# Outdoor reset, and how low a temp can I operate a Burnham V8 cast iron oil boiler without condensati



## velvetfoot (Dec 18, 2009)

I know this is a wood forum, but I haven't been able to find a source for the info anywhere else yet.

I have a Tekmar 250 outdoor reset control coming in the mail.
One of the settings is 'minimum boiler temperature', and the odr manual says 'consult mfr'.
Of course, Burnahm won't talk to a mere homeowner and the 7 heating co.s that I called were all out on jobs.
Who knows how technical they can or want to get in talking to me.
But that's a side story.

Besides just setting the minimum temperature for the odr control, I'm thinking I could tweak the settings on the outdoor reset so that the boiler operates generally at lower temps, except for the separate zone for dhw (cold start boiler), which is also on priority.  The insert heats the downstairs quite well, so the boiler is, in effect, oversized by 2 (already have a smaller nozzle).  I'm thinking lower water temps going through the fin and tube baseboard convectors could not only allow savings with lower temps but maybe longer run cycles.  The Tekmar manual says normal range of operation of fin/tube baseboard is 140-180F, but how low can I go without damaging the stack or boiler.   How could I even tell?  Water under the boiler?  I figure the domestic hot water loop coming up to 180F periodically would mitigate some.  I'm pretty sure the stack itself is stainless, but the connection is galvanized.

Could I go to 130F?  Lower?


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## ISeeDeadBTUs (Dec 18, 2009)

I likewise have a Tekmar on my Viessmann. The fact that the Company you buy their sheetz from wont talk to you is typical . . .though ridiculous. You may find, as I have, that the installer is almost no help. They go with factory settings and walk away.

I have messed with the slope and shift quite a bit, and I think I have it where it works the best for me. Sometimes in the spring I will tweak it a bit. Of course, the whole concept of the outside control is to minimize  supply temps as it gets warmer outside. But since I am heating the boiler with an external source, I'm not as concerned with limiting supply temps as I would be otherwise.

Have you tried http://www.heatinghelp.com/  ??

Jimbo


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## velvetfoot (Dec 18, 2009)

Thanks Jimbo.  
I'll try that link.


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## velvetfoot (Dec 18, 2009)

That's a pretty good site. 
Lots of info.  Not sure totally how it works yet, but again, a search yielded a lot of stuff.
Thanks again.


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## DaveBP (Dec 18, 2009)

Have you looked through here yet?

http://www.tekmarcontrols.com/literature.html


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## Chris S (Dec 19, 2009)

Generally with cast iron you want 140 degree return water to prevent condensation,  I believe you'll find that information in the Burnham manual.  Buderus has "special"
cast iron so they can go lower.
Hope this helps


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## velvetfoot (Dec 19, 2009)

Thanks.  No, nothing I could find in the Burnham manual:
http://www.burnham.com/pdf/V8H_io.pdf (a later model than mine, but appears to be close except for controls.)

I've heard about the "special" cast iron.


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## OldDedHed (Dec 19, 2009)

I have a Tekmar 256 on my corn/pellet/multi-fuel boiler and there are default settings for boiler minimum depending upon your end delivery device (fin tube, radiator, radiant, etc.). Chris is correct when he says 140 is a popular number for boilers to prevent condensation. I see from your postings on the other forums that you have fin tubes on your system. The default for those on the 256 is 140, and I'd go with that to ensure that you get adequate heat in the house AND prevent condensation in the boiler. Explains why most installers go with the defaults and walk away


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## velvetfoot (Dec 19, 2009)

Thanks.  My idea is that because the boiler will be oversized when the insert is running.  If the boiler is running cooler it would run longer on each cycle, no?  Both would lead to more efficiency.  I just don't want to go too cold.

Whatever settings, are you happy with the Tekmar 256?  It seems flexible and capable and reasonably priced.  
It should get here tomorrow.  I'm psyched (believe it or not).


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## OldDedHed (Dec 19, 2009)

I'm still tweaking it, but it seems that it will be a good thing in the long run. The challenge for me is not knowing what parameters were used when my heating system was installed. So there's been some trial and error with boiler design, outdoor minimum, and other settings. I had the boiler design temp set at the default (180) and with the recent single digit temps the house never made it to 68 °F . My second floor has electric heat that is basically not used so that throws the curve off. I had to jack the boiler design temp up to change the curve and bring water temps up. The other thing that will complicate is the other heat source you're using. I think you're right, though, you should be able to run the boiler cooler because the insert will be carrying some of the load. I started low and worked up from there, and also made sure my zones were tuned to the 20 °F  drop that is supposed to be there for fin tube installations.


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## velvetfoot (Dec 19, 2009)

It sounds like you're in the opposite situation than I am with no heat on second floor.
Maybe the radiators just don't have enough "oomph".
Is phase two running pipe upstairs? This stuff could get to be an expensive "hobby".

I've been reading and trying to understand the manual. It would seem (this is from a newb) you could bring the outdoor design temp in and that would steepen the curve.  If the boiler temp is indeed at the design max then maybe you can't get any more heat out of it through the existing terminal units (I just picked up that expression!). 

I think my situation is close to "short cycling".


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## OldDedHed (Dec 19, 2009)

Yeah, heat to the second floor is a project on the list. Have to pay for grad school first. It is funny how buying a corn boiler got me into home heating as a hobby. I raised the boiler design temp to 195 and life got a whole lot better, so you're right about the curve.

Short cycling is taken care of by the differential setting. If I remember the manual right, they talk about leaving the differential on automatic to prevent short cycling. I couldn't do that because the corn boiler does make heat as fast as an oil boiler does. The auto setting will probably do the trick for you. Good luck with the install!


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## velvetfoot (Dec 20, 2009)

You're right about the differential being key.  I'm sure there'll be no end to the tweaking.
I was surprised at how big the outdoor sensor unit was.


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## velvetfoot (Dec 22, 2009)

Well. I just installed it and didn't burn anything up.
It's way cool.  I should have run some long wires upstairs to see what's going on from the couch instead of running downstairs every time the burner turns on.
I have it set on the defaults except lowered the design temp 5 degrees.  That flattened the curve some and depressed the boiler target temp.
I'm not totally certain on how the differential works though.  It went way over the target, which is good since that's kind of what I'm looking for.
Not sure what "heat load" is?  Outdoor temp?


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## velvetfoot (Dec 23, 2009)

Well I'm getting exercise going up and down the stairs anyway.
I've moved the design outside temp to -10F, everything else default for fin/tube (180 boiler max, 140 boiler min, etc).  Auto differential is on.  The last cycle I got was 9 degrees below and 6 degrees above the boiler target of 156.
This is heating only top floor, with insert assuming the downstairs work.  

Anyway, it seems like it has a lot of potential, as long as I don't mess anything up or slip on the stairs while racing down.
Those fancy systems the wood boiler people are using is appealing:  point, click.


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## velvetfoot (Dec 23, 2009)

Well the upstairs hasn't gotten up to the thermostat setting at 12F outside.
Hey, it's probably saving energy...


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## heaterman (Dec 23, 2009)

A V-8 will tolerate down to 135-140 while firing. If you get creative you can let the water temp drop to 110 or so by rigging a couple relays to keep the burner off while the pumps are running, then kill the circulation while the boiler temp comes back up to normal operating range. Viessmann and Buderus run their oil products like that all the time when using their controls.

Caveat....unless you are willing to void your warranty and have a good knowledge of hydronic controls, I have to say just leave it at 140. You may lose a couple percent efficiency but your boiler will live a longer and less complex life. 

The only oil boiler I know of that will actually fire into 100* water temp is the Viessmann Vitola VB-2. But then you're talking an $8,000 boiler/control package so it should do something out of the ordinary for that price.


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## velvetfoot (Dec 23, 2009)

Thanks very much.  
Would you be able to answer just one more question?

I have the 256 installed, but I probably should have gotten the more expensive 260 model (but it was 200 bucks more!) to control the domestic hot water.
Will I have to rig up another separate relay?
It's working well now, but maybe when the weather gets warm, there won't be as much dhw?

Thanks again.


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## velvetfoot (Dec 24, 2009)

I think I figured it out (seems to work anyway).
The boiler zone controller is an Argo ARM-4P.
It has priority for domestic hot water.
I jumpered the dwh tank aquastat connections on the Argo to the boiler wires on the Tekmar.
Two sources of voltage coming together.  Was careful of phasing.
Seems to work.  No smoke!
When there is demand for dhw, the priority light goes on, other zones drop out, and aquastat trips boiler when high limit achieved, even after the Tekmar would have shut down the boiler.


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## velvetfoot (Dec 30, 2009)

It turns out that solution didn't work.
A call for heat from a thermostat backfed the Argo and triggered the priority dhw zone.
I wound up getting a Tekmar 24 volt Relay 003 (much thanks to people at doityourself.com) .
It fires up the dhw zone in parallel to the Argo, but the relay separates the two sources of voltage.
So, when the dhw circulator is running, the boiler goes to the higher temperature of its aquastat, rather than what the Tekmar is targeting.
The $40 (delivered) wasn't a bad deal.


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## velvetfoot (Sep 17, 2010)

It's that time of year again, and I'm thinking of heating stuff again.  Here is a picture of the setup as I promised in another thread last year.
Again, the advantage is that dhw priority still works and uses the usually higher temp of the boiler aquastat.


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## btuser (Sep 17, 2010)

I think you're right where you want to be with your settings of 140f minimum 180 max and auto dif.  You're design temp is pretty low at -10, which will effect the curve but I set my Tekmar 260 up the same way, and felt it helped with a faster recovery when needed.  

There are two things to consider when talking about return temps:  The first one is condensation and the second one is thermal shock.  The "special" cast iron that Buderus uses is called G20, and is impregnated with silicone to make it more elastic.  This allows lower return temperatures but doesn't help against condensation.  What will happen is the cooler water will enter and hit a wall of the combustion chamber, and that's where you'll get your condensation.  The Buderus 215 and the improved G series fix this by injecting the return water further into the boiler.  The new Burnham MPO has a special fitting for this.  The older V7 and V8 do not, hence the need for a higher return temp.  You'll notice if its happening if certain areas of the casting gets a build up, and that little bit of soot is a great insulator that continues to grow like fungus.

140 is good, plus if you've got baseboard you really need 130+ or there's very little heat output because the convection doesn't happen.


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## btuser (Sep 17, 2010)

I think you're right where you want to be with your settings of 140f minimum 180 max and auto dif.  You're design temp is pretty low at -10, which will effect the curve but I set my Tekmar 260 up the same way, and felt it helped with a faster recovery when needed.  

There are two things to consider when talking about return temps:  The first one is condensation and the second one is thermal shock.  The "special" cast iron that Buderus uses is called G20, and is impregnated with silicone to make it more elastic.  This allows lower return temperatures but doesn't help against condensation.  What will happen is the cooler water will enter and hit a wall of the combustion chamber, and that's where you'll get your condensation.  The Buderus 215 and the improved G series fix this by injecting the return water further into the boiler.  The new Burnham MPO has a special fitting for this.  The older V7 and V8 do not, hence the need for a higher return temp.  You'll notice if its happening if certain areas of the casting gets a build up, and that little bit of soot is a great insulator that continues to grow like fungus.

140 is good, plus if you've got baseboard you really need 130+ or there's very little heat output because the convection doesn't happen.  I'm guessing I saved about 150 gallons from the OTR.  This year I'll be counting on The Viessmann KW10 control, which isn't a learning curve.  I may end up re-installing the Tekmar but I'll give this a shot first.


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