The old threads do have some interesting ideas but not much practical experience. It's nice to see the RV-500 has been used and gets high marks. On the other hand a G note for a water heater will put that project on the back burner so to speak
Also, if I replace the water heater the inline unit would have to go in the same place. It seems to me this is already vented to the outside so I don't understand the issue regarding carbon monoxide or oxygen depleation. I believe our '78 Argosy 24' has a six gallon tank and the RV-500 requires the space of a 10 gallon heater.
The Bosch seems to get nothing but negative reviews. I'm surprised because I've always thought of Bosch producing first rate, albeit expensive products.
The Excel sounds like a good option. Has anyone actually used one?
The previous threads bring up the CSA certification. It's actually CSA/US which means they used a CSA lab to do the testing and included all the US test requirements. It's very common to use CSA for "UL" testing and CSA has many test facilities in the US. There are a number of other labs which can also test to the applicable UL standard. This change in the safety testing buisness came about around 8-10 years ago and it's a very good thing. Previously it was basicly a monopoly market and service was slow and expensive.
Hard to tell from the advertising copy but it appears the Excel unit can be preset for a nominal water temperature. However, it won't adjust so if flow rates are varied a lot you might see some difference. Not a big deal to me, just need to be aware when someone is in the shower to a least warn them you're going to turn on the sink facet. Not a whole lot different that most homes.
Other brands I only saw passing mention of were names like AquaStar. The previous threads seem to mostly be over a year old. Tankless or On-Demand systems are slowyly gaining acceptance here in the US. I've seen them touted a Home Dopy recently and according to the Excel website you can get up to a $300 tax rebate. Their was also mention the Excel could be picked up on eBay for ~$300 which could make this a near zero net cost deal. Now that's getting down in my price range