Radiator stays warm

Scott Brown_2

Our house has steam heat and old radiators. The thermostats have recently been replaced and are turned all the way down, but the radiators continue to get hot. My heating company has been over several times and can't offer an expliantion. Is it possible that when the hotwater tank calls for heat, steam is going to other parts of the house? Any insight would be greatly appreciated.
thanks

Steamhead (in transit)

There should be

a limit control on the boiler called an aquastat, that stops the burner before the water can boil if only the tank is calling for heat. It's either missing or set too high.

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1974bobcat

You say you have hot water tank. If this is an indirect fired tank that uses the condensate water for a heat source you need some type of control to shut off the boiler before it makes steam. This is usually done with a strap on aquastat that is set to a temp around 160. This will prevent the boiler from overheating. The control just breaks the signal that is asking the burner to run.

BOB

Mike T., Swampeast MO

Are you certain they are steam radiators? I know that sounds like a stupid question, but many, many people confuse steam and hot water--especially when it comes to big cast iron radiators.

If the rads are connected by a single pipe and you see a thing that looks rather like a large bullet at the other end it's certainly steam. If you have little bleeder valves near the very top of radiators, it's almost certainly hot water and the rads will almost certainly have two connections to the system. If there are two pipes connecting the rads and no "bullet" or bleeder it's almost certainly steam.

It's certainly possible that heat could be going to the system during a call for domestic hot water--but such is NOT a normal occurance!

If one-pipe steam, the only way I can see much heat going to space heating during a DHW call is if the boiler is producing steam during that DHW call. This could happen if the DHW tank (or "tankless" coil) is vastly undersized compared to the output of the boiler. A clogged heat exchanger in the tank or coil could be the culprit as well. Presuming there's a circulator serving the tank (there should be), it could be defective. If the tank and/or tankless coil is fine and any associated circulator is fine as well, there really should be a control to prevent the boiler from firing above some temperature during a call for DHW well before steam is produced--typically 180F - 190F. Such control may be defective or it may have been "cranked" in an attempt to "get more DHW".

If two-pipe steam I'd say there's very good chance that it was originally a vapor system. (Other forms of two-pipe steam seem more common commercially.) If by some way the system is still producing steam at sub-atmospheric pressure (less than the normal boiling point at your elevation) you'd get space heating during a DHW call at typical supply temps. Even if not producing steam at sub-atmospheric pressure, vapor system [should] still operate at very low pressure and any of the problems mentioned regarding one-pipe steam would certainly apply.

If a hot water system, you could be experiencing gravity flow (sometimes called "ghost" flow) during a DHW call. Such would be most noticeable in a system originally designed for gravity circulation of hot water. "Flow-check" (e.g. one-way) valves can be used, but I'd suggest that the proper solution is a good primary-secondary piping scheme that prevents the flow before it can ever start... If it is a hot water, original gravity system and you have some reasonable $$$$ to spend and want to save GREATLY on your fuel bills, install a condensing/modulating boiler with the finest indirect DHW tank you can possibly afford.

If budget is very tight and the boiler is old and it's going to cost quite an amount to get things working right, and venting won't be much of a problem, consider a stand-alone water heater.

Leo

If it is steam

If it is a steam system raise the water level to the top of the gauge glass. I do this in my own home and advise customers with this complaint to do this also.

Leo