Convection vs Radiant in Hydronic Radiators

Mike T., Swampeast MO

<I>In conventional, cast iron hydronic radiators (160-180 deg F. water temperature), what percentage of the heat output is through radiation and what is through convection?</I>

In a typical installation at least 75% via convection <I><B>while</B> the rad is heated to 160-180F during the heating cycle</I>. However that proportion of convection will decrease <I>when the boiler is not firing</I> as the radiator cools. It may also be difficult or damned near impossible to heat the rad to 160-180F in all but the coldest weather. BUT, as the radiator heats <I>to raise space temperature</I> its' proportion of convective output will increase. If that rad is however at just the right temperature to <I>maintain</I> room temperature <B>the percentage of radiation is maximized</B>.

<I>Does one size the heater differently if used as a convector vs. a radiator?</I>

Radiators are <B>designed</B> differently than convectors. You can use a radiator as a convector <I>if you raise the temperature</I> but it won't be as efficient at convecting were it designed to be a convector to begin with.

<I>How can one calculate how much a radiator is degraded in heating capability if a radiator cover is placed over it?</I>

Covers over radiators turn radiators into convectors! Unless designed as a convector it will require a higher temperature to achieve the same output.

J Kantar

Convection vs Radiation in Hydronic Radiators

In conventional, cast iron hydronic radiators (160-180 deg F. water temperature), what percentage of the heat output is through radiation and what is through convection?

Does one size the heater differenctly if it is used as a convector vs. a radiator?

How can one calculate how much a radiator is degraded in heating capability if a radiator cover is placed over it?

Thanks.