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Can Old & New Hot Water Systems Be Combined?

Tremolux Member Posts: 28
We're rehabbing a beautiful, quirky, brick, 2 story, home built in 1930. There are three separate units, one downstairs, and two upstairs. They total about 3500 square feet, heated with hot water radiators. Or, more accurately, "previously heated". The utilities have been off for two years. Two first floor radiators, at the NW and SE corners, had frozen solid and fractured. Two other radiators, hanging horizontally from joists under the floors of the two N rooms ( an early form of radiant heating ) are rusted out. The boiler is over 30 years old. Not a pretty picture.

We could run hot-air up from the basement, put another furnace in the attic for the 2nd, and run returns through closets on both floors, but would rather not. We'd prefer radiator and/or radiant heat.

One post here, from several years ago, mentioned products named "HydroSolv" and "Rhomar 922" for treating old pipes. Other than that, and a pressure test, what are the chances that the 2nd floor pipes will be intact, and would remain operative if we replaced the steel pipes in the basement with Pex, and either replaced the broken radiators, or ran Pex under all the joists to heat the 1s floor? Could it work, or do they operate at completely different temperatures?


  • Hybrid System

    First floor radiant (low temperature) and upstairs radiators (high temperature) should not be a problem; it's done all the time off the same boiler.  The boiler operates at the higher temperature and a mixing valve is installed for the low temperature radiant.

    As far as your pipes, they should be in good order since the water in a hydronic system is free of oxygen and minerals.  But I'd still pressure test the pipes.

    Was this a gravity system, i.e. no pump?
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hourTwo btu/ per sq ft for degree difference for a slab
  • Tremolux
    Tremolux Member Posts: 28
    Glad to hear it!!

    Thanks for the feedback. That was good news.

    Glad we have some flexible options.

    There's an electric pump system above the boiler, and what appears to be a holding tank or expansion tank painted red hanging up between nearby joists.

    The boiler vents into a "three wide" fireplace flue, next to an ( improperly vented ) large water heater installed, but never filled or fired-up, by relatives of the ( deceased ) previous owner.

    Does this sound feasible? ...

    Start with a high-efficiency gas boiler that senses outside temp changes and adjusts accordingly, and hopefully can help provide hot water service to the house as well.

    Then pull out the first floor radiators and install Pex & aluminum frames under the joists, covered with some sort of insulation. ( note: check code to see if foam needs to be wall-boarded over ) Circulate 1st floor air with a few ceiling fans. Install ( same? ) Pex under the newly poured, enlarged, 1st floor bathroom floor.

    In the alternative, depending on comparative cost, can Pex be connected to the existing 1st floor radiators, and the broken ones replaced? Are those modern panel and/or designer radiators more efficient than cast-iron? Enough to justify the cost?

    The 1st floor gets finished with a high-efficiency gas insert in the fireplace.

    Pressure-test, clean out, and otherwise do due diligence on the 2nd floor radiator pipes and hook them into the new boiler with Pex .. which should save just a little of the heat that was being lost in that maze of cumbersome steel pipes. The pipes in the walls will have to stay put.

    Finish the West side, 2nd floor apartment with a high efficiency wood fireplace insert since there's no convenient way to get gas service to it.

    The last records the Gas Utility had showed Nov. - Feb. heating bills went from $300 to $400 and topped out over $600 a month. Ouch! Needless to say, there's a lot of insulating to do in the attic ... pretty much open to the air around the slate hip roof with just a few inches of rock-wool over the ceiling joists, but that's another story.
  • upstairs radiators (high temperature) should not be a problem

    Most definitely  a pressure test is required,, I`m curious as to why Alan thinks the top floor would be OK?

    Free of oxygen and minerals,, does water still not freeze?

    Am I missing something here?
  • Sounds

    More and more, it's sounding like you're doing a fair amount of renovation, i.e. gutting the building back down to the framing?  Yes? No?  If so, I'd replace the piping with new copper.  I'd only consider using the existing iron pipe if it's a major expense to remove wall and ceiling coverings.

    Dave: The perp. (Tremolux) says only the radiators are forsaken; I'd bet the piping is fine, but being from California, I'm at the $5 limit blackjack table.

    First floor circulator fans?  The profile for radiant heating is uniform temperatures, floor to ceiling.

    As far as mixing cast iron radiators with steel panel radiators, there's been a standing argument here that cast iron radiators will hold their heat longer than the steel radiators because there's more mass there; I'm sure it's true and if it is, some rooms may heat differently than others.

    Oh, there it is: "The pipes in the walls will have to stay put.."  OK then, replace as much as you can.

    And yes, insulate well.  But we still have know idea where you live.  Do you have any good hydronic heating contractors there?

    All the best........
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hourTwo btu/ per sq ft for degree difference for a slab
  • Tremolux
    Tremolux Member Posts: 28
    edited January 2010
    "Might be Zone 3"

    We're located in St. Louis, Missouri. For HVAC it might be "Zone 3". Whatever the terminology, it can get quite cold in Winter ... this is the coldest in 10 years ... and the Summers can get hot & very muggy. The basement is quite deep, with plenty of headroom. The original stone foundation ( circa 1890's ) was enlarged by the builder / designer / architect / resident who added steel beams to replace wood supports and poured new footings.This old brick house seems to "hold the cold" quite well. The previous owners used window units for A/C, but it's quite possible that with modern attic insulation, rebuilt vintage windows, some storms, and ceiling fans, that A/C won't be needed.There are 4 radiators on the 2nd floor West, two five footers, an 18 in. and a 20in..The East unit has 5 radiators, one 6 ft., one 3 ft., two 18 in. and a 28 in..Only two or three of them seem positioned to have straight up & down water lines in the walls. All the rest must be going off at angles that would require gutting the house to get access. There are enough holes in the interior walls already from the plumbing rehab ... ( and more to come ). The existing boiler is a Hydro-Therm model 210B ... low pressure. The face plate shows two temp. figures: 210 BTU hr. and a "capacity" of 164K BTU hr..The electric motor in back that appears to pump the water is about the size of a bench-grinder ... surprisingly small. Don't have a clue if there are any hydronic contractors out here at all. We only found out about using Pex for floor heat from an episode of "This Old House". There's been a lot of rehabbing here the past few years, much of it "gut down to the studs", but a good number of "live-in & work-on" urban pioneers as well. We called one company who specializes in radiators, and vintage ones, but never got a return call to set up a pressure test. Time to look harder.

    Is a pressure test done with compressed air or with water? A "wet" test could be problematic. Water service was turned off years ago, and won't be restored until we have both complete plumbing, and warm weather. Natural gas is similarly missing. The only utility is AC on the first floor. ( upgrades in this department are mandatory )Thanks for your support and feedback.
  • St. Louis

    Your house sounds wonderful.  I'd be camped out in your cool basement on the hot summer days.

    So, the plumbers are tearing up your house?  What about the electricians?  I've been on so many jobs where the owners have tried to save the wall coverings and by the time the subs have done their work, the owners realize that they should have gone back to the studs.  In the long run, it's cheaper and you end up with a better product.  Those old steel risers probably have minimal insulation.

    Curiously, I don't see any plumbing contractors listed for your area in "Find a Professional"  on this website.  If I were you, I'd ask around; yours can't be the only house in St. Louis with hydronic heat. St. Louis is a historic city with historic buildings that have historic heating systems like yours.  Is there a neighborhood association? 

    Failing that, search for hydronic heating suppliers in town and ask for a few references.  Call some boiler manufacturers and ask them for the numbers of a local representative or dealers; some of my favorites are:

    Viessmann Manufacturing


    Triangle Tube


    All the best,

    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hourTwo btu/ per sq ft for degree difference for a slab
  • Tremolux
    Tremolux Member Posts: 28
    Thanks for the references ... etc. etc.

    The reason we haven't considered going bare to the walls, and starting from scratch, ( besides cost ) is that about 85% of the original wood ... the floors, moldings, doors & windows, have never been painted. Unlike much of the old woodwork in town, the trim wasn't coated with stained varnish. It was intended to be seen. The floors are Oak, the doors & trim are Birch. ( It all needs refinishing, but with no paint to deal with, it's almost easy. )

    The way the house is designed, and the radiators laid-out, large sections of floor would have to be taken up on both floors, plus wall busting downstairs, just to replace the 2nd floor pipes. I'm afraid that if it fails a pressure test, we're looking at gas & ducts upstairs.

    We were unfamiliar with the term "hydronic heat" ... initially thought it referred to just floor radiant heating. Evidently it includes all water heated systems. There are lots of them here, and most are antiques. ( A local landlord told me recently that he has a guy make the rounds of his properties every Friday to drain what he called "black gunk" from all the boilers. )

    Our plumbers didn't tear up the house ... the heirs of the previous owners had it done. They had the stacks replaced, and most of the galvanized pipe removed. Almost all plastic and Pex right now. The electric situation isn't dire, but like so many other places here, there are 3 systems combined. There's some "knob & tube" in the attic, old & overloaded screw fuses in the living areas, and more or less modern circuit breakers in the basement. The alcoholic recluse who last lived in it was an electrician. Some "grounding issues" down there prompted one contractor to ask: "Who the hell did that?"

    Are there any special requirements for radiator systems that use a circulating pump as opposed to the gravity type? Does the fact that this is a pump system dictate the type of radiators and the plumbing layout?

    If there's a more efficient way of using the existing radiators & pipes, we'd certainly consider it.

    Thanks for the head start and thoughtful advice. We'll start calling those boiler companies on Monday, and see what happens.

    Attached is a photo of our previous rehab, "Chez Debris". The door, arch, & columns had 100 years of paint on them ... never again!
  • tim smith
    tim smith Member Posts: 2,544
    I might be able to help with finding someone.

    Our cousing lives in St louis/ Kirkwood. He has been rehabbing houses for some time now and he may know a local hydronics outfit. I sent you a contact email also through here. [email protected]

     Ps, beautiful house.
  • You mention

    that you have expansion tanks and a pumped system.  If it weren't for that, I'd guess that you might have a steam system.  The reason is that you mention someone draining "'black gunk' from all the boilers" which would indicate steam (not hot water)  On a steam system, the float in the low water cut-off needs to be kept clean and flushing the float chamber once a week is necessary.  Typically, you don't drain hydronic systems; it's not good for them.

    Gravity systems were popular at the turn of the century, mostly because pumps weren't around yet.  Pumps are now required to provide the flow necessary to pick up the heat on modern boilers that have a smaller heat exchange surface.

    To answer your question, radiators are sized the same for pumped vs. gravity systems.  The only thing that changes when doing a gravity conversion is that a thermostatic radiator valve (TRV) is added to the radiator piping.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hourTwo btu/ per sq ft for degree difference for a slab
  • Tremolux
    Tremolux Member Posts: 28
    "The Hypnotic Splattered Mist Is Slowly Lifting"

    We've made some progress, and learned a lot about radiator heat along the way.

    Consulted with a Radiant/Radiator specialist suggested by our favorite plumber.

    To the best of his knowledge, in this area, "beneath the joists" radiant hot-water heat can't keep an old, uninsulated, brick, home comfortable. Since the maximum temperature of the wood in these systems only reaches 85 degrees, the amount of BTU's that reach the rooms would be woefully inadequate. So much for that idea.

    On the bright side, he thinks the radiator system can be salvaged with a modern, efficient, boiler with "outside reset", and a modulating gas valve, would work fine and could be combined with an indirect domestic hot water unit.

    Here's the catch: We were told that pressure testing with compressed air could screw things up since higher pressure must be used. It could loosen parts that would be fine if tested under the lower pressure of water. However, at the present time, there is no water to the building! Catch 22. We'll have to wait until early Spring, when the risk of a hard freeze is gone, before we can have the water turned on.

    This also means that we can't have the attic foam insulated until then since if the radiator water pipes are screwed up, we'll have to Punt and have two forced air systems installed, one in the basement, going up, and another in the attic, headed down. ( Getting gas to it will be another headache, if we have to go that route. )

    Thanks to everyone who joined the conversation.

    We'll be back in touch as the project continues

    We've attached a photo of this "vintage" pile of bricks.
  • Converted Steam?

    "Horizontal radiators hanging from the rafters" sure makes me think steam--especially in north-facing rooms.  Are they perhaps rather small with no good place for a standing radiator?

    I'm fairly familiar with St. Louis architecture and heating systems both of which tend to be rather eclectic and experimental for their time. 

    Are the two pipes connecting to these hanging radiators of different size?  If so, I can almost guarantee that it was originally a steam system.
  • Tremolux
    Tremolux Member Posts: 28
    Good guess, but ... no.

    Walked over to the house this morning and took a tape measure.

    The two radiators hanging from the floor joists in the basement are 3 ft. x 2.25 ft..

    All pipes are the same size, so they probably weren't later conversions from steam.

    The North-West room is 11.5 x 12.5, with a 2 ft. x 5 ft. radiator against the West wall.

    The North-East room on the first floor is the kitchen, ( 9.5 x 13 ft. ), where an alcove beneath the East facing windows once held a 20 x 24 in. radiator that now sits beneath it in the basement. It was probably removed when the kitchen was remodeled in 1955. ( found City records that pin-pointed the date ) Either that radiator below the floor worked especially well, or it was one Cold kitchen in Winter.

    Since the kitchen floor is slated for replacement, we might look into taking it down a notch to make room for radiant heat, rather than reinstalling the old radiator. If we can do that, and do the floor of the remodeled bathroom as well, we'd have the combination system envisaged in our original posting.

    Of course, at this point, we remember the sage counsel of "The Rehab Doctor":

    "I'm sorry sir, but that wallet just has to come out."
  • Whatever yuo do,

    keep us informed and take lots of pictures.

    All the best,

    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hourTwo btu/ per sq ft for degree difference for a slab
This discussion has been closed.