Converting a Steam Boiler to Hot Water 1

[Lorus]

A contractor just submitted a proposal saying that he can convert our 2-year-old cast iron sectional steam boiler into a hot water heating boiler.

Is this procedure possible and safe?

Thank you for any help.

 

[metengr]

Is the cast iron sectional steam boiler in your residence for supplying heat or is this for a client or business or to make process steam or……?

It sounds like it could be possible to convert a steam heating boiler to a hot water heating boiler.

Is it safe? Well, I would carefully review the contractors proposal in detail (what specific modifications are being proposed to the current boiler in terms of changes to operating pressure and temperature, burner configuration, output of hot water, storage tank, what standards or code have they referenced regarding the modifications, etc) and most important their engineering credentials and experience. I don't have a copy of ASME Section IV Rules for Construction of Heating Boilers to review at this time.

 

[Lorus]

Thank you for the reply.

I apologize for being vague originally.

The boiler in question is for a commercial heating system.

I am comfortable with the exterior aspect of such a switch, as I can redesign the piping and tanks etc as required, however my knowledge on the internal workings of boilers is poor.

To be more specific:

If the operating pressure of the new hot water system falls within the acceptable operating pressures of the steam boiler, are there any other reasons internal to the boiler that would make this switch a bad idea?

 

[metengr]

Ok. If this is for commercial purposes, most likely you will need to have this change reviewed and approved by the local Jurisdiction where the item is installed. Most likely, the local Jurisdiction will send an inspector out to review/inspect the modification, and issue an operating permit. This is the reason for my asking about residential hot water heating or commercial, because most Jurisdictions exempt residential items.

 

[TBP]

The boiler switch is typically the easy part. The piping & heat emitter bit where it gets tricky. Why are you considering changing from steam to hot water? Most steam systems can be made to operate very effecively for a fraction of the price of converting to hot water.

 

[Lorus]

Well, apparently the water in the area is of a very poor quality, and even with a professionally recommended water treatment plan the last boiler corroded out in a short 11 years.

It has been two years since this replacement, and the water situation has reportedly gotten worst, to the point where to keep conductivity under control 4 blow downs per day are required.

My initial reaction is the system must be leaking like crazy somewhere to require enough feed water to raise the conductivity so fast, however the building operators indicate this is not the case and the water is just that bad.

I am going to inspect the system next week to check on this.

Given all of the above, the conversion question was raised as being a possible solution.

Personally I would like to see the system fixed rather than a conversion, but if the water is that bad and if the operators push enough for it, the conversion will happen.

Altering the rads and piping I can handle, it is just the actual boiler part I an not familiar with.

 

[CRG]

What type of fuel is being used?

Make sure you do not have a problem with condensing flue gas. The steam boiler was not designed to accommodate condensing flue gases. If cooler boiler supply water is introduced with a lower operating temperature, condensates from the flue gas may be an issue.

 

[TBP]

What are the water conditions that make it "bad"? If this is a commercial building heating operation, you should be getting all (or very close to all) of the condensate back. This should mean that the water treatment issues would be pretty much non-existant. Do you have a meter on the make-up water supply?

Check your rads - not all steam rads lend themselves to being converted to hot water.

 

[kbs]

Every cast iron commercial boiler I've worked on has the info your looking for on the Boiler Rating Plate. If the boiler is rated for both steam and hot water, the rating plate will indicate the MAWP for each. If there is only a steam MAWP indicated, the boiler would have to be recertified for hot water apps.

 

[GenB]

Sec IV boilers for heating are good for 15 psi steam and 30 psi water design parameters, check the name plate to see if your boiler was stamped for 30psi water (as some are only stamped for steam 15 psi),
to change to water the level controls have to be raised to the meassure the llco to the top.
it is important that the llc-off are not disconnected at all; most states now require llc-off on all water boilers, thermosthats for oper. and hi-limits have to be added to control temperature, conrtrols for heating can be low temp to 140 deg F so 180 deg max. controllers are limits.
the contyractor have to be familiar with the ANSI Stds as well as ASME CSD-1 controls for water boilers.
It can be done but if not done correctly can be dangerous.
Hope this helps.
GB

 

[chicopee]

Cast iron sectional boilers are normally designed for either steam or hot water application. Check out the namplate and you will noticed that the boiler will have a rating for 15 psig or 30(or 40)psig. The 15 psig is the max. allowable pressure for steam and the other is for hot water. Obviously conversion will mean a change in the safety appurtenances such as low water cutoff devices, limit switches and and their settings, removal of relief valves on radiators, incorporation of an expansion tanks and additonal piping.

 

[Lorus]

So much great information here, thank you for the help.

I was unaware of the boiler stamp indicating if a boiler could handle hot water as well as steam. I will be sure to check that out.

 

[chicopee]

LORUS- ALL C.I. SECTIONAL BOILERS THAT I HAVE KNOWN AND SURVEYED COULD EITHER BE USED FOR PRESSURE OR HOT WATER FOR MAWP'S STATED IN MY ABOVE REPLY.