they actually put good heat out when they're working correctly,, are you going to cromer? if so i'll have a look for you if you like.
if not heres what to do first.
take the grill off and gaffa tape completely over the fresh air vent to block it up.
make sure all 3 sliders on the heater controls are over to the right hand side.
look through the gap over the rear wheels and make sure the cable operated levers on the heater pods are fully forward (if not cable tie them forward)
provided the ducting from the alternator is in place this should give you hot air up the windscreen
this is the set up for a 2 litre Aircooled as you don't mention which you have