Baseboard Element Sizing

dk3100

Baseboard Element Sizing Question:
The application is for a residential home that is heated with a forced-air airtight wood stove. The airtight stove with its ductwork will remain intact, but a boiler hydronic heating system is being installed in order to take the place of heating when need be. I’ve completed a block and room by room Manual-J Heat Loss and sized a boiler to match the heat loss. Copper piping will be laid out in primary/secondary loops. The presumption now is that to get the correct feet of needed baseboard per room, I follow the baseboard manufacturer’s Btuh output rating for the elements (at the boiler output average delta temperature and correct flow rate) to match the Manual-J Btuh loss for each room. I haven’t found a resource on sizing baseboard elements. Would there be any additional baseboard sizing considerations? Thank you in advance.

Jamie Hall

Not really. The baseboard manufacturer gives you the BTUh per foot at various temperatures. You know the temperature you are feeding them with. You know the room heat loss. That's about it.

I hope you are piping them either reverse return or individual source/return to a manifold…

EBEBRATT-Ed

Baseboard is sized at the "average water temp it will see. A conventional boiler is usually sized at 20 degree TD between supply and return. So with a 190 supply and a 170 return you would size the BB at 180 degree. The lower the water temp you run the more fuel you will save but it requires more BB to do the job.

Water flow through the BB should be 1 gpm for each 10,000 btu when using a 20 deg TD

If you are using a mod con boiler you have more flexibility in design. Lower water temps and wider TDs can be used but the design will change completly.

hot_rod

what type if boiler? I would not use primary secondary unless you have a boiler that specifically call for it

Conventional cast iron, copper tube or electric could be direct piped

dk3100

The chosen boiler is a Weil McLain GV90+4, cast iron. It has an exterior mounted secondary condenser. WM had several piping specs to choose from. I chose the primary secondary model because it just fell within their specifications for my application. I did start off with a direct piping model, but the run for the piping was too long according to WM for this Gv90+. Honestly I’m not sure what reverse return or individual source return means?

dk3100

I will learn what reverse return or individual source/return to a manifold means so that I understand those terms but I’m going to continue to pipe it the way that WM specifies, not that your ways aren’t correct or better but because it was laid out pretty clear and if go a different route than the unknown to me will get me. I’m not so sure that the second isn’t what I meant by primary/secondary looping but I’ll clear that up on my end.

dk3100

okay so (page 16-figure 17) from WM shows what I plan to follow, the second (page 17-figure 18) is the direct piping method but my long loop is longer than 103 ft so I wasn’t going to go that route, does this explain better?

Jamie Hall

That diagram doesn't specify whether or not you plan to use serial or parallel piping to the individual baseboards — though it's fine for the connections to the boiler, of course.

In fact, taken as read, it seems to suggest serial piping — all the baseboards in a zone connected with the outlet of one to the inlet of the next and so on. It doesn't mean to, since it doesn't show the zone piping beyond the boiler connections at all.

As I said above, you really must use either reverse return or use individual supply and return lines to each baseboard element — which in turn can all be connected together at a manifold and then to the boiler piping.

dk3100

Jamie, I thank you sincerely for your input as well as your time (as I do for others that contributed). I think I get where you’re goin but was unsure of the necessity of the extra piping of having a supply and return for each baseboard when I had originally thought this out. This is a 1500 sqft single floor home with 40,000 Btuh heat loss. You’re right, the schematic doesn’t really show the pipeline detail past the boiler. The intent was to split the system into two circulator controlled zones with the baseboards within each zone output to input as you alluded to. This was my plan, just as long as the temperature drop is within the “need” of the baseboards heating ability down the line for each room, hence the baseboard sizing question. I’ll heed to your expertise and really relook this.