Here's a question...about heaters.

[Bub]

So, I have a reasonably well insulated 71' Bus, with upright T4 conversion, DTM, 411 heater boxes. And a Bn4 Heater that cranks out some serious BTU's.
Bn4 Heater is piped to the rear seat area mainly, and with a small bypass into the stock heat tube just in front of the engine. The 411 heater boxes are a mixed bag. They make hardly any heat, but keep the heads cool.
The real trouble with convenience in the dead of winter is actually getting the windshield de-iced, right? I mean, we can cope with the cold, but cant get anywhere if we cant see. And cant get any heat if you cant get the bus on the road and working a little harder than Idle.
So. I have a couple of those in-line booster fans (bilge type?). --You ever notice how much more air comes from the defrosters when you crack the window a little going down the road? --
The question is should I put the booster fan inline and try to boost the air up to the windshield, OR install it in the rear area to suck air out and into the engine compartment?
Seems like I may be fighting the pressure by simply trying to pump more air into the cabin when less is being allowed to leave- even with all the drafts around the doors, etc.
Any thoughts?
Bob O
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[Randy in Maine]

The bilge fan should blow, not suck. Blowing from the engine compartment will not induce a CO leak into the cabin due to a faulty heater box or exhaust system leak.

Plenty of air leaving around poor seals in the doors and windows (and westy windows, pop tops, sunroofs or whatever) so there is always a way for air to get out.

[Bub]

The thing is that even now the flow of air into the cabin from the defrosters is pretty measly. If I'm movning alittle and crack a window it increases quite abit.
So, getting some air to flow OUT of the cabin while stationary seems like it would be as helpful as trying to push more air in.
The suck / blow (no puns!) difference is only point of view. Its just moving air in a direction. Whether it 'pushes" warm air out of the cabin or 'sucks" warm air into it.
I may try one way or both to see what helps. I have nothign better to do do, right?
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[SlowLane]

Many moons ago I hacked up my '69 (Corvair-powered, so no "fresh-air" heat) to take the output of the gas heater under the rear seat, aim it at the input to a squirrel-cage heater fan yanked off an International Harvester pickup, which then blew the super-heated air into some household-type ductwork that plumbed into the stock heating tube (actually, I think at that point I had replaced the rusted-out central heating tube with a length of 3" ABS drain pipe). I used a hole-saw to cut a 3" hole in the floor just aft of the cross-brace, then worked a couple of adjustable tin elbows into the space, and wrapped it all up with duct tape. Ahh, those were the days...

I used a relay to control the fan. The relay was triggered by the heater control. Didn't have to worry about windshield defrosting after that. But my toes sure got hot with the flapper on the front tree flipped up.

On the intake end of the gas heater I took a big ole' ketchup can, pop-rivetted and duct-taped some more tin ducting to it, cut a hole in the back of the van to feed cabin air into the assembly, then sheet-metal-screwed and duct-taped the ketchup can to the inlet of the gas heater. Voila, recirculating cabin air. This was inspired by a neighbor's '72 which had a factory setup that accomplished the same thing (but without the benefit of recycling old tin cans).

'Course, that van (ok, "bus", jeez ) was pretty rusty, so it wasn't like I was hacking up a vehicle worth restoring, but I haven't had as much fun with a vehicle since...
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Present:
'81 Westfalia: 2L, manual. Originally Canadian, now Californiated
Back in the day:
'72 Super Beetle
'69 Camper Van - Corvair powered
'71 Window Van - Transferred Corvair from '69

"With sufficient thrust, pigs fly just fine." - Internet RFC 1925

"They say a little knowledge is a dangerous thing, but it is not one half so bad as a lot of ignorance." - Sir Terry Pratchett

[Duncwarw]

Bilge blowers are usually made of plastic. Plastic melts. Ask me how I know. Mine's in the engine room but the airflow is not great due to the bends in the ductwork I installed to feed the exchangers. Not to mention the noise. Even now, I can still just about hear it over the engine when it's on high.
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“To find yourself, think for yourself”
Socrates, 470 BC - 399 BC

[jeremysmithatshawdotca]

You could get some flexible dryer vent hose, hook it to the BN4 outlet at the back seat, and bring it up front. You can use the hose to defrost the window in the morning, then warm your tootsies as you drive. Even better, get some clear plastic, and seal off the front seats from the passenger cabin, and you'll have a much smaller area to heat with the BN4. My brother had a bus that had a snap in divider in it, and it got nice and toasty!

Jeremy

[steponmebbbboom]

[Bub]

[steponmebbbboom]

as I recall, Eberspacher did make a heater intake that did indeed draw from the passenger cabin. You have the early BN4 in the engine compartment, yes?

[steponmebbbboom]

ah yes, I remember now, steve_marriott:

[daves_ale]

[Bub]

Yes! I have the ducting just like you show, but unfortunately the placement of the heater doesn't allow me to use it-yet. I had to mount the heater waaaaay over to the left side of the engine to make room for the carbs- and kind of rearward.
It's a close fit and I'm really going to work on making that recirculating ductwork fit. My only regret is that the exhaust pipe fits so well, I'll have to cut / bend it if I move the body of the heater so I dont have to make another hole in the bus.
Looking atthe picture it would be a miracle to get the interior hole cut exactly where the ductwork lines up- its waay up in the intake in the engine compartment. Maybe do that part FIRST and mount the heater to line up?
Oh boy.. . here we go.
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[steponmebbbboom]

OK, what I would use in this situation is HVAC flexible ducting or spiral reinforced fabric duct hose. Do away with the plastic ducting altogether, and find a hose with a diameter matching your heater body, then simply mash it to fit along the path to the body intake. Flatten the hose completely on one side of the rectangular flange, then fold it over to wrap back around the flange, then use a long black tie-wrap to secure it to the intake flange.

Take the heater with you and check Home Depot, a commercial HVAC supply store (check yellow pages) or hydraulics shops. If they say no then ask them where to send you, someone will likely know.

[stevemariott]

The ductwork as shown by steponmebbbboom is great to have, but a total PITA to fit correctly if you have moved the heater at all (as you might have guessed). I moved my BN4 to the left and towards the rear a few inches so I could squeeze in dual DRLAs and I ended up cutting an inch or two off so everything lined up. If you can get it to fit so it functions as it should, it works better overall. I would try to make the heater fit as close as possible to the stock location so the recirculation ductwork fits in easier.

Just the other morning I finally fired my BN4 up - a very nice thing to have this time of year!
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1963 Manx copy
1968 Bus