Converting steam to hot water

Chaz_6

I am converting a house from 2 pipe steam to hot water with 4 zones of radiators and baseboard and two zones of radiant. I would like to add a indirect but i am getting different answers on the size boiler to use I have a heating load of 162,000 btu and want to use a 80 gal. indirect i want to use a mod/con boiler some companys told 199,000 and some said,285,000 and last one 399,000 can some one help?

Mike T., Swampeast MO

Chaz:

I don't like to deliver bad news, but if the conversion you mention is anything like I invision, you are in for extraordinary expense to do it right and even then you likely won't achieve the energy savings that you expect.

Iron radiators sized for steam, baseboards (especially fin tube as opposed to cast iron) and radiant floors are a TALL order to combine in any system and frankly, I'd say that no mechanic worth his mettle would even consider such a combination in a new system. Since you want to convert from steam to hot water you WILL have a "new" system!

Insulate/weatherize the heqq out of the place and the steam rads will most likely be more than adequate under hot water but you STILL face the problems of conversion. The steam men whose opinions I most respect here essentially refuse to convert to hot water.

Two-pipe steam systems, in general, were the Cadillac of steam and while they'll never be as efficient as the best modern hot water systems, they can and do operate with system efficiency better than many hot water systems. Thermostatic radiator valves (TRVs) can be installed to allow room-by-room "zoning" at a surprisingly reasonable cost.

I don't know where you're located, but check "Find a Contractor" here and seek out the FINEST steam man available. If you're uncertain about how to evaluate a steam man, buy Dan's books (available here) "So We've Got Steam Heat" and "The Lost Art of Steam Heating". Study a bit and you'll know the proper questions to ask and you'll find the tiny amount of money spent on the books to be the best investment you've ever made.

Steamhead (in transit)

I agree

don't convert it.

Besides the issues Mike mentioned, you'll be running those old pipes and radiators at over ten times the pressure the steam ran with. If there any weak points this increased pressure WILL find them, resulting in leaks. I've seen buildings where this has happened and it's not pretty. Liability lawyers love cases like these.

I'm one of those guys Mike mentioned. My company does not recommend or perform this type of conversion, and will not work on a system someone else has converted.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

nicholas bonham-carter

HIGH PRESSURE WOES!!

remember the difference between the original design operating pressure of early steam systems of 12oz. and compare that with 30psi[480 oz.] could any one stand 40 times more pressure?--nbc

Bruce M_2

What Boiler?

What kind of boiler is there now? You should leave the steam system intact and heat the radiant system with a separate boiler.

Chaz_6

What trouble is common with mixing zones with radiators and zones of radiant?

Mike T., Swampeast MO

Four mixed zones of standing iron and baseboard (is it fin tube and at least two stories?) and two radiant zones in an old house (kitchen and bath?) is a tough order.

With a mod-con in particular you want to keep your average system temp as low as possible given the emitters. Ideally, all of the emitters will operate at the same temperature. All mod-cons further lower the average system temperature by some form of reset. The warmer the weather, the cooler the average system temperature. This results in a heating curve.

Heating curves vary, not only by weather, construction, etc. but also by the type of emitter. Idealy, all of the emitters in a system will also operate with the same general curve.

Provided you've insulated and weatherized reasonably, your highest floor rads are now relatively oversized. Hot water systems had significantly larger radiators and subsequently, the effect wasn't as noticeable, especially if the uppermost heated floor has a full attic above.

Should one of the desired radiant zones be the kitchen, be aware that kitchens are a common trouble spot (particularly in older homes) combining a lack of heatable floor space with an abundance of loss from windows, doors, poor insulation, etc.

Your mix of zones and emitters could easily require three different temperatures and even if they were sized for design output at the same temperature, they would almost certainly operate at different heating curves.

Provided a reasonable balance can be achieved among your various emitters and zones, some mod-cons can control multiple temperature and multiple curve systems via mixing valves. Such systems are proprietary and expensive. For other boilers, suitable control systems with proprietary thermostats, mixing valves, reset, etc. are available and are also expensive.

Thermostatic radiator valves can be used with a two-pipe steam system and unlike one-pipe systems do not require a vacuum breaker. They allow individual room temperature control so in effect, each room is its' own zone.

When filled with circulating water, your steam system will unleash a torrent of rust, scale and other crud. Space was intentionally left in most radiators for this accumulation. The very idea of cleaning such a system gives me groans for a conventional, cast iron boiler and shivvers when connecting it to a mod-con and expensive, motorized mixers.

Personally, I would only consider such a conversion if all of the radiators were removed to the outdoors, pressure tested under at least 50 psi, cleaned thoroughly with all or nearly all of the piping replaced. In other words, completely tear the system and recycle the rads that don't leak. This is why I said "extraordinarily expensive".

Find a good steam man. If you have ready access to anthricite coal and your two-pipe system was originally a vapor system, I suspect that one of our finest steam men could restore original modulating operation with the Coal Gun Boiler