# Series Loop on cast iron radiators?



## jim connolly

Looking at a small reno heating job, homeowner wants to use cast-iron radiators left over from previous heating system. I'm to run the new lines and connect to rads, install boiler etc. 
I want to keep the piping design simple. Thinking about a series loop for each zone. Four zones, each has 4-7 rads. Haven't calculated GPM or head yet. Just looking for some feedback. I've only ever used the series loop design for baseboard jobs. Will it work for CI radiators, or will the rads offer too much resistance?
Whaddaya think?


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## ZL700

jim connolly said:


> Looking at a small reno heating job, homeowner wants to use cast-iron radiators left over from previous heating system. I'm to run the new lines and connect to rads, install boiler etc.
> I want to keep the piping design simple. Thinking about a series loop for each zone. Four zones, each has 4-7 rads. Haven't calculated GPM or head yet. Just looking for some feedback. I've only ever used the series loop design for baseboard jobs. Will it work for CI radiators, or will the rads offer too much resistance?
> Whaddaya think?


Series loops on cast iron radiators is bad, the rads at the end will likely be too cold and other concerns are shocking boiler and condensing if its not supposed to

Best piping install in order would be
1. 2-pipe, reverse return
2. 2-pipe, direct return
3. monoflo
4. home run from manifold


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## jim connolly

ZL700 said:


> Series loops on cast iron radiators is bad, the rads at the end will likely be too cold and other concerns are shocking boiler and condensing if its not supposed to
> 
> Best piping install in order would be
> 1. 2-pipe, reverse return
> 2. 2-pipe, direct return
> 3. monoflo
> 4. home run from manifold


 
Thanks ZL, good advice. I'm running an electric boiler (No NG around here) so condensing is not an issue but boiler shock is.
I was thinking about reverse-return but wanted to keep the runs simple. I do, however, have room to put a reverse-return system together as the house is completely gutted. This looks like my best option. A bit more pipe, but no headaches with balancing.
From what I hear, direct return can be a pain and balancing valves are nedded to avoid the last rad in line getting bypassed.
Monoflo could work as well.


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## ZL700

jim connolly said:


> Thanks ZL, good advice. I'm running an electric boiler (No NG around here) so condensing is not an issue but boiler shock is.
> I was thinking about reverse-return but wanted to keep the runs simple. I do, however, have room to put a reverse-return system together as the house is completely gutted. This looks like my best option. A bit more pipe, but no headaches with balancing.
> From what I hear, direct return can be a pain and balancing valves are nedded to avoid the last rad in line getting bypassed.
> Monoflo could work as well.


Nice thing about reverse return is you can use thermostatic radiator valves or they can close down manual rad valves and it just redistributes flow amongst other rads on that loop


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## mtfallsmikey

Or...primary-secondary piping


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## ZL700

Yea, that how you do it single pipe and a circulator on every radiator :laughing:


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## nhmaster3015

We do a lot of these conversions. I like to install manifolds at the boiler and run individual feed and return lines using 5/8 heat pex to each radiator. A single circulator on the supply feeds everything. Each zone has a shutoff at the manifold or for precise control, zone valves can be installed either at the manifold or on the radiators. No primary secondary piping required although on a low mass boiler a 3 way mixing valve or a manual mixing valve is a good idea. Look into hydronic separators also. I hate primary secondary. Huge waste of money and time.


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## Gettinit

nhmaster3015 said:


> We do a lot of these conversions. I like to install manifolds at the boiler and run individual feed and return lines using 5/8 heat pex to each radiator. A single circulator on the supply feeds everything. Each zone has a shutoff at the manifold or for precise control, zone valves can be installed either at the manifold or on the radiators. No primary secondary piping required although on a low mass boiler a 3 way mixing valve or a manual mixing valve is a good idea. Look into hydronic separators also. I hate primary secondary. Huge waste of money and time.


Or possibly a thermostatic mixing valve to ensure higher temps back to the boiler.


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## jim connolly

nhmaster3015 said:


> We do a lot of these conversions. I like to install manifolds at the boiler and run individual feed and return lines using 5/8 heat pex to each radiator. A single circulator on the supply feeds everything. Each zone has a shutoff at the manifold or for precise control, zone valves can be installed either at the manifold or on the radiators. No primary secondary piping required although on a low mass boiler a 3 way mixing valve or a manual mixing valve is a good idea. Look into hydronic separators also. I hate primary secondary. Huge waste of money and time.


I'm interested in this idea too. A couple years back John Siegenthaler wrote an article about getting back to simpler system designs, in one system he had home-run circuits off the boiler in 5/8" heating Pex and a TRV on each rad. All the rads were the wall-hung steel panel type. Looked like a pretty simple install.


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## Catlin987987

nhmaster3015 said:


> I hate primary secondary. Huge waste of money and time.


How do you figure that?


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## nhmaster3015

jim connolly said:


> I'm interested in this idea too. A couple years back John Siegenthaler wrote an article about getting back to simpler system designs, in one system he had home-run circuits off the boiler in 5/8" heating Pex and a TRV on each rad. All the rads were the wall-hung steel panel type. Looked like a pretty simple install.


My own house is piped that way using cast iron radiators. Works super


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## nhmaster3015

Catlin987987 said:


> How do you figure that?


Time and materials. A hydronic separator costs less and takes less time to install


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## Catlin987987

nhmaster3015 said:


> Time and materials. A hydronic separator costs less and takes less time to install


How does a $500+ hydronic separator cost more then two Tees


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