steam or hydronic?

[mgbinspect]

The way it was explained to me many years ago by my mentor was that the open system on an original gravity feed had no resistance and allowed the flow of cold to hot/hot to cold without any impediment. The moment heat was applied to the water in the boiler it started to move. The water expanded (heat rises) to the attic overflow and moved freely with the slightest amount of heat.

It truly is amazing. I've run across quite a few gravity hot water systems here. With the first few, I expected them to take their sweet time getting all the radiators up to temp, but I've never experienced an appreciable difference between forced and gravity systems. Pretty cool.

The pressure head deal is a bit hard to imagine. One would think that, pressure or not, the heated water would still want to move, but as I've already demonstrated, my understanding of hot water heat is pretty elementary.

[Phillip]

I am glad I don't have them in my area. I have seen a few old steam setups that was no longer in use, but not a live one.

[kurt]

Make the pipes big enough, and gravity heat works pretty good either way.

I don't consider myself a guru by any means on this stuff......I know a fair amount about steam and old hot water systems, though. We got a lot of them, and they're fun to inspect. Way more fun than forced air.

[Bill Kibbel]

First, I am talking about gravity hot water, not steam. The two are not closely related.

I mentioned steam only in regards to the primary systems they're most often asked to speak about at conferences.

I am not sure who your guru's are and how much gravity hot water they dealt with.

There's a mechanical engineer that designs rather complicated hydronic systems for commercial and industrial applications that also has spec'ed many conversions on historically significant buildings. There's also an experienced mechanic that I met at an historic hotel restoration project. We were both brought in as consultants to troubleshoot some issues. He's a top expert in hydronic systems and also an experienced expert witness.

The way it was explained to me many years ago by my mentor was that the open system on an original gravity feed had no resistance and allowed the flow of cold to hot/hot to cold without any impediment. The moment heat was applied to the water in the boiler it started to move. The water expanded (heat rises) to the attic overflow and moved freely with the slightest amount of heat. The addition of an expansion tank and pressure relief valve created a "pressure head" that the gravity flow action had to overcome. Water did not move as quickly. It (heated water) had to get to a temperature that allowed movement against the pressure head especially without a forced movement from a circulator. With a pressure head and a restricted water flow, it took longer to get the same results.

Adding 12, 18 or 24 psi of pressure in a typical residential system has absolutely no significant effect on head pressure in this application. In fact it was found by closing the system, the temperature of the water could be increased. If you studied these systems and researched this topic, you'd know that the hotter the water, the faster it circulates.

(My guru on hydronic and steam was Tom Byrne, now deceased, but one of the best and most knowledgable guys dealing with wet heat.)

I've met Tom a few times and know of his plumbing and inspection experience. Do you have anything that he, or anyone else that is credible in this area, has written to back up your original statement?

This was something I subsequently confirmed by my 30 plus years inspecting in a wet heat area with many gravity feed systems some of which were still burning coal.

Well, I've only been at it for 24 years, but my experience (inspecting over 11,000 buildings built before 1900 also in a wet heat area) has never shown that in a gravity system "The natural flow of water, (cold to hot) on an open system worked/works better than the same system closed".

If I'm wrong, I'd sure like to know. Please show us something from a credible source.

[ghentjr]

Originally posted by ghentjr

Well, I've only been at it for 24 years, but my experience (inspecting over 11,000 buildings built before 1900 also in a wet heat area) has never shown that in a gravity system "The natural flow of water, (cold to hot) on an open system worked/works better than the same system closed".

If I'm wrong, I'd sure like to know. Please show us something from a credible source.

I obviously do not have anything like a "credible source" except for what I wrote. I have only what I stated, and what I observed through experience. But I will tell you that in my opinion closing a system without a circulator produces a less efficient system.

But I would not argue with someone of your obvious knowledge and experience and I would bow to your expertise.

[Neal Lewis]

John, does it make it less effective or less efficient, or both?

I've seen a lot of the gravity systems, but I've never seen one that was converted to a closed system without adding a pump to it.

[Tom Raymond]

What kind of water temps are these things running at?

[ghentjr]

John, does it make it less effective or less efficient, or both?

I've seen a lot of the gravity systems, but I've never seen one that was converted to a closed system without adding a pump to it.

Good question. If it takes longer for the higher floors to get to temp it is less efficient, but it will get to temp so not less effective. Around here these were frequently converted without circulators. Much cheaper to do.

[ghentjr]

What kind of water temps are these things running at?

Most around here were set at 180 high limit. But they probably would work just as well at lower temps. It is my understanding that 150 probably would be efficient. Remember, these systems did not have hot water coils.

[genduct]

New here and glanced at some of replies but,

the gauge pressure is set high enough to get the water to the top of the system plus a little more 2.31 ft/ psig.

Not only warm air ( the other fluid) but hot water also rises and cold drops so the gravity systems have been working without pumps for years. The inefficiency is offset by the mass of the 'iron that is hanging off them and the boiler doesn't cycle as much as you might think. In the early days they had trouble making pumps and gaskets that could handle the heat so pumps weren't just expensive but also a maintenance problem. Also the reason why they were on the return side And finally if you do have to be careful with return temps too low since the products of combustion are CO2 and water. Don't want to try to make a standarrd boiler become a condensing boiler since it then will rust to nothing. Any help?

[MPdesign]

When I look at Boilers (to determine if steam or heated hot water) I look for:

1) sight glass

2) Pressuretrol

3) Water pumps

4) Steam Traps

5) Heat exchangers

6) How is the hot water there generated?

It can be very tricky. I have never seen a system like you have there...

I have seen steam boilers used in heated hot water applications.