Controlling return temp


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Old 11-08-06, 08:02 AM
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Question Controlling return temp

I know there is a way to control it with mixing valve for example etc, but why some manufact. do not have any provisions/mention it in their manuals? How important is it? I have Buderus boiler( cast iron) and in my manual there is no return temp requirements for low volume systems, <115 gal. How many of you control your return temp? I guess it only applies to boilers with set low limit (not for cold start boilers)

Below is Buderus manual link

Can somebody explain me table 3.2.1 please?
They specify min boiler temp, 150", I doesn't make any sense as they control it with 8148 (cols start stat), see page 51. Boiler can cut off at 130 as long as thermostat satisfied when used as a cold start?
Also in the same table they stating mixing valve is necessary (for aquastat applications). Is it only for low temp circuits? At the same time column 4 says that return requirement is only for large systems?
Do I need to maintain return temp or not? If yes, would indirect zone by itself sufficient enough to maintain proper return temp?
http://www.buderus.net/Portals/16/Final%20Version%20G115%20(new)%20Installation%20Manual%20062204%2063030586.pdf
 
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Old 11-08-06, 08:58 AM
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Return Temp

Return temperature is not the issue with low volume systems it is with systems using cast iron rads or low temp radiant, but it always desireable. This is something fairly easy to do with a thermostatic by pass valve. Also be sure to see footnote #3.
 
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Old 11-08-06, 11:18 AM
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Originally Posted by Grady
Return temperature is not the issue with low volume systems it is with systems using cast iron rads or low temp radiant, but it always desireable. This is something fairly easy to do with a thermostatic by pass valve. Also be sure to see footnote #3.
Basically they tell me to achieve 150' within 10 min and maintain it. I guess it's impossible with cold start setup, unless you have a bypass? Did I get it right? Do you think I can avoid bypass installation once I have my indirect installed? I think I can get 150' at the boiler when indirect will call for 140' for DHW.
Right now, with indirect being disconnected, Thermostat setting at 69' and lowest outside temp. 39-40 at night 59-64 during the day my boiler goes up to only like 100-150 to satisfy the thermostat. My high limit setting is 180 with 20' diff. I tried to have it with low limit set to 130 with 15' diff and I think that's no good. With low limit on, my boiler goes up to 130, circ. kicks in and temp drops as low as 95-98 with return rushing into it.
I don't think it's good for cast iron boiler. So I set it for cold start, at least for now/these mild outside temps.
What do you guys think?
 
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Old 11-08-06, 11:27 AM
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Looks like they really want you to have the 2107 (and no, I'm not trying to beat the dead horse.... ). They don't trust aquastats so the keep the min temp high, and they want you to somehow cycle the thing every couple hours. If you go with the bypass, use a Danfoss Thermic 3-way valve. That was suggested to me by several people back when I had a standard CI boiler. http://www.danfossheating.com/products/pdf/TV_%20thermic%20valve.pdf Technically, they want a motorized valve though....

And now to beat the dead horse. Sorry. Think for a minute about the long-term implications of fuel use and supply temps by doing what they want with a bypass setup and perhaps not having a cold-start system. In a couple seasons, tops, you will have spent in fuel and decreased efficiency what the 2107 cost. And maybe you spend a hundred or two to get the bypass right. You're right up there with the cost ($750?) of the 2107, and eventually you're beyond it.

I've only been doing outdoor reset for about a month, but man I'm a convert. Low supply temps rule. The automation of the whole thing rocks.

Check your PM. I have a suggestion.
 

Last edited by xiphias; 11-08-06 at 11:47 AM.
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Old 11-08-06, 01:19 PM
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I actually gave up on 2107 and got AQ475A1004 http://www.energysavingsusa.net/page/page/1647563.htm

You should hear what one supplier from PA told me
"we don't sell it to private parties due to liability. What if you get electrocuted installing it or something? But we do install them ourselves, just not in your area"
I guess If I sued the hardware store every time I hit my thumb with a hammer, I would be very rich. What a lame excuse
 
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Old 11-08-06, 05:14 PM
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That'll do just fine.
 
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Old 11-08-06, 08:28 PM
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Originally Posted by radioconnection
I'm in the same boat with a Biasi B10-4. Three zones of various sizes, and the largest uses CI baseboard. I have a Tekmar 260 outdoor reset, but I don't see how it works to solve the return temperature minimum. In fact, with the Tekmar, the circulators run on a heat call on a cold boiler. Even more confusing is the minimum delta T spread between supply and return?

Pete
Pete,

I'm not sure what area you are from but anyways,
with mild outside temps this time of the year (NJ, 37-49' at night,
59-70 day) how hot does your Biasi get on average to satisfy thermostat for one cycle? I just think anything below 130-140' is
certain way to create pitting and condensation.
As far as low return temps go, do you guys think Indirect zone should take care some of it or should I think about balancing valve?
 
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Old 11-09-06, 08:25 AM
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Let me try to inject what I know about return temps and all that jazz.

First, for a cast iron (CI boiler), return temps need to be above 130F for gas, and IIRC above about 115F for oil (might actually be 105F, don't remember). The two different fuels have different condensation temps. What you are trying to avoid is prolonged condensation inside the boiler. That is not good for cast iron. Think acid rain inside the boiler.

The idea with cold start boilers is that yes, you are well below condensing temps during start-up, but once you get going, you are well above condensing temps so the condensation is evaporated, i.e., you are going minutes, not hours or days, at condensing temps. A real condensing boiler seeing return temps below the condensation temp for long periods can produce several _gallons_ of condensate per day. Obviously, you do NOT want that going on in a standard CI boiler.

A typical space heating circuit is designed around a 20F deltaT. Water going out at 180F should ideally give up its BTUs and come back at 160F. Hardly ever happens in reality. For my two zones, I probably get 10F on one, and 15F on the other.

In the absence of primary-secondary piping, or a bypass (motorized or thermic) loop, the return temp into the boiler is what it is. There is no way to regulate it. If you send out 140F water on a circuit with a 20F deltaT, it will come back at 120F. If you do that on a gas-fired CI boiler for days/months/years, then you will condense and corrode out the boiler because 120F is less than the condensing temp of 130F. (But you'd be OK with oil.)

What the various reset controls do is simply control the supply temp. The tekmar 260, for example, cares only about what temp it sends out to the heating circuits. For a CI boiler, it relies on YOU to make sure that if you need boiler condensation protection, you provide it by p/s piping, a thermal or motorized bypass, or a minimum supply temp that yields a return temp >=130F.

An example that I'm quite familiar with is how the Burnham Revolution works. It has an internal circulator (a 007) on an internal primary loop that varies its speed to both inject to the required water temp called for by the tekmar 260 (which monitors supply temps on the secondary loop -- i.e., the supply header), and protects the boiler by mixing the cold return water with the hot internal water to keep the heat exchanger at >130F. There's a control (vs3000 -- built by tekmar for Burnham, IIRC) that monitors the various temps and controls the pump speed. Essentially, p/s piping with injection mixing inside the boiler.

Soooo, with something like a gas-fired Biasi and a standard piping setup, the best you can do will be to set the minimum supply temp to whatever you can get away with that results in ~130-140F water coming back into the boiler. To do this, measure your deltaT at various operating conditions and make sure you don't spend a lot of time below 130F return temps. If you have a 10F deltaT, you could go down to 140F supply. If a 20F deltaT, then 150F.

Officially, this would be known as "partial outdoor reset" because there's a lot of outside temp that could be satisfied by <130F supply water, but you can't go there because the return temp would be too low. Stay there for days/months and the boiler will rot.

Example. In my climate with long shoulder seasons, partial outdoor reset wouldn't make much sense. I can go half to two-thirds of the entire heating season with supply temps <130F. So far this fall I've been doing 125F or less, with a "spike" to ~135F during a recent cold spell. If I was constrained to 140-150F supply, that's not really efficient for more than half the heating season.

A bypass will not help in this situation. If the water coming out of the boiler is <130F, there's no way to warm it up before it goes back.....

With a CI boiler, the way to achieve full outdoor reset in the heating circuits is to pipe p/s. The primary loop runs hot to protect the boiler, and the heating circuits get the required supply temp by 3-way or 4-way mixing, or variable speed injection pump. There's two technical essays at tekmar on all this. I had to read them 10 times to get it as I've worked up the learning curve, but it's worth reading.

http://www.tekmarcontrols.com/literature/acrobat/e002.pdf

http://www.tekmarcontrols.com/literature/acrobat/e021.pdf

And you can pipe the indirect right off the primary loop to take advantage of all that hot water and bypass (as it were...), the injection system for the space heating circuits.

p/s piping is pretty simple. There are a few requirements for flow rates, tee spacing and whatnot, but it's pretty straightforward. Dan Holohan has a book called Primary/Secondary Piping Made Easy. The tekmar literature shows design criteria and formulas for sizing. So does the Taco Radiant Made Easy Guide.

I chose the easy way out and went with a Revolution with all the p/s stuff built in because I didn't go with a mod/con. It's all in the box, so to speak.

Ok, that's the heating brain dump for this coffee break. Tired fingers!
 
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Old 11-09-06, 01:40 PM
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Wow xiphias, thanks for detailed explanation, I seriously considering p/s setup.
But I still have one thing unclear, what do they min by boiler min temp 150' in that Buderus manual? table 3.2.1 I completely understand note 3, they want 150 to be min high limit and they want me to maintain this temp. Ok, It's kind of confusing. Buderus specifically states 8148 as alternative to 2107 or 2109
Unfortunately 8148 does not have built-in pump logic to prevent condensation.( I with 2107 or 2109 would explain how this pump logic works.) so let's say it's 60' outside and 66' inside. My thermostat would like to achieve 69. Being that 8148 cold start stat, zone circ comes on with the boiler. At about 100' boiler temp thermostat satisfied, system shuts off. 150' not achieved, boiler operation conditions were not met.
Adjusting Low limit with for example 7224 isn't gonna help as as soon as low limit met ( I guess Buderus desires it to be 150? )
zone circulator starts and injects cool water from return. This scenario is even worse. I guess the only way out of it is to have
p/s setup, right?
As many Buderus G115 system installs I've seen installed (Pro install pics on the web) I have never seen p/s setup. Even the boiler manual, the only provision it has is fig.44, boiler bypass for large, 115 gal. water system.
i wish I could post some questions for Joe@Buderus on oil tech talk forum but admin there ignoring my requests to join for some reason

Here is my boiler manual for any references
http://www.buderus.net/Portals/16/Final%20Version%20G115%20(new)%20Installation%20Manual%20062204%2063030586.pdf
 
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Old 11-09-06, 02:07 PM
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Let me ponder this stuff and get back to you guys. I think we're all looking for the right answer.

I'd be willing to be that 99% of those pro install pics show your boiler with the 2107. They sell the customer the boiler and control package, pipe it right, and let the 2107 do the rest.

zaq, check your private messages. I have some stuff for you.
 
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Old 11-09-06, 02:39 PM
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True, most of those installs have Logamatic.
I'm sure one of the reasons that 3.2.1 table in the manual is so strict toward 2109 or aquastat cuz buderus wants you to get 2017.
What can 2107 do that my Honeywell AQ475A aquatrol with taco SR503 and L7224U stat can't do?
Buderus simply has a supply and a return, that's it. There is nothing like in Revolution boilers. No matter would it be 2017 or 2019 or 8148, there is no way to get the effect of a mixing valve or regulate return temp. The only way to to that is to have the boiler system build this way, with p/s, mixing valve etc. How in the world with 2107 there is no requirement and with 2109 or 8148 it is necessary? that table makes no sense However, I guess I'm a noob and don't know a lot about this stuff
 
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Old 11-09-06, 02:49 PM
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Originally Posted by radioconnection
Maybe I'm misreading it, but I read it as 150 degrees F being the the minimum permissible setting for the high limit aquastat. I don't see where it says to maintain 150 degrees as the minimum temperature? In practice, I'd think most hi-limit aquastats would be set in the area of 180 degrees?? Grady? Any input here?

Pete
True, but if you read that not 3 right below that table, they want me to achieve this temp of 150' in 10 minutes and maintain it during boiler operation. To me it sounds like they want me to have my boiler run at nothing less than 150 every time it starts up.
 
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Old 11-09-06, 04:19 PM
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xiphias,
I emailed Joe, so hopefully he can clarify few thing for us.
I'll keep you guys updated.
 
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Old 11-09-06, 06:52 PM
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zaq, I don't get it. I've read through all the literature on the 2107 to see what the magic might be. There is mention all through the application guide about condensate protection. There is mention on the spec sheet about boiler protection logic (item 4). They have something somewhere about "Pump Logic." But all the piping diagrams show plain vanilla piping arrangements. Only thing I can think of, and it would be elaborate and against what I know about flow rates in space heating, is that somehow the 2107 talks to the pumps and regulates flow until the boiler internal temp is where they want it, then it ups the space heating flow as it's able. I view that as a total longshot and highly, highly improbable. Among other things, it would require a pump(s) rated for variable speeds and a set of voltage regulators to do it. Highly, highly unlikely all that is in the 2107.

That, or with the relatively high water content (8+ gal) of the boiler, the 2107 fires the boiler and heats the water a bit before energizing the circs. With that kind of water volume, maybe you can do that. Well beyond anything I know, though.

Something else is up here. I hope you get a response from Joe. I'd be interested to hear.

My gut feeling is that if you figure out the right min return temp to avoid condensing with oil (105 or 115?????), you can probably do a more aggressive partial outdoor reset than with a gas boiler and not have any problems.

All that said, however, the 2107 is a pretty impressive control and its no wonder it costs so much. It would be roughly equivalent to a tekmar House Control, which runs about $1k.

But the 2107 would allow you to do away with room thermostats and just use their BFU's or whatever. The 2107 does the rest. Pretty neat if you're really into "comfort systems." Me, I have two cheapie Lux stats that cost $9 each (after a local gas co rebate...) talking to my tekmar.

But I think my reading shores up the impression that what the pros are doing is selling the boiler and 2107 as a package that really makes their lives easy. All factory stuff, one shade of blue, put it all together following the directions and you're done. Anything goes wrong and it's on Buderus (and if you're a pro hope that they compensate adequately for warranty work). It's a no-brainer for them, and it's a heck of a good system.
 
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Old 11-09-06, 07:01 PM
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Pete, I'll take the above as compliments. It took months of reading and research learning about all this. Motivated by a totally unacceptable and ultimately hazardous heating system. I had one shot to get my new install as right as I could this time around, having been totally hoodwinked only three years ago due to a misplaced faith that somebody with a professional license actually knew what they were doing. In my case, getting (over)educated for this go-round saved and will continue to save me a lot of money. Took a whole lot of time, but I think worth it.

One of the reasons I continue to hang out here is to help out, sharing what I've accumulated in the old acorn. This site (Grady especially) helped immensely.

Plus now I'm a hydronics wannabe.
 
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Old 11-10-06, 07:30 AM
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Everything you wanted to know about flue gas condensation:

http://www.pubs.bnl.gov/documents/28709.pdf

The upshot is that the condensation temp for gas is 130F, and for oil about 115F.
 
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Old 11-10-06, 02:24 PM
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flue gas temps...

Thanks Xiphias.. I'm still getting confused about the flue gas temperatures. I'll have to read some more and see if I can figure it out.
 

Last edited by radioconnection; 11-10-06 at 09:09 PM.
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Old 11-10-06, 03:53 PM
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Question

Originally Posted by xiphias
If you go with the bypass, use a Danfoss Thermic 3-way valve.
Anyone have any leads as to where these can be purchased ? I can't seem to find a distributor! ...

TERMOVAR seems to be another very similar product.

Thanks!
JB
 
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Old 11-10-06, 04:16 PM
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Danfoss

Originally Posted by NJ Trooper
Anyone have any leads as to where these can be purchased ? I can't seem to find a distributor! ...

TERMOVAR seems to be another very similar product.

Thanks!
JB
Not sure if they are in your area, but Litco Supply is a Danfoss distributor covering parts of New England and New York..

Pete
 
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Old 11-10-06, 06:41 PM
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Thermostatic by-pass

R.E. Michels carries the Danfoss. They have stores in Absecon, Pennsauken, Piscataway, Trenton, & Vineland.
 
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Old 11-11-06, 09:11 PM
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Thanks guys...

I did find them also at Patriot Supply this afternoon!
(Danfoss 065B-8923 is the 1" Return line model, 140*F)

and they also show the Termovar valves as available through ENERJEE, but Enerjee's website seems defunct (domain name for sale) comparable prices, but only available in 1.25 and 1.5 inch models.

(Patriot also has some pretty good deals in their ebay store!)

C/YA!
JB
 
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Old 11-14-06, 06:56 PM
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Joe's answer

"The requirements for the G115 are as follows:

If using a standard cold start type of aquastat in a conventional
baseboard type of system, the high limit of the aquastat must be set at
least at 150 degree's. This would permit the boiler to heat enough to
dry out any condensation that may have formed inside the boiler.
In a large mass system, >115 gals/100,000 (large, older cast iron
radiators) a by-pass, mixing valve or low limit control is required to
prevent prolonged cool return water temperatures causing condensing
inside the boiler. With this type of system a minimum boiler temperature
of 130 degrees is required.

When using the G115 in a radiant floor application with design
temperatures above 130 degree supply/113 degree return, then no by pass
is required. We suggest a mixing valve for the radiant be used in any
low temperature application."

OK,
I have 74' of Base-Ray CI baseboards in my place:
22 gal of water,
~31kBTUH at 4 GPH and 150F
~46kBTUH at 4 GPH and 180F
Let's say I have 100' of 1" L pipe ~ 4.074 gal (I have mixed 1" and 3/4" and less than 100')
Boiler-8.7 gal
Total water content: 34.8~35gal

I think I will be ok without by-pass.
I'll install my outdoor reset and see if anything will change with this mild temps warm ups

BTW, do you guys think it would be a problem?
I got my exp. tank based on Amtrol manual for CI baseboard application, #60 tank.
I just checked Amtrol site and they also have a table for tank sizing based on the water content. It looks like #30 is my size.
Do you think #60 will be ok?
 
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Old 11-14-06, 07:09 PM
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Well, as it's sometimes said by captains for hire, "I ain't got a dime in her."

Sounds like you can go for it and get a pretty good range of reset. Just keep checking up on the temps.

I don't know about expansion tank sizing. I would assume that bigger is not necessarily a problem, but would right-size over over-size.
 
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Old 11-14-06, 07:10 PM
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I guess there is nothing I can do about the boiler cutting off below min temp. in these seasonal mild temperatures. I checked inside my boiler and signs of condensation are obvious.
 
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Old 11-14-06, 07:21 PM
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Get this. Think on it over the winter and maybe go for it next summer:

http://www.heatinghelp.com/shopcart/product.cfm?category=2-44
 
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Old 11-14-06, 08:08 PM
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Just a thought. Could it (rapid boiler cooling) be caused by oversized GPH circulator?
I just noticed my circ was set at Hi speed-15GPH. I just set it back to Low speed-5 GPH. It looks like 5GPH is the correct rate for 46MBH of baseboards.
 
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Old 11-15-06, 06:21 AM
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Higher flow rates probably yield a higher return temp. However, you want 3-6 gpm through your loops, so figure out what speed gives you that.
 
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Old 11-15-06, 05:02 PM
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http://www.houseneeds.com/shop/HeatingProducts/HydronicHeating/Gauges/digitaltempgaugebuypage.asp

For those who might wanna monitor... this looks like a neat toy!
 
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Old 11-15-06, 06:40 PM
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Logamatic

For anyone following this thread: the Logamatic has a Pump logic system that shuts off the circulator when the return drops too low. That's the info that's been missing!

Pete
 
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Old 11-15-06, 07:18 PM
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Originally Posted by xiphias
I would assume that bigger is not necessarily a problem, .
Xiph be's right about this, if you oversize the expansion tank, you are wasting yer bucks though, cuz it won't "improve" anything.

I like to set the pressure on the "air" side of the bladder (remember to always set the pressure on the air side with the water side open to atmosphere!) just about one pound lower than the sytem pressure when the system is COLD.

Could go on at length about my reasons why, but that would be hijacking this thread!...

[QUOTE]I guess there is nothing I can do about the boiler cutting off below min temp. in these seasonal mild temperatures. I checked inside my boiler and signs of condensation are obvious. [QUOTE/]

Did you install a bypass valve?, you could open it a bit more in the warmer weather... the boiler would come up to temp, and inject less hot water into the system... the cycle might be shorter, but the temp would still come up... I would rather have short cycles than condensation.

If you haven't installed the bypass, why not go ahead and do that? After all, if you find out later that you don't need it, you can always just close the valve!

You could also try closing the dampers on the baseboards... less heat in the house, hotter water returning to boiler.

What are you seeing as signs of condensation ?

...or go with the logomatic that Pete suggested.

73 de Jeff
 

Last edited by NJT; 11-15-06 at 07:44 PM.
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Old 11-15-06, 07:42 PM
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Originally Posted by zaq123
oversized GPH circulator?
I just noticed my circ was set at Hi speed-15GPH. I just set it back to Low speed-5 GPH. It looks like 5GPH is the correct rate for 46MBH of baseboards.
Zaq, you do mean GPM yes ???
 
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Old 11-16-06, 04:00 AM
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Originally Posted by NJ Trooper
Zaq, you do mean GPM yes ???
LoL, yea, not per hour, GPM indeed. I just got a bit discombobulated with all these GPM, EDR, MBH etc

As far as a signs of condensation go, I can see few drip traces inside the boiler chamber.
 
 

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