I am currently constructing an RMH in my greenhouse, however I became too enthusiastic in creating the channel under the floor and now do not have enough power to force the exhaust through. In this case I have installed an old computer fan which runs off of my gardens solar charged system. This works amazingly. However i would not be willing to use such a system in a house. However much building regulations are an annoyance, the basic principle is to avoid integrating a possible death trap into the design. It seems to me that what you are proposing is the possibility of gassing your household in the case of failure. Regardless of an alarm (electric failure would require batteries, who will remember to check and test?) these systems when developed properly work safely with out assistance. Why complicate matters?
I would suggest following the advice of the others above rather than inviting a darwinian solution to your suggestion.
Ps I will be back to ask for advice on solving my heater problems once I have spring out of the way.
