wood furnace is not such a concern,the big concern is if you have a boiler in your house that your wood furnace is maintaining hot water for. undersized hx and incorrect pump flow can cause your indoor boiler too be shocked and crack its water jacket. this is caused when multiple zones are in use and boiler supply of hot water is low returning cold water back to boiler.

[Ridgekid]

RSI. Got that info out of book supplied by CB.  Hydronic component sizing.

[martyinmi]

lower water return temps at wood furnace is not such a concern,the big concern is if you have a boiler in your house that your wood furnace is maintaining hot water for. undersized hx and incorrect pump flow can cause your indoor boiler too be shocked and crack its water jacket. this is caused when multiple zones are in use and boiler supply of hot water is low returning cold water back to boiler.

You touched on a subject that I wasn't going to comment on when you mentioned the word "shocked", but, hey, you sorta' brought it up, so here's my comment. The guys that I've spoken to about boiler longevity also talked about what differentials should be to get the longest life possible from your OWB. In a nutshell, the shorter, the better. Metal that has more frequent small expansions/ contractions will last longer than metal that has fewer large expansions/ contractions. In other words, keeping your boiler at a more steady temperature promotes longevity. Shocking your boiler by allowing it to cool down substantially and heat back up is harder on it, as the metal expands and contracts further. I used to run one of my homemade ones with a 20* differential, and when it finished cycling, it would make a few creaking noises nearly every time. I've never tried it on my Empyre or my P&M, so I don't know if they would like it or not. One guy said never run more than a 15* diff, the other said 20*, but they both said that less was more in the long run. I'm not sure I buy into their thinking altogether, but it does make some sense. I think that a 10* diff will be the most I run in the future.

[Ridgekid]

Where did you get that chart? You most likely have to use the entire length round trip. You also need to make sure it is for pex and not copper.
The heat exchangers and elbows will slow it down also.

Do you have sensors on all 4 ports of the plate heat exchanger? If you do, you could get a pretty good estimate of your flow rate by running a hot faucet and measure the gallons per minute that it is putting out. Then using the temperature differences can calculate the flow rate.

Yes pex lines not copper.

Yes on both hx'ers.