Boiler pipe sizing question

Wayco Wayne

wants to repipe their 20 year old cast iron boiler so they can add and indirect, a panel rad loop, and a baseboard loop to the existing Cast iron radiator heating system. The heat loss of the house is 65,000 btuh, but the boiler is rated at 150,000 btuh. Do I size to the boiler in place, (which may be upgraded in the future to a closer size to the heat loss) or do I size to how many btu's I'm moving? WW

<A HREF="http://www.heatinghelp.com/getListed.cfm?id=255&Step=30">To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"</A>

kevin coppinger_4

I almost always...

do headers in 1 1/4"...its only if I exceed 140,000btu that i go up to 1 1/2...kpc

Wayco Wayne

Gee

I was thinking of going down to 1". The load is far under the 80,000 btu limit for that. I was just wondering does it affect a cast iron boiler to not have as much flow. I guess I'm used to the Munchkins where there is a definite low limit to flow or you have problems. To lessen the flow through a cast iron beastie I would think it would just act as a buffer tank and store btu's. It's going to short cycle anyways because the load is so small compared to the boiler size. Am I thinking clearly on this? WW

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Unknown

yes, you are

The thing that changes when the flow rate changes is the difference in temperature between the hottest part of the boiler and the outlet temperature.

The hottest part is right over the fire, against the iron. as the flow rate slows down, this spot becomes hotter, and the actual temp is determined by the starting temp (return water)

If the water is coming back pretty hot, and the pressure is low in the boiler, and the pump / expansion tank relationship isn't correct, or some combination of these, these hot spots can flash (or thump) into steam pockets, that don't show up as high temperature on the gauge.

Opening the bypass a little more takes care of this. Pipe the supply and return full size for the boiler BTUH output at least up to the bypass.

Noel

hr

You really

don't want excessive short cycling. Doesn't take much to add a buffer tank to prevent that, until you sort out the correct size equipment.

Pipe sizing depends on the delta t you decide to run. Most boiler manufactures will dictate allowable T through their boilers. I would guess 20 degree would be safe for most cast, makes the calcs easy!

Some German boilers claim to run fine without boiler pumps! I suspect if yours is 20 years old it is not one of those

hot rod

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Wayco Wayne

Thanks guys

I always think of using an Ergomax as a buffer tank. Can this be done? I'll try to look up their web site and see what they say. WW

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

hr

Sure

an Egromax is one way. Not the cheapest tank on the market, however It would buffer and provide dhw nicely.


Siggy did a column recently on a contractor in Alaska, Mike Reif, I think, that buffers with Ergomax "Signiture Systems" I think. Check the www.pmmag column archive for the article and his piping arrangment.


hot rod

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Wayco Wayne

Hey Hot Rod

You say Ergomax is not the least expensive. Are there alternatives that serve the same function? Sure you could put in an indirect and a buffer, but that is space that can not be spared in this case. One footprint is all I can afford for the domestic.

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Joe_13

The article is here

http://www.pmmag.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2379,78589,00.html

This is the design bible I want to follow on my system upgrade. The Turbomax reverse indirect is out of Canada. I want to use the Dunkirk Artesian tank (hopefully cheaper!)
Other reverse indirect sources: www.tfi-everhot.com
Laars also has the Duraflow.

Wayco Wayne

Thanks Joe

The article is most excellent. I will be checking the other inside out water heaters after the holiday.

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Mark Eatherton1

I've always told my students...

to size the near boiler piping to the load and flow, and don't just use 1-1/2" ppie because thats waht the tapping size is.

Many manufacturers use the same end section configuration regardless of whether its 3 sections or nine sections.

Size to the flow, and if you're using a 30 degree delta T instead of a 20, the pipe will probably end up being even smaller.

ME

Joe_13

You're welcome WW

Strange thing about the ErgoMax units: The smaller E23 and E24 tanks look better suited for residential size boilers, but only have 1" boiler and 1 1/4" domestic water connections. Seems backwards to me. The Artesian has the smallest 18" wide footprint. I haven't figured out how to work a Tekmar 260 control and sensors in for outdoor reset, DHW priority, and Warm Weather Shutdown when you have the tank on the primary loop and the boiler circ is also your DHW circ which must be running whenever the burner is firing.

kevin coppinger_4

riddle me this....

why does Buderus on their 115-28 oil boilers have a 1" tapping on the return and a 1 1/4" tapping on the supply? This boiler ibr is 85,000btu, doe is 98,000btu...why is that? Generally speaking 1" max @ 20*D T is 80,000....how do they "get away" w/ that...kpc

Mark Eatherton1

Care for a cup o'

Delta Tea? Pull up a chair, make yourself comfy and I'll spin ye a yarn about 20 Degree Delta T...

It only happens in an engineering sense, and RARELY does it actually occur in real life. I think I've seen it once, and that was on a SUPER cold start up in new construction.

The Germs dance to a different delta T tune. They look more towards 30 to 40 degree differentials, which equates to a MUCH slower water flow. Hence the 1" return. The larger supply is to aid in air elimination and removal. The boiler is where the water will be hottest and slowest, and where air has a greater potential of coming out of solution. Once your thru the air elimination process, it
s perfectly acceptable, in fact preferable to drop down to 1".

Need some sugar for that Tea? :-)

ME

kevin coppinger_4

well...

thanks for answering that for me, ME ...I have ALWAYS wondered why that was! kpc

Wayco Wayne

Joe

I looked into some old Ergomax piping diagrams and found one that had a swing check valve in between the take off tees for the secondary circuits. This meant that you could run the secondary loop without running the primary circ because the differential between the tees would cause flow through the primary circuit, and by default, the tank. When the tank cools down 20 degrees or whatever the differential of the water tank control is, it will bring on the boiler and the primary circulator, and recharge the system with hot water. In the Siggy article the boiler isn't even in the primary circuit so you could bring on the primary circ and run off the heat in the tank, until the boiler is called on to inject some more hot water. I don't know if you would want outdoor reset on the boiler because that would diminish the recovery rate of the water heater. Pretty cool stuff.

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"