Reusing steam radiators for condensing boiler

dbk

Hi heating experts! I'm doing (and by doing I mean writing checks, I'm no contractor) a gut renovation of a townhouse in Brooklyn. I have a bunch of cast iron radiators which were previously in use in a steam system. Not sure how long it was in there, probably at least 20 years. I rather like them, and was planning to reuse them in a new hydronic system, with a high efficiency Navien condensing boiler and all new pipe work. On inspection the radiators showed signs of interior rust, extent unknown. I'm being encouraged to replace them, although I'm far from confident that the advice is actually coming from an HVAC expert (many cooks in the kitchen - plumber, contractor, architect etc). Is getting them flushed out and installing a dirt separator or filter a viable option at least sometimes, or should I not even be considering it? Another thing that worries me is that if I go with new cast iron radiators, won't they eventually rust too?

Thanks!

Snowmelt

Your good, just make sure you can bleed them from the top, the two or three things, get the hydro dirt air and magnet from calleffi, use the sentinel cleaner and inhibitor. If you use the manifold from watts still get the dirt mag with an air seperator. Also get the outdoor reset, most people don't get it just because they don't know.

BobC

At a minimum I would have them tested after cleaning to make sure they are leak free and will handle the increased pressure. Test them with air, not water.

Bob

Gordy

I,don't know the extent of the renovation, but if your calculating EDR of the radiators those steam radiators would be smaller than a hot water radiator. Steam uses higher temps than a water based system therefore the rads could be smaller.

But if your Reno is upgrading the envelope insulation, and air sealing you may be fine.

To answer your original question flush them out, pressure test, and if they pass use them.

dbk

Thanks all! And yes, the envelope is seeing a thorough overhaul. Previously it had no insulation at all and single pane wooden windows, so there was plenty of room for improvement!

nicholas bonham-carter

To reiterate, make sure these radiators are connected at the top and bottom, so they can be used with water.
Early steam only rads were connected only at the bottom, and can not be used for water, as they cannot be bled of air.--NBC

j a_2

First off its sad to see another steam system bite the dust….That said at least your using c/i rads as a condensing boiler loves the higher mass water, it saves you from installing a buffer tank…For the guy that normally does it its fairly simple to convert the rads, I believe in doing a hydro static check, you may have better luck drilling and tapping a new bleeder port,than getting the old one out,if there is one there…You will have to rebush the lower tappings and install either straight or angel valves….And plug the old steam vent port….Do not spend the big bucks on the make over only to have it ruined by 100 year old leaking rads.not done correctly...

gennady

There is no problem with re-using CI radiators in hot water system. Installing dirtmags, hydro separator, cleaning, flashing and water treatments with sentinel will keep system clean. I do not recommend to convert from steam to hot water system. Properly done steam system is on par with hydronic one, allows to set temperature in each room individually and as economical, efficient and comfortable. Judging from choice of the boiler and the fact that you mention plumber as a heating contractor, you are setting yourself up for inferior system compared to what you have now.

j a_2

Gennady, please tell me your not saying a plumber is not a good heating contractor…

Gordy

I just want to say there are better" boiler" choices out there.

dbk

Thanks again for all the advice. Re keeping the steam, not a sensible option I dont think, as the layout was changing completely and we wanted radiant in the basement. It would have been a brand new install whatever we did, and in any case the old boiler was just physically too large. Re the installer, he is a qualified HVAC guy, he just works for the GC rather than me directly and I'm getting the game of telephone. Seems like I need to get more involved. Will check the ports on the radiators and get them tested, along with the other precautions described. They're not truly ancient items, I think the system was replaced some time. The old boiler was maybe 20 yes old, and yes, it worked well. Gordy, you're saying Navien isn't a good brand, am I understanding you right?

Gordy

I think Navien is getting better so long as the installer understands it's heating side limitations.

A lot depends how far your taking your new hot water system for control. ODR with trvs, and delta p pumping is a nice strategy.

Fire tube heat exchangers are far better. Your btu requirements for the heat loss which I hope is your contractors first step will start to tell the story. This is where the design begins. You need a room by room heatloss calc first.

vaporvac

I think I'm seeing the limitations of your advisors in that switch from steam to HW, especially if this is two-pipe steam which it has to be in order to re-use the rads. One can easily take a Hot Water loop off the steam boiler and use that for your radiant. It's done all the time. Keep the steam anc ADD hot water. Save yourself the comfort, worry of freezing pipes and expense. Get a steam person to review this and thank us all later.
If it's a large system, twin the boiler and reap the rewards. Seriously, I almost did it myself and thank DHolohan for this site whenever I look at my new system and get my gas bill.

j a_2

But why the plumber statement. As I have seen this before on this site...not liking it

Gordy

It is an umbrella statement. Any trade has its branches of refined expertise. There is no reason it cant be more than one.

j a_2

Sorry that u think that way about plumbers

Gordy

Seriously, I did not think i was being negative about plumbers??

NYC007

dbk, I am in Queens and I am no Heating expert at all, however I would definitely get yourself involved 100% - I have done what you plan, it has worked great for the past 10 years and those old radiators cook and stay HOT! - Today it seems contractors just don't care as they did from years ago~ btw *Digging vaporvacs advise

Jamie Hall

At some risk of adding fuel to a fire... I have two superb craftsmen who help me with the place I care for. One of them is an excellent steam man,one of the best -- and a pretty good plumber, to boot, and I dare say gets a good chunk of his income from plumbing. The other is a first class plumber -- and would be the first to tell you that though he can do steam, he'd much rather not thank you very much. Does that make him less of a plumber? No. Does it make him less of a craftsman? No.

Bottom line -- I split the work. And respect both of these men tremendously!

KC_Jones

Not speaking specifically about any trade, but to me it's about a person's natural ability and their willingness to learn. It's not about a title. I have seen people who are beautiful cabinet makers, but never did it professionally. I have seen people who could do plumbing work with their eyes closed, but didn't do it for a living. On the other side I am sure we have all seen people with the title that do terrible work. It's more about the person than a title...that's just my opinion.

j a_2

There is nothing better than a good mechanic….with natural ability….My point about the negative plumbing comment was that here in the Commonwealth of Mass. It requires a lic. plumber or gas fitter to install a gas boiler…its the law……So anyone that advertises has to have a lic…Clearly not all plumbers are heating guys,and thats fine…Lots of people refer to this site for advise, and The find a contractor section….So all that said I wish non plumbers would keep the comments more specific….

RobG

I've had doctors that were so awful that I would have rather have had a good plumber operate on me! At least the good plumber would RTFM before he did the surgery!

Gordy

I learned through my wife, and daughters car accident. It's amazing all the specialization in the medical field. Just in orthopedic. Broken hand see this guy. Foot see that guy. Leg a different one. What a fiasco. Never even knew.

To JA sorry if I offend you not my intent. All I meant was any trade has its specialized areas. But that's not to say a talented individual can't have more than one area of specialty. It takes ambition, and dedication. No reason a plumber can't be a hydronisist, or a steamer. Johnny NY wrote it very well in a post for a thread. His brother likes the plumbing he likes the heating. Does not mean each can not do the other well.

j a_2

Most important, best of luck to your wife and daughter…They are so precious…to all of us….Yea, I do get a bit uptight when people on this site hit on plumbers…I, as I am sure others do, take great pride in my work…I have come to this site may times over the years, sometimes to share, and sometimes to ask,and sometimes just to have fun…At 62+ I still listen and learn…Not that I haven’t been accused of being stubborn…Oh well….

dbk

Thanks again everyone. I'm trying to work out if the Navien NHB boilers need a separate part for outdoor temperature sensing or whether they somehow have it 'built in', as their literature seems to suggest. I guess it'd be measuring the temperature of the air coming through the input pipe? That doesn't sound completely crazy, although my pipe run is almost 30' through heated areas. The NCB (combination) boilers list a separate outdoor sensor part as an accessory, but the NHB don't seem to.

Not going to weigh in on the plumber issue, other than to say that my new drainage system is a work of art...

Thanks!