Can anyone tell me whether these vent free heaters from Rinnai are any safer than your typical wall mount vent-less heater from Northern Tool or some-such place. I live in a late 1800's home in the far northeast, and while I have had it well insulated, I'm pretty sure it isn't anywhere near as "tight" as newly constructed homes tend to be today, if this makes any difference. Was considering one for supplemental heat, but wanted some input as to whether these had the same drawbacks as other, cheaper vent-less propane heaters. thanks.....tony