Coolant Heater (Webasto etc) Sizing

[miscrms]

So I've pretty much decided to go hydronic heating and am trying to decide how big a burner we need. This is an uninsulated full size 40' bus, using the original bus heaters as the heat sources. Probably not going radiant floor heat at least for now, but may at least get the floor insulated this year. The combined strength of all the original heaters at full rated output is something crazy like 200,000 btu, and yet the Skoolie sized Webasto is 47,000 btu as I recall. Something there doesn't seem to quite add up. Plus we're planning to use a heat exchanger type water heater off it as well which will suck more heat out of the coolant loop at times. This will be the backup heat when its too cold to run the mini split heat pumps (or to supplement) though.

I started looking at a Webasto DBW 300 rated at 104,000 btu, but am wondering if I'm over doing it. They are pricey, and use more fuel and electric power compared to the Scholastic.

Anyone have any experience with various size units? I know there is another thread where someone is using a 32,000 btu Espar for radiant heat, blower heaters, and hot water which seems to good to be true!

Also just wanted to make sure that I'm correct in thinking that in the stock position the Webasto circulates heated coolant through the engine as well as the heaters. Nice because it pre-heats the engine, but another potential source of heat loss if you are just heating the bus and not going anywhere.

[Robin97396]

I've considered the same issues in the past and still remain undecided to this day. Previously I would have purchased the air heater versus the coolant heater, but at this time I'm leaning toward the coolant heater because of the ability to warm your engine.
You use the heater shut off valves near the engine block to control coolant flow when you don't need to be keeping your block toasty.

[Twigg]

Originally Posted by Robin97396

I've considered the same issues in the past and still remain undecided to this day. Previously I would have purchased the air heater versus the coolant heater, but at this time I'm leaning toward the coolant heater because of the ability to warm your engine.
You use the heater shut off valves near the engine block to control coolant flow when you don't need to be keeping your block toasty.

I don't think you can do that without some re-plumbing. If you just close those valves, coolant won't flow at all. Somehow you need to divert the coolant from the engine which will probably mean some new pipe and another valve.

[BlackJohn]

Originally Posted by Twigg

I don't think you can do that without some re-plumbing. If you just close those valves, coolant won't flow at all. Somehow you need to divert the coolant from the engine which will probably mean some new pipe and another valve.

I have to agree with you there Steve and besides why wouldn't one keep that block warm and ready to go in case of emergency. That is the hole idea of the Webasto isn't it?

John

[Twigg]

Originally Posted by BlackJohn

I have to agree with you there Steve and besides why wouldn't one keep that block warm and ready to go in case of emergency. That is the hole idea of the Webasto isn't it?

John

Well ... if you are staying in one place for several weeks you only want to warm the engine for a couple of hours before you move.

[BlackJohn]

Originally Posted by Twigg

Well ... if you are staying in one place for several weeks you only want to warm the engine for a couple of hours before you move.

That's fine with a toad on hand perhaps, but if not, always be prepared for emergencies. Cold weather is no friend to a sitting diesel at least in my climate type. Could cost you your life is what it's all about for me. Minutes count.

John

[miscrms]

I think it’s generally a good thing to have it flowing through the engine all the time, but it is another source of heat loss from the coolant.

It would be interesting to see a cooling system diagram. I’m unclear on how exactly coolant continues to flow through the engine when the heater loop valves are closed. I assume there must be a split and a bypass of some sort. But agreed I don’t think there is a way for coolant to circulate in the heater loop as usually set up.


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[BlackJohn]

Originally Posted by miscrms

I think it’s generally a good thing to have it flowing through the engine all the time, but it is another source of heat loss from the coolant.

It would be interesting to see a cooling system diagram. I’m unclear on how exactly coolant continues to flow through the engine when the heater loop valves are closed. I assume there must be a split and a bypass of some sort. But agreed I don’t think there is a way for coolant to circulate in the heater loop as usually set up.


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The engine thermostat will work with the Webasto running and circulate through the block and radiator when valves are closed as you describe.
Could be wrong but in theory...the Webasto also pumps.

John

[john61ct]

Keep in mind there are huge differences depending on a location's climate, Alaskan mountains vs just chilly sometimes.

Personally whatever I do will be thermostat controlled, so Going Big on capacity to handle touring ski areas won't penalize much being efficient in Texas.

And for a good hydronic system + HWS the bigger burner unit ends up not being a huge % of the overall price.

[TJones]

Originally Posted by BlackJohn

The engine thermostat will work with the Webasto running and circulate through the block and radiator when valves are closed as you describe.
Could be wrong but in theory...the Webasto also pumps.

John

Happy New Years Everybody!

The heater lines are usually plumbed off the water pump before the theromostat and return into the engine block. If they are closed coolant will not flow to the heater core in the bus. The coolant would continue to flow through the radiator with the valves closed when the thermostat opens.

I close the valves on my trucks during the summer to keep hot coolant out of the heater core. If I dont the AC cant keep up.

I think you would want valving to create 3 loops. Webasto to heater (cabin heating while parked), Webasto to engine (engine heating only) and webesto to heater to engine (cabin heating going down the road or parked engine and cabin heating).

There are some diagrams on the site if you search under "radiant heating". From what I read one must be carefull when using a heat exchanger between potable water and engine coolant because of the danger of the poisonous coolant leaking into the water.

Also if you are installing a radiant system with pex you must use propylene glycol in the pex with a heat exchanger to the engine coolant as the ethelene glycol in engine coolant will eat the pex.

Ted

[Robin97396]

Most people are using a tankless water heaters for their hydronic floor heat. Same coolant rules apply.

I don't quite understand how a webasto type coolant heater could be scaled down enough to power a hydronic heating system, or is that just through the heat exchanger? It seem like the scale is way out of wack. The floor system would take a relatively modest amount of coolant flow compared to the btu's the webasto is designed for. I certainly don't want to be heating my block continually considering the heat loss multiplied by the cost of diesel.

I keep wanting to get a diesel fired coolant heater for obvious reasons at this time of year. I'd like a heated floor but that doesn't fit my KISS theory or my luck with tech. Without a hydronic floor, how do I get heat out of the coolant? Yes people talk about using the bus heaters, and apparently the bus fans too? Those fans work from the start battery. Beyond that all I could think of was using bus heater cores to create a convection heater that doesn't require a fan.

[miscrms]

Just to be clear hydronic heating and radiant floor heating are two different things. Hydronic heating just means the heat is transferred via a fluid. Radiant flooring with coolant pipes is one way to get the heat from the coolant into the room. The bus heaters are basically just fluid to air heat exchangers plus fans. The fans can be wired to the house battery instead of the starter battery.

I don’t think there is an issue particularly if the diesel heaters being too big. As I understand there is a built in thermostat that cycles the burner to keep the coolant temperature in the vicinity of 160 degrees F. If the burner is significantly oversized I suppose you could have issues with an inefficient burn due to the duty cycle being too low, which could cause soot buildup and fouling of the injector.

You do want to be careful about using engine coolant in a single stage heat exchanger with potable water, as a leak could basically poison the water. But the marine/RV type water heaters I’m looking at are designed for that purpose, and I believe they use a dual stage heat exchanger that prevents contamination of the hot water in the event of a leak.

The main downside to the big burner is cost. The DBW 300 I’m looking at is $1700, but it is new/surplus. I can probably get a used / working Skolastic for about $600, so there is a pretty big cost difference.



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[TJones]

I have no idea how many peak btu you would need but it would probly be more efficent to run a smaller unit longer provided it can handle the peak load.

Ted

[miscrms]

I agree Ted. I got excited about the DBW 300 (moar power!) but the Skolastic probably makes more sense. Particularly as it’s a backup for the heat pumps. Plumbing it so we can close off the engine loop to preserve heat and using the smaller unit is probably the way to go.

I do appreciate the comments on being prepared for a cold start in case of emergency and agree. But in our case we will have a toad in case we need to get out quick for whatever reason.



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[Robin97396]

I have no plans for a heat exchanger for hot water. My granny used to tell me stories about people that got poisoned from poorly built heat exchangers back in the depression. I know they're safe now but it doesn't fit my KISS theory. Besides, guests don't use as much water if it's not on tap.

A diesel powered coolant heater would allow me to heat my block independent of the grid, as well as keeping me warm on freezing winter nights off grid. I am currently very addicted to the grid, with propane being my only heat source off grid. In the right situation being able to start the engine is invaluable. I'm planning to try to stay clear of those temperatures as much as possible. Like others have mentioned, there are occasional ski areas and other cold weather attractions at times. Propane is my only backup at this time.

[joeblack5]

For what it is worth... I use a webasto tsl17 in Elfie. I use the rear heater core under the seat and the front dash core. Elfie has some insulation.
The rear and front heater cores are in parallel and Teed into the engine block. I put the webasto under the bus and only have to close one valve to the engine to stop the flow. I increased the heater core in the rear and replaced the rear fan with large 12 vdc computer fans to reduce power consumption and noise and added a computer fan on the front heater core. These fans run of the house batteries. ( same as starter in my case) Without further insulation and better door seals it works well to 28F.
With a hardened lifestyle and some tweaking you could go a lot lower.
I was thinking about adding some heater hose inside the seats and may under the bed because that would reduce the KWatts needed.

Later J

[somewhereinusa]

Originally Posted by TJones

Also if you are installing a radiant system with pex you must use propylene glycol in the pex with a heat exchanger to the engine coolant as the ethelene glycol in engine coolant will eat the pex.

Ted

Do you have any info to support this? I can't find anything that says that. I have used pex with ethylene glycol with no problems.

There is a diagram of my system here as well as some info on the system.
http://www.skoolie.net/forums/f51/hy...eat-19412.html

It really isn't hard to build your own fluid to air heat exchanger using an automotive heater core and a muffin fan.

I can't speak of other brands, the Espar unit I am using, once turned on, cycles between high and low (not adjustable) depending on the water temp. I can say that down to temps of about 0 the unit cycles between high and low while keeping the inside temp about 68 or what ever I set the thermostats at. Meaning that I haven't reached the limit of the system capacity.

I have both radiant and water to air units once the inside temp is achieved, unless it's really cold, I don't turn on the blowers. The radiant heat maintains quite nicely.

For those contemplating not including the engine in the system, how will you get heat while driving down the road? If it's a great concern you can certainly add the valves to isolate it.

While the boiler itself has a pump it isn't big enough to pump through a complex system. I used individual pumps with thermostats to control the heat in each room.

Dick

[cadillackid]

Originally Posted by somewhereinusa

Do you have any info to support this? I can't find anything that says that. I have used pex with ethylene glycol with no problems.

There is a diagram of my system here as well as some info on the system.
http://www.skoolie.net/forums/f51/hy...eat-19412.html

It really isn't hard to build your own fluid to air heat exchanger using an automotive heater core and a muffin fan.

I can't speak of other brands, the Espar unit I am using, once turned on, cycles between high and low (not adjustable) depending on the water temp. I can say that down to temps of about 0 the unit cycles between high and low while keeping the inside temp about 68 or what ever I set the thermostats at. Meaning that I haven't reached the limit of the system capacity.

I have both radiant and water to air units once the inside temp is achieved, unless it's really cold, I don't turn on the blowers. The radiant heat maintains quite nicely.

For those contemplating not including the engine in the system, how will you get heat while driving down the road? If it's a great concern you can certainly add the valves to isolate it.

While the boiler itself has a pump it isn't big enough to pump through a complex system. I used individual pumps with thermostats to control the heat in each room.

Dick

**THIS**

is the way to build a heating system.. gives you both radiant and forced-air heat... the ability to heat the floor only solves one dimension.. on windy cold days the ability to directly heat the air is a must... he has both..

I used to run service calls for complaints of the heating system in a home being down.. only to arrive and find the radiant floor heat was maxxed.. floors were so warm your feet were on the verge of uncomfortablly hot.. and the occupants freezing because of it being a windy day and there wasnt enough heat transfer to the interior air to overcome leakage in windows / doors / fireplaces / etc..

whenever we would retro-fit Central A/C to one of these houses we also recommended adding some heat for that purpose..

I dont live in a bus so I cant say how similar that is when it comes to needs of air heating in addition to the floor heating.. but i would want the ability to heat both..

-Christopher

[miscrms]

Thanks all! Really appreciate the quick feedback. Based on the inputs here I pulled the trigger on a used Webasto Scholastic from eBay. Will still have decisions to make about hookup, but my first concern was picking a burner unit.

Dick, really appreciate you weighing in with your experience. Your documentation of your build is a big asset to the group, and part of what helped me decide to go this route in the first place.

We probably won’t have time to do a full multi-zone setup, but I am starting to think maybe we should just run the heater lines through the floor in a very basic combined radiant / forced air system. We’re taking up the floor anyway, and the coolant has to get from back to front somehow...

Thanks again everyone for all the help.

Rob


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[Robin97396]

This has been helpful. I sure do like the idea of having a warm floor. Using the heater cores as convection heaters seems like a natural. Putting water tubes all through my floor does not seem natural. You guys have got me actually thinking of making a hydronic floor heating system. I can't imagine what a pain in the butt that will be to install. It ain't going to happen this winter.

Weren't there some electric radiant heat floor heaters I read about a while back? I realize that's barely a step above putting a heating pad on the floor.

My rig is a "van" and during agreeable weather I can still empty this van out onto the lawn which would make installation of a floor heating system relatively easy.

My heating system for the past couple years has been to heat the air, which is why my feet always seem to be cold. Heat rises, so my head is warm while my feet are cold. No it's not diabetes causing cold feet. It's just cold feet because I didn't insulate my floor.