Steam boiler with hydronic loop?

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Old 01-09-07, 09:45 AM
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Question Steam boiler with hydronic loop?

Basement is poorly heated with 220 electric baseboard. I want to do away with it. The steam boiler is in the basement. I've heard a Hydronic loop can be integrated with a steam boiler. Is it possible and how? I'm not steam savy.
I do understand a good deal of hydronic heating. I've succesfully installed a 4 zone (Munchkin) hydronic system complete with indirect water heater and runtal radiators (I researched the fun out of it).
Thanks in advance.
 
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Old 01-09-07, 10:18 AM
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Find a couple of tappings below the water line and use a bronze circ is the advice that I've seen. Is your basement insulated? If not, that's what I'd do first.
 
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Old 01-09-07, 10:42 AM
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I've read that most use a "wet" return (water from return pipe enters below the water level) - 01. what about "dirty water" or "sludge" in steam return lines? is that a concern for a circ pump? 02. if I tap into it below the water line can I pump up away or must my new run of hydronic heat remain below the water line? could this be done with a check/backflow inline? 03. do i also need a mixing valve because steam is over 212+ and typically a baseboard would run at -180?
 
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Old 01-09-07, 12:05 PM
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I would strongly suggest that you stay away from the existing return line of your steam system. You may be able to utilize the drain fitting on the boiler for a hot water return by installing a tee between the boiler and the drain valve.

You could use a tempering valve but it is one more thing to go wrong. I would probably design the baseboards for operation at the boiler temperature. I strongly suggest that rather than using tin/lead soft solder in doing the piping that you at least use lead free solder as it has a higher melting point than tin/lead solder. Even better would be to silver solder or brazing.

You absolutely want to install the circulator pump discharging FROM the boiler. Because the temperature of the water is only slightly below the boiling point at whatever pressure is maintained within the boiler the possibility of vapor lock would be high if the circulator was on the return side of the baseboard loop.

For the same reason (vapor/water pressure/temperature relationship) it would be best to keep all of the hot water heating piping below the waterline maintained in the boiler. You shouldn't need an air scoop, air vents or expansion tank. A flow check is a good idea but perhaps not necessary.

Another way would be to use a secondary system where the boiler water first released heat through a closed heat exchanger to a tank that would supply the hot water heating system. In this case the secondary tank would be considered as a hot water heating boiler and all the rest of the system would follow the protocols of a standard hot water heating system including the air vents and expansion tanks.
 

Last edited by Furd; 01-09-07 at 01:02 PM.
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Old 01-09-07, 12:43 PM
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thanks. this is starting to make sense. "you may be able to utilize the drain fitting on the boiler for a hot water return by installing a tee between the boiler and the drain valve". QUESTION 01.- where does the "circulator pump discharging FROM the boiler" get the water from?
QUESTION 02. involves "I would probably design the baseboards for operation at the boiler temperature". isn't the water too hot? I will probably use burnham cast iron baseboard.
 
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Old 01-09-07, 01:01 PM
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"QUESTION 01.- where does the "circulator pump discharging FROM the boiler" get the water from?"

You will need to find a tapping that is below the waterline to connect the circulator pump. Do not connect to any of the water column (water sight gauge or low water feeder/cutout) connections that are currently in use. Some boilers have connection tappings on either side for the water column and you may have some spare tappings. If you do not have any spare tappings you may be out of luck.


"QUESTION 02. involves "I would probably design the baseboards for operation at the boiler temperature". isn't the water too hot? I will probably use burnham cast iron baseboard."

No. If you are able to make all piping and connections with steel pipe then that is preferable to using copper and soldered fittings in this particular instance. Most finned tube baseboards are rated with a "design" temperature of 180 degree F. water. Using hotter water means that the baseboard will put out a greater number of BTU's per foot of length wich would allow using a shorter run of baseboard. Even running 215 degree water the baseboard convector will be cooler than most electric baseboard heaters. You certainly could install a three-way temperature control valve but unless you have a rather extensive baseboard configuration it won't work all that well. I vote for simple. Maybe a few details on your proposed installation would help me to better answer your questions.
 
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Old 01-09-07, 01:37 PM
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ok. now i've got it. use a tapping in the boler (below water line). pump away. return through another taping on the opposite side of the boiler (again, below water line) or use the boiler drain tap with a tee in between. was looking over my munchkin hydronic install (a few years old) and figured i should use a by-pass line (with a valve to control the flow). this way some of the return water which expelled heat goes around the outside of the boiler and will be mixed with the hotter supply and i can control the temp. (i'll place a temp gauge in-line and tweek the by-pass line valve). the reason i wanted to go "up" even though this is basement install is becasue of doorway thresholds. if i go "up" no airvents, right? otherwise i'm risking air entry somewhere. with this configuration can i use copper? the total run of pipe is about 80' with 20'+ of baseboard.
 
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Old 01-09-07, 03:10 PM
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Your supply and return tappings do not need to be on different sides of the boiler, just tappings that are not presently being used for the steam heat return, water gauge, water feeder or low water cutout.

I strongly suggest that you do not run any of the piping for this new system above the normal water level in the boiler. The only thing that will keep this water from flashing to steam is the head pressure of the water above it with a tiny bit of help from the circulator when it is running. Since the tiny bit of pressure exerted by the circulator is difficult to calculate (and also because it "disappears" when the circulator stops) any water that is in piping above the water level in the boiler is likely to turn to steam and that will "bind up" the water flow just as surely as air in a more conventional forced hot water system.

It is the pressure/temperature relationship between steam and water that makes this a challenging project. If you could absolutely ensure that the supply water temperature was always below the boiling point corresponding to the lowest internal pressure of the entire system (including the water in the boiler) then you could have the piping go higher than the boiler water level. Unfortunately this is pretty difficult to accomplish without some kind of heatsink immediately after the pump and prior to reaching the higher piping. The control for this also introduces complications.

I would strongly suggest that you run the piping as low as possible. At doorways you could either chip out a trench in the concrete (assuming a concrete floor in your basement) and run the pipe in the trench, then covering the trench either with a steel plate or you could just run the pipe on the floor and build a wooden threshhold with tapered sides to allow for passage through the doorway.

Yes, you may use copper tubing/pipe for this system. I suggested all steel piping because you mentioned cast iron baseboard convector units. Most (if not all) CI baseboards will have threaded connections and if you were to use copper piping you will need threaded adapters to connect to the baseboards. Connecting copper and cast iron (or steel) directly will cause corrosion. You really need to install a brass intermediary piece between copper and either CI or steel. Making the piping all steel from the beginning may be a bit more difficult with having to cut and thread the pipe but it will be a better installation and be less prone to leaks down the road.

You also need to consider the control of this new system. If you plan on using this when your boiler is steaming, i.e. when the rest of the house is on a normal heating cycle, you can probably get away without having to modify the boiler controls. Understand that if the main section of the house goes for a long period of time without a "call for heat" the boiler may cool down considerably if the basement is requiring heat. If you will be in a situation where the basement will often be using heat when the steam portion is not then you will need some additional controls to keep the boiler temperature up.

Then there is the matter of controlling the heat in the basement. The simplest method, applicable if you are heating just one room, would be to install a line-voltage thermostat to directly control the circulator. You may be able to use a thermostat from your existing electric baseboards.
 
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Old 01-09-07, 04:03 PM
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Furd brings up a good point about the difference in heating demand between the basement and the upper floor(s) where the thermostat is.
My house has this problem.
The electric forced air furnace has to be suplemented with electric baseboards to keep the basement a constant temperature.

In outdoor temperatures where you would need heat in the basement how much run time does your boiler see per day.
 
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Old 01-09-07, 04:38 PM
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"The only thing that will keep this water from flashing to steam is the head pressure of the water above it" . Question1 - in the proposed new loop the water would never be as hot as the boiler water, or would it? so how would it flash to steam? With a short bypass around the boiler it would instantly mix water from the end of the loop (a considerably lower temp water) before entering the circ pump.
 
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Old 01-09-07, 05:19 PM
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I don't know what you mean by "a short bypass around the boiler". Are you planning on a primary / secondary system with a mixing valve in the secondary loop going to the new baseboard convectors? Quite honestly I do not see any other way to positively eliminate the possibility of getting boiler temperature water into the new hot water heating loop. I'll say this, if you decide to run the piping above the water level of the boiler you greatly expand the chances of "steam binding" that piping system. If it happens I guarantee that you will not be happy.

I've given you my advice, what you choose to do is up to you.
 
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Old 01-09-07, 05:39 PM
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belive me - i appreciate everyones advice!. i was imagining (for simple illustration purposes) a circular loop with a steam boiler at the bottom. So maybe boiler, valve, circ pump, flow control---- radiator-----flow control, boiler.
now just before the return to boiler i put a T that allows a portion of the return water to also "by-pass" the boiler and re-connect to the supply before the circ pump. i would put a valve on this to regulate the water flow. also i would put a temp gauge on the supply.
does this make sense? again, thank you for your educated opinion.
 
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Old 01-09-07, 05:53 PM
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furd - when stephen says bypass i think he means a manual mixing valve, so he can mix down the boiler temps by recirculating the water coming back from the baseboard

stephen - when you say bypass furd is wondering why you'd bypass your heating system


BS========(>>>)===bbS
........||
........\\ <valve
........||
BR===============bbR

ignore the dots...
 
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Old 01-09-07, 06:13 PM
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If I am properly envisioning and sketching what you propose I think you are asking for trouble. You simply cannot adjust manual valves to cover your a** under all eventualities. A thermostatically operated three-way valve on the pump suction MAY work but I would prefer to see a thermostatic FOUR-way valve on the pump discharge. Either way introduces possible control problems. The more valves and controls you install the more costly the system and the more areas for it to go wrong. I tend to prefer simplicity over complexity, especially in residential situations. Not that it can't be done, control of energy systems is what I specialized in when still gainfully employed, it is just that specialized control systems tend to cost lots of dollars and rarely function without periodic inspection and maintenance.

Of course if this were a properly pressurized hot water boiler instead of a steam boiler your proposal would make good sense. Trouble is, a residential steam heating system is a vastly different animal from a hot water system. Combining the two, while possible, is not an easy task.

Now obviously I am not you, but if I were, the slight inconvenience of installing the piping under the door opening would far outweigh the added and quite likely continuing complications of running the piping system overhead.

Best of luck with your project.
 
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Old 01-09-07, 06:48 PM
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i was attempting to state what "Who" stated. "a manual mixing valve, so (I) can mix down the boiler temps by recirculating the water coming back from the baseboard". i thought that would in effect prevent the hydronic loop from ever reaching flash point.

all of your points are well taken. if I dig a trough at the door thresholds what do i line it with? (to protect the steel/coper from the cement slab)
 
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Old 01-09-07, 09:21 PM
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Smile Personal experience

I've installed a hydronic loop off a steam boiler before & made a few mistakes before getting it right. I first had the supply go from a tapping on the bottom of the boiler, and the return go to a tapping on the bottom of the boiler on the other side. I found that the boiler I was working on was much cooler at the bottom than the top. The result was that I was circulating luke-warm water. I then put the return just below the water line with a check valve at the boiler, and it worked great because the cold water was brought to the top of the boiler, making the temp more even in the boiler. Steam didn't go into the bottom tapping, so it didn't get air bound. I didn't put in a mud trap/sediment filter, but probbably should have. I used an iron circulator. Hey Who, why do you reccomend a bronze one? I would definitely insulate first!
 
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Old 01-09-07, 09:25 PM
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Question low limit

Almost forgot, does your boiler have a low limit control?
 
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Old 01-09-07, 09:48 PM
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interesting. cooler at the bottom than at the top. that makes good sense. it was probably wise not to "put in a mud trap/sediment filter" because it would clog resulting in a pressure drop (although i don't know how muddy these things get). a good circulator with a big impeller (i work with pools in the summer months) should not be effected by sediment.
maybe bronze because iron can rust?? although this is a closed loop so that shouldn't be too big an issue.
as for the low-limit control i'll have to get back to you.
 
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Old 01-09-07, 09:55 PM
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I would use a bronze circ because it is an open system. If an iron circ could survive 5 years in there then maybe iron but bronze would just seem right - at triple the price though...
 
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Old 01-09-07, 10:00 PM
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Gentlemen, stop the presses. 5 heads are almost as good as one! In about 2-3 days I think we would have had this all sorted out. You HAVE got to read this post!!!
http://www.heatinghelp.com/heating_howcome6.cfm
Pat yourselves on the back. Some of your suggections were spot on. I have to get back to reading his.
 
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Old 01-10-07, 03:00 PM
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Well, there you are. I was basing my response on physics and thermodynamics, not on any personal experience. I personally would still be highly concerned about "steam binding" in the elevated sections of piping but the people at Heating Help have the real world experience that I do not have in this particular situation.

As for the issue of cast iron vs. bronze for the circulator pump...the water in a steam boiler is not a "closed loop", far from it. The water in a steam heating system "breathes" every time the system cycles. A small amount of water is always lost through the radiator air vents when the heat cycle begins and a small amount of air in "drawn in" through the air vents when the radiator cools. Because of the water loss through the air vents the steam boiler (as opposed to a hot water boiler) "takes on" water quite often during its normal course of operation. The water in a steam boiler is going to be more corrosive than the water (assuming no leaks) in a hot water boiler. Still, I think a CI pump would give reasonable service and it removes the problem of dissimilar metals in the system.

Sediment in the boiler. Because of the normal operation of losing water through the air vents and taking on additional water via the automatic water feeder, a steam boiler will concentrate any impurities that are present in the make-up water. It is imperative that these impurities not be allowed to bulid up, especially in the water feeder and low water cut out devices. You need to periodically "blow down" the lwc/o, auto feeder and the boiler proper. Do this when the burner is not running, preferably when the boiler has not fired for a time. It is not necessary to blow out a large quantity of water at any one time but short "blows" on a regular basis are necessary. Depending on how much water is lost in normal operation and the quality of the incoming water you may need to blow down as often as once a week or as infrequently as once a month.
 
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Old 01-11-07, 06:01 AM
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on the subject of water impurities, would it make sense to install a filter on the cold water input? as far as the loop is concerned - I'll think i'll keep it low like you suggested. the theory is there for the overhead but after re-reading, the risks don't seem to outweigh the little added work in a trough at the thresholds.
what should i be lining the threshold with?
 
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Old 01-11-07, 07:31 AM
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i would give thought to putting a wye strainer in place between where you'll be tapping in for your supply from the boiler and the circ

no idea on a water filter - is this just for any makeup water?
 
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Old 01-11-07, 07:45 AM
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i had to look up wye strainer http://www.backflowparts.com/catalog/showProduct.cfm?vendorID=16&pageNumber=3
i get that much but i was thinking about filtering the make-up water. where is the crud/sediment coming from? we have a lot of rust/iron particles in the water here where i live - is that the source of it? hence the filter.
 
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Old 01-11-07, 12:02 PM
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If you install the wye strainer be sure to install valves on either side so that you can isolate the strainer and remove the screen for cleaning. Don't rely on a "blow out" valve to properly clean the screen.

As for "lining the trench"...You're asking an important question with many answers depending on the condition of the soil in that trench. You want to keep the piping dry and you want to insulate it to reduce heat loss into the soil. Because it is possible that the pipe temperature could reach a temperature as high as the boiler water, in excess of 212 degrees, I would suggest that you not use the flexible foam pipe insulation that is readily available for domestic water lines. It may be just fine, I have used that material on lines running at 180 degrees without failure but it was probably pushing the envelope.

If your soil is dry then I would recommend using fiberglass insulation. If you can get some rigid, preformed fiberglass of the correct size that would be ideal. Simply wrapping the pipe with soft fiberglass would be okay, allow enough fiberglass that the pipe is free to expand and contract after backfilling the trench.

Also be sure to allow for expansion / contraction where the piping exits form the concrete slab. Ideally you should "sleeve" these exit points with a pipe at least double the diameter of the heating pipe. The sleeve can be plastic pipe and the space around the heating pipe filled loosely with fiberglass.
 
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Old 01-11-07, 01:20 PM
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Thanks for the valve/wye tip. Soil is wet. I like your ideas - I think i'm going to cut a wide/long enough trough in the slab, dig it out, fill it with cement and set a length of scrap 6" diameter pvc (cut lengthwise) embedded into the wet cement. then i'll put (as per your suggestion) preformed fiberglass insulation on the pipe and get a buddy to cut me a sturdy steel threshold.
Thanks everybody for all the advice and wisdom. If you have anymore suggestions feel free.
 
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Old 01-11-07, 06:52 PM
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Yep, with wet soil the concrete utility trench is the way to go. If you make the utility trench wide and deep enough to allow for some air space around the pipe and then use a steel cover you don't even need to insulate the pipe. The heat loss will just serve to heat the room. You will want to insulate the exposed piping for safety against accidental burns if you were to touch the pipe. Or, if you don't mind a funky look you could install expanded metal over the pipe in a way as to prevent contact with the pipe. This method would allow the heat lost in the piping to heat the room via radiation.
 
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