Looking for advice on sizing 2 pipe baseboard

ldesmarais

Looking for some professional advice with regard to sizing baseboard for my house. It is currently heated with a forced air oil furnace and I want to switch to hydronic baseboard. I am planning on having LP installed at the house for a gas range so I would like to add a condensing boiler to run the baseboard. I have a done a load calc on the house so I have a good idea of what the BTU load for each room is. I want to use Smith's HE2 baseboard with either a parallel supply or top supply bottom return configuration so I can run lower supply temp (140° supply, 120° return ideally). Can I plumb this with a separate loop to each room or should I combine a couple rooms in series? I want to install the baseboard and piping to mechanical room myself while I am doing renovations and I have a contractor install a boiler when I am all done. I'm not getting any luck finding someone that is willing to size the system for me unless they do the whole thing themselves. Any help or advice would be appreciated.

Load Calc.xlsx

Floor Plan.pdf

delcrossv

Hmm. I'd be tempted to do the whole first floor in one series loop. Starting with the bathroom and ending in room 4 bedroom. Generally people want bedrooms cooler and bathrooms warmer. If bedroom 4 faces SE, even better.

psb75

Two zones. 1.) 1st floor and 2.) 2nd floor.

mattmia2

Won't hurt to pipe each room separately but it will use more material and labor. At the boiler you will have to combine them in to a couple zones because you don't want any zone smaller than the minimum output of the boiler. It would let you individually balance the rooms to get the heating even.

Series loop works but to do it well you have to calculate the supply and return temp separately per room one by one on the loop and use the return temp of one room for the supply temp of the next room in the loop to size the emitters in that room.

EBEBRATT-Ed

140 supply and 120 return will give you 10,000 btu/gpm circulated.

I would use a manifold supply and return to each room

Take the heat loss for 1 room and devide it by 10,000 btu this will give you the gpm that room needs. Do this for all room.

Use 130 degree water temp as this is your average water temp (half way between supply and return temp.

Use 1 gpm water flow off their chart

with 130 average water temp the baseboard will give you 356 btu/ft from there chart with top supply and bottom return

Devide the room heat loss by 356 to get the baseboard footage. Repeat for all rooms

Size the manifold supply and return by dividing the btu on that manifold by 10000 to get gpm.

For pipe size to the manifolds (copper)

1//2"=1.5 gpm

3/4= 4gpm

1" =8gpm

1 1/4" 12gpm

ldesmarais

At first I thought the series loop would be good because we prefer colder bedrooms and it would be much easier to pipe it in. It would certainly make it easier to get the temperature drop at the return. The reverse return is definetely more work and a lot more piping but I'm not necessarily looking do this on the cheap. If I were to assume to lowest the boiler can derate is 10k btu than in theory I would need to be able transfer 10k btu to any one of the bedroom loops at one time. While its very unlikely that the other loops would not be calling for heat but I should consider this scenario. The 1st floor bedrooms are 3-4k btu and the bathroom is 1k so I'm wondering if combining those into a loop would be wise. That only gets me to 8k btu on the design day but I cant imagine that the other 1st floor rooms wouldn't be calling for heat. Another thing to consider is I would want to heat the basement to 62-65 degrees in the winter so that zone will likely always be calling for heat. The slab isn't insulated so it gets pretty cold. That would leave me with a zone for the basement (14k btu at 70°), zone for 1st floor bathroom and bedrooms (8k btu), zone for kithen and living room (11.4k btu), and a zone for the upstairs (8.7k btu). Quick calc for the living room (5.6k btu) would warrant 16ft of baseboard at 130° using the top supply bottom return configuration, which shouldn't be a problem. Now I'm not experienced in this area but shouldn't I consider the temperature drop across each emmiter in a loop rather than use the average temperature for all emmiters on a loop? Meaning that the emmiters towards the end of the loop would require more baseboard to get the required btu output since the water temp is now lower. For example, if I consider the living room (5.6k btu) as the first emmiter than I would get an 11.2° drop at 1gpm. Would I then use the 426 btu/hr/ft rating at 140° and 1gpm for the first emmiter? I would then interpolate the btu output for the next emmiter using an inlet temp of 128.8°. Am I overthinking this or is the average temperature drop for the loop sufficent. Thanks for all the feedback on this.

EBEBRATT-Ed

Yes for series loop start at 140 deg and drop the water temp down as you pass through each emitter.

Start at 140 work your way down towards 120..

Manifolds would I think give you more diversity . If you have 3 zones you have 3 places for the water to go. With a manifold you would have as many places for flow as you have emitters. You can use a buffer tank if the boiler does not drop down low enough

mattmia2

I don't know what your heat loss is because there are a lot of steps to opening that excell file but there are many mod cons that are 10:1 turndown ratio and if your heat loss is around 50,000 btu/hr and you can find a mod con that size with a 10:1 turndown ratio your lowest turndown is around 5,000 btu/hr. You can also group zones on the manifold or even use or make a manifold that is just for distribution and balancing and each manifold is controlled with one zone valve or circulator.

you're probably overthinking a little with interpolating but once you set up the formula it is easy enough to do it in a spreadsheet.

EdTheHeaterMan

I find that making a system over complicated never ends up realizing the benefits you were hoping for.  There are things to consider when you have to commission the system, and perform service from time to time.  

1. How do you get the air out of the loops?  
   1. The more loops the more steps you have to do to get the air out.
   2. Piping the double row of ¾” piping piped parallel means that you have to have some sort of valve at each radiator to divert the flow from one pipe to the other pipe in order to purge.   
2. How to pipe the series loop to get the correct size in each room?
   1. If you have each room isolated then each radiator will have a lower temperature as you move down to the last radiator on the loop.
   2. If you have all the tops connected together then loop the last one to the lower pipe and series them all the way back to the beginning, then you will have a consistent temperature in the entire loop.

Then each purge station at the boiler room would be easy to purge using this trick I learned from a Class that Dan Holohan taught and that I included in the classes that I taught.  

In this illustration there are there loops, (that could be 3 zones or just one zone)

1. To purge each loop of air, you just close the full port valve on the common (to all loops) supply pipe.

2. Place a garden hose on the Purge drain valve

3. Close the three isolation valves on the return near the boiler.

4. Lift (or bypass) the fast fill on the feed valve to build up boiler pressure. No need to worry about the boiler relief valve here because the boiler is isolated from the full bypassed potable water pressure.

5. Open the purge drain valve.

6. Open one of the three isolation valves on the return and watch the air purge right thru the boiler (or on a primary secondary system, it may not need to go thru the boiler)

7 Close the return isolation valve and build up pressure then repeat #6 above on another loop, repeat until all zones are purged.  

8. Place the auto feed fast fill back to the auto position (or close the bypass on the fill pipe) and then close the Purge Drain valve.

9. Open the three isolation valves on the return pipe and the full port valve on the supply pipe.

Now you are ready to fire the boiler with no air problems on the water side of the closed system.

hot_rod

There is a Baseboard design module in the HDS software. A trial demo. Select the baseboard, the pump, tube size here.

https://www.hydronicpros.com/product-page/hydronics-design-studio-2-0-free-trial