Hot air venting into bus

daveola · April 04, 2018, 01:04:26 AM

I have a hot air furnace (Eberspacher Airtronic D4) I want to install into my MCI 102A3 and I'm trying to figure out how to run the heat into the bus so that it covers as much of the space as possible.

Fortunately my bus is only one room (no bedroom/door) so it's easier to cover the whole bus, but it's still 40 feet long and terribly under-insulated.

So - I'm tempted to just run an air hose along the wall with an outlet in the front and back, or possibly try to run an air hose through the luggage bays so it doesn't intrude on the floor space, though I worry about how much heat would go into the luggage bays (OTOH, some heat into the water bays on a freezing night might not be bad).

Another option is to run the heat into the floor ducting for the previous heat. I don't have the stainless steel heat runners that distribute the heat along the bus, but there are still 4 ducts in the floor that would hopefully get some of the heat, I figure I could somewhat cover the closest duct to push more air to the back ducts.

But the question is, would I just end up heating the ducts up which would be heating up the bays and underside/exterior of the bus? I don't get the impression that the vents under the floor are insulated very well, but they're a bit mysterious as to where they go.

Any suggestions on whether I should run hot air through these on a cold night, or if I should just cover them and run the heat directly into the bus?

richard5933 · April 04, 2018, 05:37:50 AM

Hard to say without more information about the layout of your coach and bays.

Our 4106 had ducting which ran through the bays and up through the floor in a few spots. I was not too fond of that set up, but it did make it easy to keep the insulated bays warm. Our current one has the furnace in the middle of the coach on the curb side. There is a 6" round duct going to the front and rear from it with a couple of outlets. The front run goes along the floor through the wardrobe (boxed in with plywood) and then under the couch where the outlet is. The duct to the rear goes under the side-mounted twin bed behind the drawers.

In my opinion, there are no hard rules on this as long as you have enough sq. inches of both inlet and outlet so that the blower can move the air properly. The manual should tell you how much your unit is optimized for. Remember that if you use flex ducting with a spiral wire inside it does act as a restriction and will adversely affect flow.

lostagain · April 04, 2018, 06:57:24 AM

And do put some heat in the basement. You never know when you'll have to drive through some freezing weather.

JC

buswarrior · April 04, 2018, 07:00:55 AM

What's the BTU on that D4?

Ditto, smooth pipe for longer runs.

Re-using stock coach elements saves the busnut from duplicating or otherwise building more stuff.

Mount the unit IN the water bay, and use the radient heat off the exhaust as an efficient trick to protect against a light freeze?

Happy coaching!
Buswarrior

daveola · April 04, 2018, 10:32:22 AM

Quote from: richard5933 on April 04, 2018, 05:37:50 AM
Hard to say without more information about the layout of your coach and bays.

That's part of what I was trying to figure out.

But I found the ducts in the part manual, and was able to figure out that the floor ducts go down to the blowers, and the air intake for the blowers is actually through the exterior of the bus. So that's a no-go - if I force hot air into those vents, some will just blow outside! It also made me realize I should figure out a way to cover those vents when I'm turning the heat on, though some fresh air in the bus is good.

daveola · April 04, 2018, 10:33:55 AM

Quote from: lostagain on April 04, 2018, 06:57:24 AM
And do put some heat in the basement. You never know when you'll have to drive through some freezing weather.

I'm hoping to be able to hit freezing weather, but only for a short enough time that I think I'll just put enough heat into the water tanks bay to keep them from freezing.

Though I'm tempted to put a water valve on the pump that leads back into the tank that runs occasionally when the temp gets low to see if keeping the water flowing will keep the tank from freezing.

daveola · April 04, 2018, 10:37:03 AM

Quote from: buswarrior on April 04, 2018, 07:00:55 AM
What's the BTU on that D4?

The heater is 4kW, which is about 13500 BTU.

Quote from: buswarrior on April 04, 2018, 07:00:55 AM
Mount the unit IN the water bay, and use the radient heat off the exhaust as an efficient trick to protect against a light freeze?

I've thought of that, but it requires running a fuel line all the way back to the water bay (my furthest back bay). Still considering it. Maybe a very low power heating cord wrapped around the fuel line to keep it warm during cold weather?

scanzel · April 04, 2018, 11:11:22 AM

13,500 is not much heat on a real cold night. Where is the unit pulling cold air from before it heats it and sends it on the way to the duct system. To get a fair amount of efficiency out of it you need to keep recycling the air in the coach through it. So basically you need a feed and return duct in the living area not pulling cold air from the bay area.

chessie4905 · April 04, 2018, 03:22:07 PM

On the GM's, the air intakes for hvac are about face high, one quarter to one third of the way back on each side. About 3x8 inches. Mesh with many approx 1/8 inch holes. Mounted in window style rubber. If yours are similiar, you can block them off with replacement solid panels made to same dimensions and installed in the rubber seals in place of the others. Or tape over to try first.

buswarrior · April 04, 2018, 04:31:59 PM

As noted, that's not a lot of BTU for messing around. It can be counted as a part of your cold weather defences, but not all of it.

The fuel line to it does not need heat protection. If it is that cold, you have bigger problems...

Do install a motor boat priming bulb in the line.

The waste heat off the exhaust is free, so running that exhaust pipe down thru the water bay has some benefit.

Mount the unit up high against the underside of the floor, intake a straight pull thru a hole in floor, output directed via piping into the coach directly above, and aimed wherever you think will help.

happy coaching!
buswarrior

oldmansax · April 04, 2018, 04:34:48 PM

My old '72 MC7 had the furnace piped into what I think was originally the return, the big duct that ran down the center of the aisle. Furnace was 40,000 BTU. It worked like a charm.

TOM

daveola · April 05, 2018, 03:26:19 PM

Quote from: buswarrior on April 04, 2018, 04:31:59 PM
As noted, that's not a lot of BTU for messing around. It can be counted as a part of your cold weather defences, but not all of it.

Sure - though so far we've lived off of two 1500W electric heaters even in freezing temps and survived, so I'm betting that the 4kW will generally make it warm enough - with the electric heat as a supplement when we decide to go winter camping.

Quote from: buswarrior on April 04, 2018, 04:31:59 PM
The fuel line to it does not need heat protection. If it is that cold, you have bigger problems...

I thought once it got to freezing temps the pump would struggle to suction fuel over 20-30' that I would need to put it back by my water bays.

Quote from: buswarrior on April 04, 2018, 04:31:59 PM
The waste heat off the exhaust is free, so running that exhaust pipe down thru the water bay has some benefit.

I hadn't thought of that - I was going to mount it on the floor of the bay, but it does make sense to save that heat in the exhaust. I need to make sure the combustion air intake is far enough from the exhaust so that it can run well, and there are some limits to how long those pipes can be, so I'll check into that.

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