New to system design, all of my questions in one post.

NCB

Hi All,

I am a custom home builder and I got convinced by a customer/friend of mine to do a radiant heating setup for him. I am totally new to this having no prior experience with radiant heating and I'm just trying not to mess this up. I am going to post some details of my plans and ask if you all would mind giving it a critical look to see if I've made any substantial errors. Then, I'll follow up with the questions that I may have. I would very much appreciate it if you all would lend any knowledge that you may have. Thank you!

The plan:

I've installed 8 loops of 5/8 pex into the basement floor slab of his home. It's a walkout basement with a polished concrete floor near Pittsburgh, PA. Most of the loops are around 350' +/- about 25'. I have one short loop at about 150', but that loop runs through a wine cellar and may not be used at all. I also put a loop in his front porch for snow melt that I may try to run through a heat exchanger later but I am not concerned with that at this time.

I plan on using a primary-secondary setup with a noritz combi boiler and zone valves. I designed the system for a delta T of 15 degrees and a 100 degree water temperature. I used a trial period of LoopCAD to do the design, and it is showing a heat load of approximately 24,000 BTU. I'm attaching a schematic layout and some reports with this post.

I have to say that I just don't trust LoopCAD for some reason and I feel like I'm doing something wrong, so I'd like some confirmation that everything looks good or not good. Also, the part that has me a little lost is sizing the circulator pump. All of the calculations from LoopCAD show very low flows through my loops (<0.5 gpm), so the head loss calcs seem to be based on that amount of flow. It also doesn't seem to be accounting properly for the height of my manifold from the floor (6ft). The total flow and head loss that the program calculates is 2.95 gpm with 2.2ft of head loss.

Based upon my poor understanding, it looks like even a 1/25hp pump will easily handle this, and will likely pump way more gpm through my system. Is this going to be a problem?

Thanks for your insight. Also, I'm going to add a list of my planned components below. Excluding valves and such, is there any major component that I may be missing?

1x Noritz NRCB199

2x Honeywell HPZC104 4-Zone Controller
9x Honeywell V8043F1036 Zone Valve
1x Taco 1" Premium Near Boiler Trim Kit
1x Taco 0013 Pump

Hot_water_fan

All of the calculations from LoopCAD show very low flows through my loops (<0.5 gpm), so the head loss calcs seem to be based on that amount of flow. It also doesn't seem to be accounting properly for the height of my manifold from the floor (6ft). The total flow and head loss that the program calculates is 2.95 gpm with 2.2ft of head loss.

The flow needs are really low here, so the head loss is correct. The 6ft is irrelevant since it’s a closed system. If you pump more flow than design, your delta T will shrink. No big deal. 

I would rethink combi feeding into a tank. You would be better off using a heating only boiler + an indirect or just separate DHW entirely. You use a combi when you are short on space, which you’re not here, so it’s pretty pointless. A benefit of a heating only boiler is that it can be smaller - the NCB only turns down to 18kbtu while a typical 80kbtu modcon can turn down to 8kbtu. If you go the indirect route, the DHW gets its own loop and is at a higher temp then the floor loops. 

Why is there space for a second future boiler?

Congrats on giving this a try! 

GGross

Since this looks like a basement, and it kind of looks like there is a big opening wall down there. Did you make sure to input that large opening wall? any wall that is not underground I like to section off with input points (right click the wall area, select "insert point" and then set the point where the sections that are not underground start and finish) then you must manually select these "above grade" sections of wall by right clicking, and selecting wall properties, then adjust the depth below grade of that wall section to the correct value. depending on how many walls in the basement are "above grade" and how many doors/windows you may need to add, this can drastically change the load of a basement. You also need to mind the construction type for any door that is not solid, if you know the exact R value of the door that goes a long way to getting really accurate.

I would say if you made sure to set any window walls with the correct size windows, and the correct depth below grade and do the same for any doors then I would trust loopcad, I use it every day

dko

Hot_water_fan said:

I would rethink combi feeding into a tank.

He's doing the reverse, feeding the combi with preheated water. If you were to put a tank.. would put it as a storage tank on the supply for the cold water sandwich. But agree an indirect or separate DHW system would do you better. Or even a dhw recirculation system over your current plan.

What's your DHW load?

KC_Jones

Hot_water_fan said:

I would rethink combi feeding into a tank. You would be better off using a heating only boiler + an indirect or just separate DHW entirely. You use a combi when you are short on space, which you’re not here, so it’s pretty pointless. A benefit of a heating only boiler is that it can be smaller - the NCB only turns down to 18kbtu while a typical 80kbtu modcon can turn down to 8kbtu. If you go the indirect route, the DHW gets its own loop and is at a higher temp then the floor loops. 

Why is there space for a second future boiler?

Congrats on giving this a try! 

This.

Your load is 24k BTU according to what you posted. The combi you are proposing would be like using a tractor trailer to commute to a desk job, yes it will work, but it's not the best choice for the application.

You need the smallest boiler made and even that is oversized. As stated the Modulating Condensing boilers have a turn down. For me, you are sizing for the bottom end, not the top end. So you want the turn down as low as possible. Remember that 24k is when it is 6.1° outside, the rest of the time it's lower.

With outdoor reset the goal is to get the radiant to flow continuously, or as close to continuously as possible. This maximizes comfort and efficiency, that is, if you install a more logical boiler size.

Hot_water_fan

@dko you’re right! Even worse. 

GGross

For this setup with a boiler that is far too big, and a tank, I would also recommend just using a boiler mate and eliminate the combi aspect, but to each their own I suppose

NCB

Thank you all so much for the input. I really appreciate it. To address some of your concerns and continue the conversation:

I did make sure to set all of the correct grades and r-values on the walls, and there definitely is a giant 18x8 opening in the back wall that you can’t see. But it is there and with a correct r value assigned, so I think I’m good in that area. Do you guys think you might be able to make some recommendations on the correct pump to use?

The original plan was to use a small electric water heater for a storage tank. After talking to my noritz, this is the configuration that they suggested. My client liked this configuration because we would be using electricity for the bulk of his water heating, because he’s concerned with limiting his propane use but we would still have unlimited hot water and I believe eliminate the cold water sandwich. Though I’m still open to other options. I do plan to recirculate, I just didn’t add that to my drawing. 

I didn’t consider the fact that the boiler is very oversized, I was looking mostly at the DHW flow capacity. Maybe I will think about using an indirect for the storage tank, though that would eliminate my propane redundancy. That’s what the future boiler was show for, possible redundancy. 

One think I didn’t do was embed slab sensors anywhere, and the floor is polished concrete so I can’t really put any in now. I could probably get something in under a wall plate, but I purposely kept the piping away from the walls and I would kind of be measuring between two different loops in most areas. Do you think I can get by with just air temps? I am very concerned with overheating. Thanks again!

NCB

I will add that whatever I do definitely needs to be wall mount. Space is very much an issue as I am trying to cram all of this into about a 5x5 space. 

GGross

There are many radiant jobs that don't have floor sensors installed. It is generally agreed upon to be a good idea though. With a proper heating curve setup you should be OK there. I do think it is strange they want a small tank with a combi, and also a redundant boiler and are only giving you a 5x5 space, it makes sense that the owner wants to use 2 fuel sources to some extent, that is more of a personal choice to be made. For me I would either use a separate tank water heater, or a boiler and boiler mate. Seems like you are rarely going to run the combi, but will still get the same amount of scaling and build up as the hot water will always have to run through it, also another potential failure point. These concerns I think are best weighed with the owner though and there are some potential benefits of redundancy as you pointed out.

Hot_water_fan

The original plan was to use a small electric water heater for a storage tank. After talking to my noritz, this is the configuration that they suggested. My client liked this configuration because we would be using electricity for the bulk of his water heating, because he’s concerned with limiting his propane use but we would still have unlimited hot water and I believe eliminate the cold water sandwich. Though I’m still open to other options. I do plan to recirculate, I just didn’t add that to my drawing.

This makes more sense! You could also just size up the electric tank. The "unlimited" hot water is just marketing BS. The fine print is "Unlimited hot water if you never exceed the flow rate". So assuming you have a delta T of 80F, this combi can do unlimited hot water of (200,000 * .95 / (80F * 8.34*60)) = 4.75GPM. That can handle 2-3 typical simultaneous showers with no issue!

But if you have 1 2GPM shower and are doing a load of laundry simultaneously, you're screwed: one hot draw from the washer can easily be 5GPM of hot water, so your 1 shower immediately goes cold. This is why a tank is superior, they have better performance for equivalent efficiency.

I didn’t consider the fact that the boiler is very oversized, I was looking mostly at the DHW flow capacity. Maybe I will think about using an indirect for the storage tank, though that would eliminate my propane redundancy. That’s what the future boiler was show for, possible redundancy.

What do you mean by this? An indirect could be heated by both propane and electricity,

hot_rod

As you can see, identifying the DHW load is just as important as the heating load with combi and tankless. Unless the homeowner has an idea of how much DHW they currently live with, it is a bit of a guess.

I suspect many owners that have tankless or combi learn to live within their capacity, stager large lods for example.

The same applies to an indirect. I've had customers completely drain an 80 gall0on indirect to fill a large soaking tub. So then you still need a large boiler to recover that load quickly. Much larger than your heating load in this case. Same math applies 500 . Flow (delta T)
Typically a 70- 77 delta T, so plug in your desired flow.

To bad about the space constraints, a HPWH could be another way to use off peak electric rates and have a large 80 gallon buffer to the tankless or indirect.

Indirects are still available with electric element back up, solar tanks, but typically a single 4500W element.

NCB

Thanks to everyone for your feedback. Do you all have any opinions on what type of pump I should use? Is there any reason I should use anything more than a 1/25hp?

GGross

NCB said:

Thanks to everyone for your feedback. Do you all have any opinions on what type of pump I should use? Is there any reason I should use anything more than a 1/25hp?

If you haven't already done so, you can also add the supply and return piping lengths/sizes/material to the manifold using loopcad. If you have that information entered I like to go to the reports section and look at the "water supply summary" this will give you exact pumping requirements for each manifold using the information you entered. You can also add in additional head loss of fittings if you plan to have fittings in the supply/return piping that will add additional pressure drop to get it really precise, I also like to make sure I have the correct manifold selected as different manifolds will have a different pressure drop. If you have already done all of this then you are golden. More than likely though, you will be using the same size pump, I just like to make sure I take the extra few minutes to input everything as close as I can

Dave H_2

The 0013 circulator is certainly too big for the application, the 0015e3 is a much better choice, set on Low.

Use a radiant manifold with actuators, instead of building a header with zone valves if thats what the drawing indicates. Actuators are zone power heads.
Setting the 0015e3 on low will make it a variable speed circ, speeding up and down as actuators open and close.