Well, the discussion has sparked quite a few ideas already for heating the lab, but I've had another one that might also do the job to provide the benefits of the Magical Heating lab virtue.
Instead of creating additional heat, as I've been focusing on, why not concentrate on more efficiently distributing the available heat? The lab already has two fireplaces (it's a fairly large lab). So why not use a Rego Ignem effect to distribute the warmth from the fireplace(s) throughout the lab directly?
Let's see how this could work. Base 3 is "Control a fire in a natural fashion (for example, control its direction of spread)." The guidelines mention that ReIg spells can control heat or light as well as fire, so this is the guideline I'm going to use. Radiating heat throughout a room is natural movement of heat, we're just enhancing it.
A good object that might be enchanted with such an effect at Touch range is an an andiron. I would say that for heat, Touch range means the object doesn't need to touch the fire, just be in contact with the heat of that fire. So a fire screen might be even better -- the closer it is to the fire, the more heat it receives and can distribute. The object itself would become hot, since it is moving the heat away from itself.
Effect: Base 3, +1 Touch, +2 Sun
I don't think there needs to be an additional magnitude to distribute the heat within the room (up to 10 paces), as this is a natural movement of heat.
Enchantment: Effect level 15, +4 for constant use (+1 for 2 uses per day, +3 for environment trigger) for a total level of 19.
Does that seem reasonable?
(The magus is better with Rego than Creo, so this is actually easier for him to enchant.)