Nice work!  

In Finland we have been using electric heaters based on exactly the same concept for years.  Some guys use oil-burning heaters but I have an electric Defa car interior heater blowing hot air under the hood. 1,5 - 2kW is required for cold winter days. That's compact enough to be thrown on the luggage compartment for overnight trips. Getting the mains connection down there is an other story then :)

I had a cousin who was a mechanical engineer who designed and installed industrial heat and air handling equipment.  He gave me a couple of precautions on home-brewed aircraft heaters: Don't use an overly-constricted duct that will generate much back-pressure.  Most household heater fans aren't designed to "push" or pressurize air and depend on the free-flow of air to cool the heater and keep the heater and fan within a reasonable operating  temperature range.

He also advised that the duct be sufficiently long so the heater/heat source is not directly under the cowl - in the event of a heater fire, you won't burn up your airplane!

Looks to me that David's design meets those criteria!  Looks good!

Personally, I like the Hornet Aircraft Heaters, but they are defintely expen$ive!!!

John

N750A

I made one very similar to yours and added a day timer bonded to top of heater so start/stop times can be set. Works well for 10 yrs.

Here in SW Florida we use solar a lot. Sometimes too much! I like the ductwork on this heater you show-inginuity at work again!

What engine are you heating with it.

As I read your note, does it mean a) You built the thing in 30 minutes? or b) By running it, you had oil up tp green temps in 30 min?