Vacation time spurs query about hot-water heating

Inspector's Eye

February 24, 2002|By Dean Uhler

A reader in Owings Mills has a 36-year-old American Standard cast-iron boiler that supplies hot water baseboard heating in his rancher.

The boiler appears to be set to add water to the system automatically if needed. His question is whether the main water supply to the house could be shut off during a winter vacation without damaging the heating system.

Turning the water off won't necessarily cause any problem with the heating system, but it would be more prudent to leave it turned on.

The system does not normally lose water while it's operating. For the system to lose water, there would have to be a leak or a malfunction that causes water to be discharged at the pressure relief valve on the system. You would probably know it if that were occurring.

With the water supply shut off, the lack of additional water for the heating system would be equivalent to the situation on some old hot water heating systems that were installed without any mechanism to automatically add water. On those old systems, water was added by the homeowner using a manual feed valve whenever it was necessary, such as when the radiators were being bled.

On the other hand, if the water supply was shut off and the heating system developed a leak in the basement during the vacation, all of the water might leak out of the system, leaving the boiler dry.

If the boiler "dry-fired" - heated up without any water in it - it would probably crack and you'd need to install a costly replacement. That isn't likely, but it could happen.

Another reason to leave the water turned on is so that water pressure in the supply pipes can prevent dirty water in the heating system from potentially leaking back into the drinking water supply pipes.

Although there is supposed to be a check valve on every connection between water supply pipes and a heating system to prevent this, those check valves are widely reported to be unreliable.

If the check valve doesn't seal perfectly, turning off the main water cutoff could lower the pressure in the water supply pipes enough for boiler water to flow into them, contaminating the drinking water.

The result could be intestinal upset from drinking the water if the pipes weren't flushed out sufficiently before taking a drink.

Inspector's Eye

Dean Uhler has been a home inspector for more than 12 years and is president of Baltimore-based Boswell Building Surveys Inc. Uhler is a member of the American Society of Home Inspectors (ASHI) and is the treasurer of the Greater Baltimore Chapter of ASHI.

Questions, with name, address and daytime telephone number, about homes and home inspections can be faxed to 410-783-2517, e-mailed to or mailed to Inspector's Eye, Second Floor, 501 N. Calvert St., Baltimore, Md. 21278-0001.

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