How to plumb a Harman vf3000 Boiler

What is the best method to use when installing a coal boiler in line with a gas boiler? I read in the post below that you need to a a circulator pump between the two. Can someone elaborate. My oringinal plan was to to leave the zone valve connected to the gas boiler and just cut the supply line and feed it through the coal boiler, lower the temp on the gas boiler so if the coal boiler keeps the water temp high enough the gas boiler would never fire up.

http://nepacrossroads.com/post18562.htm ... 000#p18562
"I put my coal boiler BEFORE my oil boiler, moved my zone valves to the coal boiler, add a circulator pump between boilers, and I’m golden!"

You shouldn't have to change anything with your zones or zone valves. all that will still operate off of the gas boiler. You want to connect the hot supply from the coal boiler to the return of the gas boiler and connect a line back from the gas boiler supply to the return of the coal boiler. Use the 1 1/4" pipe. There should be a circulator on the supply side of the coal boiler.

There are several ways to do it, your best choice would depend on a number of factors. Parallel and in series are the two most common installs, they also can be isolated from one another. In most flow designs, I would urge you to use flow control valves. Bell & Gossett make a beauty.

Is your VF3000 a stoker or hand fired?
Do you want it to automatically switch to gas when the coal dies?
How do/will you heat your domestic water?
Does your gas unit have a stack damper?

The unit is a Stoker with a Domestic hot water coil, I would like the gas boiler to kick in if the coal fire dies out, and yes the Gas boiler has a stack damper w/ a blocked vent switch.

It sounds like I should connect the return (after the zone valves before the circulator pump) to coal boilers return, then the pipe the coal boilers supply back into the gas boilers return. In effect intercecting the return water and routing it through the coal boiler just before passing through the gas boiler.

I was planning on doing just the opposite, allowing the return water to pass through the gas boiler as normal and then picking up the gas boilers supply and routing it through the coal boiler before it runs out to the house. But I think that could cause the water temp to drop on the gas boiler before it get back to the coal boiler, and maybe cause it to fire up. Wow are you following this I think I'm confused.....

Is your VF3000 a stoker or hand fired? stoker
Do you want it to automatically switch to gas when the coal dies? yes
How do/will you heat your domestic water? the vf3000 in winter, gas in the summer if the coal useage is to high.
Does your gas unit have a stack damper? yes

I host a very similar Burnham with my pellet boiler.

I also chose to plumb in series just as you are thinking so when (not if) the pellet boiler fails the NG picks up the load. It was also easier - I use Teckmar ODR single boiler controls on each and am sure to set the NG control on a looser ODR curve than the pellet boiler for a lead follow team.

I chose to heat the NG boiler with the pellet boiler - just a way to look at it -and placed this contraption bypass for protection and balance - note the supply from the corn boiler feeds into the return of the existing NG boiler and the return of the NG boiler routes to the return or the corn boiler with a balance/tempering valve.

There is a control on the corn boiler that will halt primary loop pumping when supply drops below 145 - that allows the pellet boiler to idle in a non condensing mode. But when the house load calls, a small portion of energy is drawn away from the pellet boiler to feed the load - modulated by that balance valve. When the pellet boiler is heat soaked and on hi fire the primary loop pump defeats this open crossover and full temp water is sent to the load. If the pellet boiler cannot keep up to the load - and I usually have the burner off on the NG appliance unless its cold or I plan on being away for more than 8 hours - the Teckmar launches the gas boiler smoke damper that allows the gas train to fire and pick up the primary loop energy level. With out that Efical damper, there would be significant energy lost up the NG boiler stack.

Hope that helps - should work with coal as well and corn and pellets!

Kind Regards
Sting

ps -- please forgive the mix of galv and black fittings and scrap pipe - I did this on the cheep mostly with things I had laying around.

Coalbrokdale wrote:Wow are you following this I think I'm confused.....

Don't worry about that, I'm a lot more confused about it now than you are. More than likely, you will need the additional pump to do what you want. I hope you don't need this tonight. I want to think about it and then I'll draw something up for you.

Are there more taps on that boiler? Perhaps on the far side? I am assuming the flow is from the pump, through the bottom of the boiler, out the top to the house and return to the zone valves and back to the pump. Is that correct?

coaledsweat wrote:I am assuming the flow is from the pump, through the bottom of the boiler, out the top to the house and return to the zone valves and back to the pump. Is that correct?

Sure as long as you equate the "pump' as the primary loop to the bio boiler!Its really a simple quick install and it works - there are better algorithms - this one is the KISS install. An inexpensive blend of mechanical and automatic control.
The supply and return disappear behind the old Burnham to the other boiler room. Out of site is the loop pump and two more valves - turn those off and turn the balance valve full open - ant the system is exactly as it was when it functioned as a single NG boiler system.

How about this?

That will work with one pump. But the change over will be a manual operation with those isolation valves.

If you want an auto change over, you will need another pump and two of these.
http://www.pexsupply.com/categories.asp ... 7&brandid=
I will try and get a drawing up for you tonight.

That would be great I really appreciate it.

But if the VF3k runs out of coal then the gas boiler should kick on when it's low temp is reached, right? Then the flow would remain the same, just that the water would get pumped through the VF3k before it reached gas boiler. What the advantage of the valves you posted?

I think I get the idea.... "stops hot water from migrating into a zone that's not calling for heat. "

Coalbrokdale wrote:I think I get the idea.... "stops hot water from migrating into a zone that's not calling for heat. "

But wouldn't the pumps you have now for each zone already do that?

Coalbrokdale wrote:That would be great I really appreciate it.

But if the VF3k runs out of coal then the gas boiler should kick on when it's low temp is reached, right? Then the flow would remain the same, just that the water would get pumped through the VF3k before it reached gas boiler. What the advantage of the valves you posted?

If you don't pipe in a thermal break to stop gravity circulation - the flow controls will help limit thermal loss and zone overheat when there ins no call for heat from the load.

Sorry - didn't mean to jump in!

Ok so the Valve prevents thermal loss through conduction? I'll wait to see you drawing