Have gas furnace,ac.adding outside wood furnace with 24v pump relay,installed heat exchange in furnace unit.Want to control air unit fan from both heat sources.would like to keep gas as backup.Is the best way to hook 24v lines from wood furnace to gas relay leaving gas connected also.If wood temp drops gas will turn on .But pump on stove will operate als0.Wood furnace maker recommends this.Or best to install 2nd relay hooked in series with gas relay on high voltage?