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[kayakerski]

Oil boiler maintains 160 even when return is at 120

[kayakerski]

Which boiler RSI? The owb seems to maintain. Even when the return is at 120 the owb is at 170-185.

[slimjim]

That shows you that you are not moving enough water through the 3/4 inch black iron, your stove can make the heat but your piping can't deliver it.

[kayakerski]

Ah well the 1" pex definitely has to stay. Not much I can do about that unfortunately.

[kayakerski]

Do you think the 3/4 inch black iron is the issue or is it the pex too?  The only reason I'm asking is because I thought I just read somewhere that 1" pex holds a lot less water per foot than 1" black iron. It seems like 3/4" iron would hold a similar amount of water as 1" pex. Whether it flows as well is another story I guess. I'm sure the brass pex barbed couplers limit things as well.

I'm not questioning you so much as trying satisfy my own curiosity. Reqardless, its obvious that the flow is limited I guess.

[slimjim]

The reduced flow all the way around is limiting the flow but take a look at the end of a pieceof 3/4 inch black iron and a piece of 1 inch pex, I would start with either a high head circ or change out the 3/4 inch black iron.

[willieG]

i think 3/4 black iron would hold about 2.3 gallons per 100 feet and 1 inch pex would hold about 3.03 gallons per 100 feet

[slimjim]

Thank you, where did you get that info.

[RSI]

Unless you have a lot of 90s in the black iron it shouldn't be much worse than 1" pex. It is usually over 3/4" inside and 1" pex is only 7/8"

It sounds like it is just the large volume of cold water that is the problem. Is there any way you can modify the return pipes from the radiators? If you can do that, putting a zone valve in it with a small bypass around the zone valve would keep it from dumping all the cold water in so fast. A strap on aquastat could be used to open the zone valve once the returns are hot.

Another option that would probably be kind of complicated would be to get some type of a pulse controller so the pumps just run for a few seconds on and off till the cold water is all flushed into the system.

Probably the easiest is if you have an unused supply port on the boiler, run a pipe from it to the existing return port and put a tee onto it for the existing return and another pump (probably taco 007). Then put a strap on aquastat on the return pipe that turns on the new pump and have it come on whenever the return water is under 150 or 160. If you use large enough pipe you can easily get 2-3 times the GPM that is returning from the house. So if you are getting 6gpm from the house at 110° and 12 gpm from the new loop at 180° you will  have return into the boiler about 155° to 160°.

[willieG]

i just googled each type of pipe so i am reposting it

[kayakerski]

Thanks Willie. I'll have to look at the printout I have at work. I could have sworn that 1" apex was a liitle over 3 gal per 100' and 1" iron was well over 4. Maybe I miss read.

[RSI]

I forgot to mention in the last post that I just pulled the GPM numbers out of the air. If you are currently way under 6gpm you may be able to correct the low return by getting rid of some restriction but if you are currently close to the 6GPM you will need around 18-20 GPM and you will never get that.

[willieG]

you are likley right i quoted a little over three for 1 inch pex and the black iron was only for 3/4 1 inch black iron would be 4.1

[RSI]

How much 3/4" iron pipe is there in the system and is it sch 40 or 80?

[willieG]

How much 3/4" iron pipe is there in the system and is it sch 40 or 80?

you think they would use expensive schedule 80 in a house boiler application (low pressure)

but on that same note (restriction) i would almost bet if they are old cast iron rads that  the pipes (and/or) the rads have a lot of scale in them and might be reduced  a whole dang bunch?