Converting Steam to Hot Water

ttekushan_3

This self balancing effect is wonderful. Where I work, we have a huge number of buildings with retail storefronts and one or two floors of apartments above. These are virtually all steam heated, with one thermostat or controller for the whole building. No zones. Whether the retail traffic is busy or slow, the storefronts quickly rebalance temps to the rest of the building.

Steam is drawn to the coldest radiators as you say, tipping the balance of steam delivery until the cooler rooms approach the set-point temp. Open a bedroom window in winter and watch what happens. That room will maintain almost constant temperature, and as soon as the window closes, one heating cycle will remove any temp discrepancy.

Steam heating is inherently a dynamic system, with the steam flow shaped and driven by the very space it heats. The environment of each radiator is what controls distribution, particularly at or near saturation.

For me, this is one of the joys of tuning up steam heating systems. To watch the laws of physics and thermodynamics unique to the steam heating method at work gives me a warm feeling inside.

I first noticed this many years ago when operating a business from a steam heated store front. My first winter there made me aware that something interesting and unique was going on in those pipes that I simply had to learn more about.

Soon I "adopted" the building's steam heating system and learned so much about it and tuned it, that requests for my steam services outstripped my original business demand. So I'm doing nothing but steam heating in the cooler months. AND LOVING IT.

-Terry

ALH_4

I'm seeking knowledge

I have noticed that the general consensus is that converting a steam system to hot water is not a good idea. Why is this?

From what I know:

There is a lot of debris in the system that can cause problems for a hot water system.

This makes sense as the steam system has been “breathing” and therefore oxidizing for decades.

There is a significant amount of piping that has to be modified incurring high labor costs.

This makes sense for obvious reasons.

Steam can be as comfortable as hot water.

With TRV’s, I could see this being close. I don’t think a steam system can ever approach the symbiotic relationship between a constant circ modcon boiler and the heat loss of the structure.

Steam can be as efficient as hot water.

I just do not see how this can be possible with modcon boilers and low temperatures in a hydronic system. Not so say steam cannot be efficient.

I haven’t worked with steam, so I admit my ignorance. I have read The Lost Art. It seems to me like steam was a wonderful way to heat when electricity was not readily available. Am I thinking in the right direction?

On a separate note: Why would anyone install a new steam heating system? I can see replacements, but what about new construction?

-Andrew

Brad White_152

Open Topic!

My gathering of the consensus and experience is as follows:

1) If you have an existing steam heating system, even two-pipe, but the boiler is shot and needs replacing, there is a risk of re-using the existing piping because of debris as you stated. It can be cleaned, it can be done but it is a toggle point where you could go either way. Radiator conversion, size relative to actual heat loss and need to supplement to meet HW temperature outputs would be the biggest obstacle IMHO in this scenario. My default absent compelling reasons to the contrary or other factors such as zoning, condo conversion or other splitting, would be to keep steam if at all possible.

2) Possible significant re-piping. Especially true if a one-pipe system. If a one-pipe system, I would say if the piping is in reasonable shape but the boiler needs replacement, keep it steam for sure.

3) If a working system is to be replaced on the premise that doing so and incurring all that expense will have an economic return by energy savings? Tough sell IMHO. If fuel cost was high enough to make that justifiable, they would be rioting in Tuxedo Park and the Hamptons.

4) Comfort- subjective. Something about hot cast iron that is hard to beat, but the eveness of reset-controlled hot water in oversized CI radiators is itself a treat. HW is more efficient and IMHO "more even", hence more comfortable.

5) Efficiency- Hot Water wins this one but not enough to change out a functional system for this reason alone as stated.

6) Why install one new? Matt MadDog!! Sweeney did for a number of good reasons, the least being to learn how it could be done. Super. The idea of a power outage draining all that water back to the boiler is a big consideration as Steamhead points out from time to time. And there is that subjective comfort thing, fast heating from proper venting and low pressures...

I see steam as a dying art. Knowing that it can be made much more comfortable than most people expect, I believe that a functional system needing a boiler replacement ought to be preserved.

There is room in here for decisions. I am responsible in my past ignorance for ripping out some probably perfectly functional steam systems and putting in good hot water systems. These could have been running today, and well, on properly designed steam. So yes, there is some atonement speaking here.

Jamie Hall

my two cents worth

being a convinced steam person... I run a lovely century old vapour steam system, powered by a two year old high-efficiency industrial Weil McClain boiler. I have no way of knowing whether my heating bill would be lower with hot water; I do know that the expense of changing over would have been horrendous.

On the comfort thing: steam -- at least vapour steam -- has a curious property I haven't seen mentioned. It is, to a great extent, self-balancing. That is, if one room is colder (for instance, if the wind is blowing hard), the radiator in that room will get more steam, making it warmer. Can't beat that. No moving parts... If the dead heads who put the thing in did it right (mine did) the radiators are properly sized to the rooms, and this will work. There is very little uneveness in temperature, as on colder days (when you need the heat) those great big cast iron monsters shed a nice even heat.

Just my opinion...

Steamhead (in transit)

And don't forget

that hot-water needs at least 10 times the operating pressure that steam does. If the system has any weak points, the higher pressure WILL do a great job of finding them for you!

For these and a few other reasons, our company does not recommend or perform this type of conversion, and does not work on previously converted systems. We don't want to be stuck as "the last one to work on it".

"Steamhead"

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Christian Egli_2

Here comes the steamroller

Who knew, this is a favorite topic.

Steam is the natural born heater, all the other schemes have to be artificially sustained in order to achieve comparable and acceptable performance.

While I think there is plenty room for everyone, whether you have electric ceilings, gravity hot air, combined forced hot air and AC, hot water baseboard, radiant floor, steam filled radiators, or you plainly live in Hawaii, each of these methods have distinct attributes where each is the ideal choice depending on your climate, your home, and your heating likes and dislikes. One solution for all times and all places for us to convert the world to does not exist. That said...

Steam heat has sided with several key physical aspects that give it superpowers that have long been the performance standards for others to match. Like the genie in the lamp, steam is ethereal and full of seemingly magical properties.

***

Steam heat relies on a phase change

This gives it a thousand to one advantage in heat ferrying ability. Trying to coax BTUs into small delta tees is as hard as making an elephant fit through the eye of a needle. But with lots of modern piping layout, lots of electrically powered circulators and a heavy hand of anticipatory control modules it is entirely possible to eat your elephant one bite at the time. It’s just that, with dining on a phase change from liquid to gas, you never risk a heat indigestion that leads to gross inefficiencies. (Chilled water storage develop the same strengths when going the water to ice transformation)

Phase change principles are proven the world over, everyday a bit more: look at your AC and your heat pump and your fridge. Air conditioning would amount to nothing without the powerful transmogrification . An evaporator where the liquid is boiled into a gas and a condenser where heat is radiated away and, the all important efficiency guarantor thermostatic expansion valves in between... like a radiator trap; the perfect air conditioning setup, the perfect heating setup.

There is no decline in worldly steam usage, district systems work best with steam, industrial needs are best served with steam, cooking is best done with steam... and homes are mostly fitted with the lowest upfront cost of the combined AC and forced hot air systems, of which the AC and efficient heat pump are both vapor cycles, just like steam heat is.

***

Steam is hot hot hot

Boilers grab a load of usable hot heat that burns off the fire. Obviously, if you limit your grab to 212F you’ll get a tiny bit less heat than if you scratch down to say, 100F. This is totally true and it is what most offends all those who want to dispel steam. But, is getting the most coldest heating fluid possible really a goal to seek? Yes, no, maybe. It depends? Ah? on what?

Mild mannered home owners don’t care one bit about their boiler; if they care about anything beyond the thermostat, they’ll care about the usable transfer of heat that occurs at the radiator. A radiator, not unlike a boiler, relies on a temperature jump for effectiveness. Hot radiators give effective heat, cold radiators give none. Just like in the boiler, big heat jump - big efficient transfer of heat, small tiny heat jump - incredibly hard to use energy for transfer purposes. The efficiency of a cold radiator is zero and it increases form that point on the more hot blooded it becomes.

Steam systems get away with smallish radiators, because they are effectively hot. Working the radiator with tepid water will decrease the radiator’s efficiency a lot - thus with low temperature, we play catch up by going to large radiant panels and for supreme effect, the radiant floor.

We have a boiler, we have a radiator, now we need a compromise.

A boiler and radiator combination is what our heating systems are comprised of and a modern boiler putting out heap loads of very low grade-near useless heat will make for efficient boiler operation but very poor radiator output. What a dilemma.

The opposite, a gas fired radiant tube will put out lots and lots of very high grade heat (but it isn’t the most practical thing to handle home heating and it’s firing operation isn’t as efficient as a nicely controlled boiler room combustion and it only works with gas). What a dilemma.

How about an ordinarily hot-hot water system? A good compromise between boiler efficiency and radiator efficiency - getting close.

How about a near cold modulating condensing boiler with super extensive radiation surfaces? Bingo. A good return for the money.

How about hot steam with boiling hot radiators? Bingo again. But this time, both up front installation costs and operating costs are considerably less than any system so far.

How about fully heat recuperating steam boilers and hot hot hot district steam temperatures? You hit the jackpot this time.

Mark Eatherton wrote an article in the current Contractor magazine about the wonders of downtown Denver district steam heat; he listed steam costs at $1.50 per therm and other energy at $2.50 per therm. Under such favorable numbers isn’t steam the obvious choice for heat? Consider that the cost advantage does not only come form temporary alternate fuel cost disparities (coal, gas, oil, electric), it mostly comes from souped up efficiencies with supervised boiler operation and super hot heating fluid. Neat. The city of Akron shows similar cost comparisons. Thanks ME, you must have known you’d make me happy!

***

Lastly, steam is smart... very smart

If it doesn’t like you, it burns you. This passive aggressiveness probably accounts for the some of the few enemies of steam, they got burned once and won’t learn... Remember however, that this aggressiveness is equally served on the cold.

Like it was brilliantly mentioned by Jamie and Terry in this post, steam goes from hot to cold, or more technically from high (or so) pressure to low pressure... and we find the lowest pressures always were it is coldest. Steam will selectively prefer the cold spots to go settle on; this is precisely why cooking with steam works best, it spreads the heat only where it is cold and neither ever overheats or burns the rest of the food. If steam works best for my broccoli, then steam radiators will work best for me.

The fantastic part is that steam does all this on its own. You don’t need any electronic patrol. You don’t need either an army of circulators and mixing valves along with any complex piping strategy. And if you add electronics to steam, it gets even better.

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I hope you haven’t run out of steam, yet.

I said earlier that other methods such as hot water can be made as effective as steam (sometimes even more so). So, what does it take to achieve these results? One serious loss of efficiency for hot water systems comes from when the high water mass inertia causes control problems that translate into costly and wasteful overheating.

Water, by nature, is heavy and lazy (hot air is even heavier and lazier, he he). It moves slowly and carries very little heat per pound. Conveniently, it is possible to whip it into shape by using forceful circulators (which you have to hire as extras and for which you have to separately pay their food in electric power). That takes care of the laziness.

To handle the overweight that water systems come with, there is only diet and exercise.

The system needs to be designed with as little water mass as possible - choose microscopic pipes, high delta t, low volume boilers, that’s the water weight reduced regimen. Next, since water has a hard time getting to move its heat around, a constant exercise program is called for, this is the constant circulation that is often spoken of as a fad. With this sort of therapy, a hot water system performs as efficiently and as effectively as steam, sometimes a little better, sometimes not.

Remember however that steam is swift and has no weight (a thimble full of boiled water fills the entire home). Furthermore, steam systems are built with big long pipes and cavernous radiators; these characteristics are ideally suited for swift and (near) weightless steam. Thus, converting an existing original steam system to run on heavy and lazy water will not ever work optimally. There is a total conflict of design parameters that no amount of exercise and no diet pill will ever breach.

But as I look outside, moving to Hawaii seems like a good idea. I imagine the cast iron beauties bronzing themselves to a tan on the beach. Seafood certainly tastes better there and that’s a good reason to go on a diet. It seems we’re debating the fun issues here.

Thanks for reading.

gerry gill

holy smokes Christian..

you obviously dont type with the one finger, search and destroy method..hehe

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