Cabin Heat

So as mentioned in a few places we escape the cold of the North East several times every spring and head for sunny Southern states. But, we do have to live in the coach while we travel, and sometimes it takes several hundreds of miles to get out of the polar conditions. Elsewhere I have addressed what I do to keep the plumbing from freezing, but more importantly I need to keep the people from freezing.

The business end of the coach is taken care of. The dash heat is quite adequate, and especially with the cockpit curtains closed I can control it just fine. I can’t say the same for the cabin. The dash heat will not keep it warm. Now, if there’s just two of us my bride can be up front and warm. When we pull over we crank the furnace and the cabin quickly heats up. But sometimes she wants to sit in the back, and sometimes there are three of us and one or two people sit in the back.

Some furnaces will run when driving, ours will not. I suspect the airflow around the intake/exhaust area is such that it blows out and cannot restart. After three tries it gives up. So, the alternative is electrical heat. The heat pump does quite well, and the noise is not an issue while driving. But, at about 40ºF it starts losing effectiveness. The fireplace works well, but 1500W is not enough to keep it warm back there when the temps are at freezing or below. And, both these require the generator to run, which I have no problem with, but it would be nice not to have to.

Then….. I figured it out. There’s hot water running right under the floor. Like any other car (except an EV like a Tesla) the dash heat is a simple radiator through which hot water runs, with a fan blowing over it to extract the heat and warm the air. Ducting and baffles direct the hot air to where we want it. The hot water comes from the cooling system of the main engine. There’s a supply hose and a return hose that run all the way from the engine to the front of the coach and back. In fact there are two shutoff valves in the loop by the engine which are mentioned on the radiator fill procedure on the sticker in your back engine bay. You can tap into this hot water loop! In fact that’s how auxiliary heaters in school and other buses work, as well as the auxiliary heaters in Suburbans and larger vans.

So….. after much measuring and figuring I ordered this:

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About as simple as it gets. Small radiator, two hose connections and some 12V for the fans.

So, where are these hoses? Warning…. high risk of very dirty hands and arms, bruises and cuts. As I am increasingly learning that getting to ANYTHING on the engine is tough, very tough. But, I had a starting point. I got under there and I found the two valves that looked like they could be in the heater hoses.

The first one is on the left side about a foot and a half in front of the radiator on the inside of the frame rail. The hose comes out of the bottom of the block, so that’s coolant. The silver tubing you see in the bottom of the picture is the air cleaner. (Notice theres’s a drain next to the valve.)


The next one was hiding a little better, but I did find it. Look waaay up between your two fuel filters:


Now…. to find a place where I could tap in, preferably close to where I could install the heater upstairs in a good location and get to it. Long story short…. the bed box. Plenty of space to mount it, and two holes down through the floor would lead to the area right above the axles, which is clear and unobstructed. It’s also the place where all hoses and wires go into the channels that run to the front of the bus.

So, now to figure out where the hoses go into the tubes. (This is where the cuts and bruises come in) Since you can’t see much you have to feel your way over the transmission and around the engine to follow the hoses. And there’s a curve ball, as you find too many hoses….. Until you realize that two of them are the DEF heater. (Internal to the tank). So, there’s two supply connections on top of the engine. The hoses wrapped in silver heat shield. One runs to the DEF tank and then back OVER the tranny down the left side back to the bottom of the engine on the aft end. The other runs down to the right side to the valve (above the fuel filter) then forward, over the transmission, and then forward into the channel. The one from the left side to the valve runs forward and then meets it’s buddy and goes into the channel. So….. I was pretty sure I had the two heater hoses in a spot where I could easily tap in, and run up to the bed box. But I had to be sure. Also, I wanted to know for sure which one was supply and which one was return as I wanted the heater in the return and keep the hottest water for the cockpit to defrost etc. So I started the engine, and ran it until the air out of the cockpit heater got warm. Then I shut it down and felt the two hoses I had identified. BINGO. What I thought was the supply and return were indeed warm, the supply warmer than the return. The red tape is on the supply. The return is right behind it not visible in the picture. The air bag is the left rear suspension, you can see the left rear shock, the axle at the bottom and the back of the inside left rear wheel.


WARNING: There are two hoses that look JUST like coolant hoses that go into the right side channel. If you follow them aft you come to the power steering pump on the right bottom of the aft end of the engine. Needless to say you do NOT want to cut into these.

Then it was a matter of splicing in. I cut the return line (YEAH, coolant coming out….) and made a pretty splice with shutoffs and a bypass. The reason for this is that when it’s in the 90’s and you’re fighting to keep the bus cool you do NOT want a 220º metal box under your bed. And, if it ever springs a leak I can also bypass it. BTW the two “Y’s” came with the heater. All hose is 5/8″. Valves are 1/2″ pipe, with 1/2″ pipe to 5/8″ barb connectors. Home Depot or Lowe’s….


After that it was a matter of two holes in the floor and up into the compartment under the bed. I think it’s a VERY good spot. The exhaust is aimed down the hallway where it will keep the bunk room hot, the couch area warm, and enough of it will get into the half bath. Also, I put a return on the back side of the bed so there would be some circulation over the bed towards the back which would spill into the aft bathroom.


Lastly the thing needed 12V for the fan, and a spot for the fan switch.