Conversion from Steam to Hot Water?

Dave Wenstrup

All right Al. Let's get this baby humming. I'll call you tomorrow and we can talk traps, etc. But don't blame the steam main insulation--that was my job and I did it.

To all. Thanks for your responses and I will post again to tell you what a great job Al did.

Dave Wenstrup

Conversion from Steam to Hot Water?

OK, I am thinking about having my two pipe steam system converted to hot water. Why?

1. Efficiency – I have a massively oversized 1987 boiler with 75% efficiency before considering the very short cycles (like 20 seconds). Despite insulating every steam and hot water pipe, my basement is an oven. 30% of the house has been converted to hot water radiant floor heat, and I don’t think the boiler was resized.
2. Zone control, - It’s a big house, and we don’t use it all at once. I know that the efficiency and zone control will not save me enough in fuel for a reasonable payback period given the cost of the this project, but I am very concerned about global warming, and don’t like the idea of emitting 50,000 lbs of CO2 a year just to heat my house.
3. Well, and I say this with the utmost respect for the Dead Men, I just don’t like it. I have had steam and I have had hot water, and I like hot water. (I LOVE the radiant floor heat, but that is not an option for the rest of the house.) Despite a lot of work since we moved in last year, it still noisy and I still can’t get heat in my son’s room. My heating pro is no knucklehead either; he’s a real steam guy. The next thing he says I need to do change all the traps. I am not sure that will help, because the return lines aren’t getting hot. (OK, one was, but I still don’t get heat in my son’s room when I shut the inlet valve of the radiator with a bad trap). In fairness to my plumber and the Dead Men, we are working with a somewhat bastardized system. I think when the previous owner removed some of the radiators, they mostly capped the pipes at the location of the removed radiators, so we have some pretty long dead ends.

Anyway, for the reasons above, I’d like to convert. It’s a two pipe system, so that’s ok. I have 7 radiators and 11 convectors. The radiators are the hot water type, so I think they should work. So next I need to see if I have enough radiator capacity, so two questions: What's the heat loss of my house on the design day and How much radiator capacity do I have.

Heat Loss- I haven’t seen it calculated this way before, but this seems reasonable to me. Does this work?
• New York metro where I live had 3700 heating degree days last year.
• I used 4000 therms of gas just for heat, so I used 1.08 therms per heating degree day
• If I am using a 70 degree design day, I would use 75.7 (1.08 times 70) therms on my design day or 315K input BTU/Hour. My weighted average efficiency of the two boilers is 77%, so my Gross Output BTUs on the design day would be 243 K BTU. This should be the heat loss for my house.
• The radiant floor heating covers 30% of the square footage, but nothing on the top floor, so let’s say the radiators have to cover 75% of the heat loss. So I need at least 182 K BTU of radiator/convector heating capacity (not including the radiant floors)

So how much to I have?

• I have used the formulas for calculating the heating capacity of the radiators, but I have not seen formulas for convectors. The guts of these are cast iron with slanted fins. They are about 12” deep and 6” high and sit on 6” legs. They are enclosed in cabinets which vary from about 20 inches high to 37 inches high. How do I find out how much heating capacity these things would have with average 170 degree water?

If I do this, I want to do it right. I would completely re-pipe the basement and craw space get rid of any dead ends, and just use the old steel pipe that goes up from the basement to the radiators. Any other considerations I should think about?

(Sorry for the length and thanks in advance for your help.)

ttekushan_3

steam boiler rating

So your steamer is grossly oversized AND it can't heat. The rating means nothing. A combustion analysis and fuel flow rate measurement will probably tell you that the losses are huge. Far more than you imagine. And it may need new main vents, etc. But that oversized boiler with a couple of bad steam traps will "lock up" the air in the system and prevent full heating. All that boiler energy is being used to compress air in the system and heat the chimney (and basement). The giant red flag is that there's poor heat distribution and a boiling hot basement.

The system is screwed up by an inappropriate boiler, unsophisticated controls and some bad steam traps; all of these conspire circularly to practically double your fuel usage. Is this the basis of your judgment? A good boiler and a tune up will probably cut that fuel consumption in HALF. Spend some time around these forums and you will see that staged boilers and low-high-low firing of steamers running in Ounces of pressure have a mind boggling effect on fuel consumption beyond that, especially when utilizing thermostatic radiator valves.

That steam system is capable of very economical performance in the big picture. But not with that boiler. And not without someone who knows what they are doing.

I work in the steam business. I've encountered situations like yours. Most of the time I don't even replace the boiler and on average lower fuel consumption in circumstances like yours 45-50%. Cleaning, tuning and load matching can perform miracles. Boiler replacement is still necessary in many cases to achieve these results. But the results are real nonetheless.

I presume you are also aware that destroying very serviceable portions of the heating system which are capable of excellent performance pumps so much CO2 into the atmosphere due to the utter waste of the energy embodied in the remaining service life of the equipment? The current boiler is a pig so its replacement with something efficient and durable is necessary. In the end the fuel savings between your two options is quite small, but one choice will put more carbon in the atmosphere than can ever be recovered in fuel usage (such as it is) due to the nature and lifespan of the components proposed. The carbon footprint starts before a component's construction and ends only after it is recycled into raw materials.

And yes, I'm concerned about global warming too. This is why its good to look at the full product lifecycle and how what already exists in front of our faces can be optimized. Reduce-Reuse-Recycle. Its more true today than ever before.

-Terry

Steamhead (in transit)

There certainly are

First, with hot-water, you'll be running at least ten times the pressure you did with steam. This increased pressure WILL find any and all weak points in the existing piping and radiators, and the resulting leaks will damage your house. I've seen jobs where this happened and the results are not pretty.

Second, if any of those risers run in outside walls, you run the risk of them freezing and bursting in cold weather. The resulting leaks will damage your house.

Third, unless you do a proper heat-loss calculation, you will never know for sure if the radiators can handle the load with hot-water.

Our company does not recommend or perform this type of conversion, and will not work on a system someone else has converted. There are just too many gotchas and we don't want to be the last ones to have worked on it.

I would say with 20-second run times you have a control problem. And any good steam man ought to be able to get heat to your son's room and fix the water hammer. Thermostatic radiator valves can reduce steam consumption in rooms you want to keep cooler.

An old, oversized boiler will never be efficient either. No way, no how. But a new steam boiler properly sized will eliminate that source of waste.

So which is a better method of transferring BTUs from the boiler to the radiators? As far as we know, there has never been any scientific, head-to-head comparison of the two, in the same building using similar boilers and with both systems in optimum condition. We've been able to reduce some of our steam customers' fuel consumption by over 30%, without running any of the risks detailed above, just by getting the basics right. So why ask for trouble?

"Steamhead"


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Al Corelli_2

Been There

I am quite familiar with your house, Dave. Thanks for the compliment.

Yes, the boiler is large. I do not believe it is firing to its full capacity, however. Someone may have downfired it in the past. I have not checked this because we were going to change out the traps first.
The issue with your son's radiator is from a bad trap somewhere else. Again, we need to address this.
There is a new vaporstat, dirt pockets have been replaced, returns properly vented, etc.
The radiators need to have the traps checked/changed. And the option to install thermal operating valves needs to be addressed, as we discussed some months ago.
The steam mains in the basement and crawlspaces need to be insulated. Much steam is condensing in the mains and not getting to your radiators. The importance of insulation on the mains cannot be stressed enough.

Converting your system to hot water would involve very much work for very little, or more likely no gain. Using the old steam distribution piping would cause terrible leaks and service problems.

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Boilerpro_5

Short run times?

Is the boiler cycling on Pressure or the thermostat on those short run times?
You certainly should be able to get that system running better. Sounds like several simple things are out of whack.

Boilerpro

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Boilerpro_5

Uninsulated steam mains will certainly cook the basement

I have been in basements that about 1/2 the pipes were uninsulated and the basement was in the mid 80's or hotter. In fact people passed out in the basement due to the heat. After we insulated the pipes(even skipped the fittings) the basement now is in the mid to low 60's. It sounds like you still have some work to do.

Boilerpro

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Steamhead (in transit)

Now that we know it's Al

I'll say- listen to him!

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Steamhead (in transit)

And

take plenty of pics and post them here!

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