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Replacing steam with forced hot water

> Since not high efficiency steam systems are <BR>
> available, we've been wondering about converting <BR>
> existing 2 pipe steam systems to fhw using a high <BR>
> efficiency condensing gas boiler and trying to <BR>
> utlize the existing 2 pipe radiators instead of <BR>
> installing baseboards. Does any one have <BR>
> experience with this? And, if what are the pro's <BR>
> and con's? <BR>
<BR>


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Comments

  • Charlie Wolfe
    Charlie Wolfe Member Posts: 2
    Using radiators in a FHW system

    Since not high efficiency steam systems are available, we've been wondering about converting existing 2 pipe steam systems to fhw using a high efficiency condensing gas boiler and trying to utlize the existing 2 pipe radiators instead of installing baseboards.
    Does any one have experience with this? And, if what are the pro's and con's?
  • Steamhead (in transit)
    Steamhead (in transit) Member Posts: 6,688
    This question keeps coming up

    and my answer is always the same: Don't do it!

    The two biggest problems are 1- hot water runs at over ten times the pressure of a properly functioning steam system. This increased pressure does a great job of finding weak points in the piping or radiators to leak from. I've seen places where this happened and it's not pretty. And 2- the radiators themselves might be too small to work with hot-water's reduced heat output, or might be made in such a way that hot-water won't work with them at all.

    For a more in-depth discussion of the pitfalls you may encounter, go here:

    http://www.heatinghelp.com/newsletter.cfm?Id=22

    Don't count on a condensing boiler to provide dramatically increased system efficiency. This type of boiler only runs at its peak efficiency when water temperatures are below 140 degrees. With radiators' reduced heat output on hot-water as opposed to steam, the boiler will have to run at higher than condensing temperatures much of the time. So it won't run at better efficiency than a standard boiler.

    My company does not recommend or perform this type of conversion, and will not work on a system that someone else has converted. There is just too much that can go wrong.

    I'll bet your existing 2-pipe system is actually a Vapor system. Vapor was the Cadillac of heating in its day, and is still one of the best systems out there. With a good steam boiler like Burnham's recently introduced Mega-Steam, and the system in proper repair and tune, you should be able to achieve as good a system efficiency as hot-water with the same type of boiler, and without the attendent risks of a conversion.

    Where are you located?

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  • Jamie Hall
    Jamie Hall Member Posts: 23,276
    oh no not again..

    Read Steamhead's reply. Then read it again. He really does know what he's talking about. The only thing I might add is that any minute gain in efficiency you might conceivably achieve would be so small that the pay-back on the cost of conversion would take you well past the end of the next century.

    Don't Do It!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Uni R_3
    Uni R_3 Member Posts: 299
    Pros and Cons

    Pros for steam - simplicity of design (less risk of failure / no black boxes) -- less electrical consumption (no pumps) -- no to low risk of rads leaking -- 20+ year boiler life vs ?? years -- better freeze protection in case of an extended power failure

    Pros for MC-boiler-fired FHW - I'd estimate 20-35% annual fuel savings vs a new gas-fired steam boiler -- better comfort (the rads are kept at far steadier temps) -- maintenance is reduced to an annual inspection -- simpler, more flexible and far less expensive for any piping related work -- easier to zone if needed -- much better matched with indirect DWHs

    I would think that there are situations where there are opportunities to convert (urban, larger heatload, rads that were designed for either system) and other situations that are best left with steam. The old it depends...
  • Mitch_5
    Mitch_5 Member Posts: 102
    The only way I have done it is to totally remove all the piping

    Clean and test the radiators then move the vents.

    Run new piping (pex) to each radiator and rezone accordingly. You can then use a MODCON and even take the added efficiency of a radiant style curve.

    Cast iron radiators can be run at much lower temps than copper base board or fan coils. So you can get the boiler into the sweet spot if you set it up right.

    BIG BUCKS to do it right.

    Mitch S.

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  • get the steam system balanced, make sure the near-boiler-pipng is in order, add main vents,insulate the pipes where you can, get rid of air leaks in the home, install low-e windows, put in a tekmar outdoor reset and you'll have all the comfort & efficiency.
  • Hvacman
    Hvacman Member Posts: 159
    I'm going oil to gas, steam to FHW

    What I'm doing at my house... Old WM Gold on oil has been nothing but trouble, gas line going in... Knight on order along with the PEX. I've done the calcs and the existing Sunrads will put out plenty. I'll remove/ flush/ test them and have 8 zones... future radiant zones for first floor mud room and bath as well as upstairs bath. I've grown really tired of paying for my oil mans boat. :-)
  • Dingo_3
    Dingo_3 Member Posts: 3
    There are a lot of risks I think

    not the least of which is the existing radiator size and its ability to deliver the needed heat on the coldest days. Sure the temp can be both lowered and modulated through weather responsive controls, but with the reduced output of the rads will the water temp get low enough to allow the boiler to condense often enough to recover the money spent?

    A 12 section radiator with 4 sq.ft. edr per will have a total of 48sq.ft. EDR that will release approx 11,500 btu into the room with steam. If on a typical day we only actually need 60% of that output - or 6900 btu we can do that with a FHW system - but only with 180 degree water - more efficient than steam perhaps but certainly nowhere near the condensing range - or able to justify a condensing boiler. And what is the real savings now - between a new steam boiler and a new FWH boiler - enough?

    Now, I think to get real savings and team these rads up with a condensing boiler as mentioned previously - we would need to run 130 deg water at the return and if we have a 20 deg delta-T then we might be able to release 5300 btu into the room - significantly lower than what we will need for approx 75% of the heating season. To me this is certainly not worth the loss of comfort for the winter months.

    I think my point is trying to be that there are so many things to consider here ... and even the best considerations may not lead to a properly heated room.

    Thanks to all!
  • Mitch_5
    Mitch_5 Member Posts: 102
    Dingo

    You have to admit in most cases of Old cast iron radiation it is "way" over sized for the loss.

    If you do a heat loss and compare the size of the radiation you very well may be able to get the needed btu's out.

    Boilers like the Ultra can be set up to bump up if the demand calls for to long.

    If sized, piped and programed there can be some savings and "BETTER" comfort.

    Mitch S.

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  • Steamhead (in transit)
    Steamhead (in transit) Member Posts: 6,688
    A properly functioning steam system

    will deliver the SAME comfort as hot-water. But the system must be functioning properly- that's the key. Some people swear no steam system will ever function properly, but we've proven them wrong, and have the fuel-savings numbers to back it up.

    And if you "bump up" the Ultra or any condensing boiler, it goes out of condensing range- bye-bye, 90%+ efficiency. What you end up with is a very expensive and complicated standard-efficiency boiler.

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  • Steamhead (in transit)
    Steamhead (in transit) Member Posts: 6,688
    So you will now be paying

    for the gas utility CEO's Rolls-Royce.

    We have several oil-fired W-M Golds out there that run fine. If yours isn't, I bet the oil company wasn't setting it up right.

    Hope your Sunrads don't leak. Remember if you go to HW you're increasing the pressure over ten times. This WILL do a great job of finding weak points.....

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  • Uni R_3
    Uni R_3 Member Posts: 299
    Maybe this would help show the potential savings...

    Let's assume the following efficiency points for return temperatures on a condensing boiler.

    Up to 99°F 96%

    100 - 109° 95%

    110 - 119° 94%

    120 - 129° 91%

    130 - 139° 88%

    140 - 149° 85%

    150° and up 84%


    Furthermore, let's assume that at -4°F, the rads will require the full 212° supply and at 72° only 72°. This makes for a steep slope of 1.84. I doubt any house would ever need the full 212° on a continuous basis at design but this is to show an extreme example. We'll say that the ΔT is only 10°, so we'll take 10° off to get the return temps. Most modcons can't exceed a 200° supply but let's skip that fact for now.

    If we plot average daily temps for Toronto Island airport (since I have them) from mid-December to May 5th of this past winter, and exclude the fall shoulder season which would only increase the overall average, I still get an average efficiency of 87.2%. I'm not sure of any conventional gas boiler that can get a seasonal efficiency anywhere near this level.

    The attached graph uses these numbers.

    ----- ----- ----- ----- -----

    Drop the maximum supply temperature to a more realistic 180° and the average climbs to over 90%. (1.42 slope)

    At 160° max supply, that average works out to more than 92% while still not including the milder fall shoulder season. (1.16 slope)

    If you think the efficiency numbers should be even lower, consider that with a 180° supply requirement and efficiencies of only 90% up to 119°, 85% to 139°, and 80% above that still averages out to over 87%. No conventional gas boiler can do that and I doubt any oil boiler would ever have the same seasonal efficiency as its AFUE number, especially in the shoulder seasons.

    This is why I say that the annual savings would be 20% to 35% higher with a condensing boiler.
  • Uni R_3
    Uni R_3 Member Posts: 299
    Outdoor reset on steam?

    How does that work?
  • Tony Conner_2
    Tony Conner_2 Member Posts: 443
    Unless...

    ... the steam system has been absolutely butchered, you'll probably be 15 years getting a payback on converting to a hot water system. For maybe 10% of the project cost of converting to hot water, I'd bet that the steam system can be made to come pretty close, efficiency wise.
  • Perry_3
    Perry_3 Member Posts: 498
    I see two options here...

    Option 1: The system is in reasonable shape and can be fixed up and have a new boiler installed; AND you are not planning on tearing out the walls for a general house refurb.

    Stick to what Steamhead is telling you. You have nothing to gain and perhaps a lot to loose by convering to a hot water circuit.

    Option 2: The piping is known to have lots of condition issues (and I'm not talking of just a section or two that can be replaced). This is probably rare - but it can exist. Also - or you are planning this anyway; you are OK with doing a general refurbishment of the house that includes gutting the walls, modern insulation, window replacements, wiring, etc.

    In this case the existing steam radiators and heating system are going to be almost certainly going to be way oversized.... once you substaintially tighten up the envelope. Proper heat loss calcs and proper sizing of a good mod/con system will pay off. Of course, you would replace all the piping to and from the radiators.

    Properely funtioning steam systems are great, and they rarely need to be replaced due to condition (as long as the vents and boiler are properely maintained). But if you are going to replace them - you had better at least do it right - and doing it right is not cheap.

    Perry


  • the same way it does for any other reset. It takes temps from 2 or more different locations & figures the run time of the boiler. Check it out @ Tekmars web site. It's pretty cool.
  • Rick_65
    Rick_65 Member Posts: 4


    I've done alot of steam to water conversions with great success in the past 15yrs. What we've typically found is that in the past, they used to oversize the radiators, making sure they have enough capacity to heat the room. Once we do a heat loss calculation, especially if they've done any building improvements, we find out that you don't need that much radiator, or that you can run the radiation at much lower water temps and still heat the room. It takes alittle up front work but we've seen 30 to 50 percent savings when we convert these systems and a much better comfort level. My experience is that any piping above the water line of the steam boiler will hold water. We never utilize wet returns, and with dry returns, you have to sometimes increase the size based on the flow rates required. In larger systems, we are using a condensing boiler and running it as long as we can to stay in condensing mode, and a cast boiler to help bump up the water temps when required.
  • Steamhead (in transit)
    Steamhead (in transit) Member Posts: 6,688
    Then

    you haven't seen the disasters I've seen, where the piping and radiators above the waterline turned to Swiss cheese when converted.

    That's one of the main reasons we don't touch these conversions. Who wants to be "the last one who worked on it"?

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  • Steamhead (in transit)
    Steamhead (in transit) Member Posts: 6,688
    Maybe not with an atmospheric boiler

    you'd need a power gas burner to do that. I'll bet in five years, you won't be able to buy atmospheric boilers any more, due to their low efficiency. That might make landlords start an open revolt.....

    Some of the more recent power gas burner applications are promising- check out the Dynatherm with the Carlin EZ-Gas here:

    http://www.dynathermboiler.com/html/gas_fired_boilers.html

    and my favorite, the Solaia which uses the HeatWise gas burner. We have one of these running in my neighborhood:

    http://www.boyertownfurnace.com/pages/products-solaia-boilers.htm

    Don't forget, the Burnham Mega-Steam has an 86% AFUE on oil, and if Burnham offers it with a gas burner it'll be the most efficient gas-fired steamer out there. Note to Burnham: HINT!!!

    All of the above boilers can be switched to the other fuel by installing the appropriate burner. And they don't have the complication factor of condensing boilers.


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  • Uni R_3
    Uni R_3 Member Posts: 299
    Any other reset?

    I just looked again and noticed the 269 is for steam. Every other ODR I've ever seen regulates the water supply temps so you can see where my question comes from.
  • Steamhead (in transit)
    Steamhead (in transit) Member Posts: 6,688
    The 269

    varies the quantity of steam produced per cycle, based on outdoor temperature. If the system is set up correctly, all the radiators will be heated to about the same percentage when the boiler shuts off. Occupants can limit the amount of heat their rads produce by using TRVs.

    We have several 269 units out there and they work great once set up.

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This discussion has been closed.