We have a 2009 31FS, which has 2 slides. The back slide has 2 bunks opposite the bathroom and the back bedroom is next to the bunks. Our motorhome has 1 heating vent in the front half of the motorhome, under the kitchen sink. In the back there is 1 in the bathroom, 1 in the back bedroom and 1 in bunk house. So there is a total of 4 heat vents.
The front half of the motorhome stays warm enough, however the cab over area is usually a few degrees cooler than the rest of the motorhome. The back half of the motorhome in my opinion is too warm. The thermostat is right by the entry door in the front half of the motorhome. Since there is only 1 vent up front, I feel the heat runs longer than it needs to, making the back half warmer than I like it.
I wish there were 2 up front and 2 in the back, that would be more balanced. I think the vent in the bathroom is a waste. The bathroom door needs to be propped open when the heat is running, otherwise the bathroom would be unbearably hot while the heat is running. Our furnace is in the bathroom, hidden in a cabinet next to the bathroom sink. That makes it pretty much impossible to re-route the bathroom duct.
With the thermostat set at 70, the back of the motorhome usually warms to about 74 - 75 by the time the thermostat kicks the heat off. That's way too hot for me, but it keeps the wife happy.
-Michael