Feedback on new combo-boiler system design for radiant panel and floor heating

gttra88

Hi there - new to the forum. I bought a home in the mountains of CO last year and quickly found that the existing heating (primarily 2 gas fireplaces on main floor and a handful of electric baseboard) was wholly inadequate. I’m working on remodeling my basement so decided to tackle heating at the same time. I’m in the process of installing a combi-boiler and would love feedback on how I have it set up so far. Please see the attached pic.  

The house is 3 floors and I plan to have radiant panels on the top floor to avoid tearing up the existing floors. I’ll have 3 circuits going to 3 panels for a total of 27k BTUs. The main floor will have 7 circuits of radiant heating in one zone via staple-up for 32k BTUs. The basement will have 2 zones each served by 2 circuits at about 10k BTUs each.   

  

A few questions I have:  

Is the distance from my mixing valve to 3 radiant circulators sufficient or does there need to be a longer straight section before the first tee?

Is the lengthy loop to the first pump okay? I had some space constraints and this layout worked for the area. This is the pump used for the radiant panels

For the radiant floor heating I have the largest pump feeding the largest loop manifold last to not draw too much flow from the smaller zones, is that correct?  

Do I need to run piling directly from the supply to return on the left hand side or is it okay as-is with return coming in through the circuit manifolds (not pictured, will be on opposite wall) to the zone manifold return at the bottom.   

  

My large main floor zone has a vaulted ceiling living room with a much higher heat loss due to the ceilings and a wall of windows and sliding doors. LoopCAD says I need a higher flow rate here of about 1.5 GPMs per circuit. My manifolds have ball valves. Can I use this to control the flow rate? Or should I get a balancing valve? Is it possible to just have the balancing valve on the 2 circuits with higher flow rates? Should I pipe these circuits first into the PEX manifolds to ensure they have a higher flow rate?  

  

For the radiant panel install I have 2 rooms that will have 7,500 BTU panels and a 3rd at 12,000. I plan to have Caleffi thermostatic control heads on each panel. Is this sufficient to control the different flow rate needed for the larger panel? Is there a specific order I should pipe the PEX into my manifold for this zone?  

  

Anything missing from my in-progress install? I still need to add some digital thermostats, control unit, etc.   

thank you jn advance!

EdTheHeaterMan

The first thing that stands out to me as a possible problem is the thermometer installation. Depending on how long the probe in the back of the thermometer is, you may not get accurate temperature readings, Not a game changer but, you might want to shorten up on the extension pipe The illustration on the right is better than the one on the left. The photo looks like the left.

The mixing valve pipe length is fine. Is the pipe size sufficient? Have you considered the total gallons per minute (GPM) the shared pipes are going to carry? To answer that, you may want to read this textbook. It is short and to the point for the NON-Engineer https://www.xylem.com/siteassets/brand/bell-amp-gossett/resources/technical-brochure/fh-z100b-bg-zoning-made-easy-2.pdf. Pages 3 and 4 give you an idea on what pipe sizes you may need to use.

gttra88

Thanks Ed! You are correct on the depth of the thermometers. I thought that having them extend into the pipe could restrict flow, but I’ll adjust. 

I believe my 1” copper main will
be near max capacity at full design load. For the 3 floor zones, I get extra flow from the return through the mixing valve, correct? Let’s say the 1” secondary main has an 8gpm max and 2gpm is being taken by the radiant panel pump. I then have 6gpm leftover flowing towards the hot end end of the mixing valve and then some flow coming from the cold side, so my flow to my floor heating zones could be greater than the 6, correct? In this example my theoretic supply flow rate could be up to 10. Am I thinking about this correctly or am I way off base? 

gttra88

Also - question. on check valves I currently have them installed on the output side of each pump. Are these needed since I have a mixing valve? I also have a check valve on the return water input side of the mixing valve. Is that the correct place or should I put it before the radiator return? 

hot_rod

The circuits that need 1.5 gpm, what size tube, how long is the loop.
Where is the fill valve tied in, ideally it wants to be at the expansion tank
Interesting bulge fitting for the P/S
Really no need for the check on the mix valve, pretty high flow resistance in those valve
Is that a y strainer down low, be sure to check it after fill and flush, they can add a lot of pressure drop, with not much debris in them

gttra88

The 1.5GPM circuits are 250’ each of 1/2” PEX.

I have a fill valve and backflow preventer in the bottom right going into the auto-fill line of the boiler which is how they showed it in their diagrams.  

  

Yeah, I bought the P/S already assembled like that from the manufacturer and had to size down. In retrospect I would have done it myself and saved a couple hundred bucks.   

Yep, that’s a y strainer. I plan to flush it for a while when I fill it, empty strainer and repeat one more time. 

hot_rod

gttra88 said:

The 1.5GPM circuits are 250’ each of 1/2” PEX.

I have a fill valve and backflow preventer in the bottom right going into the auto-fill line of the boiler which is how they showed it in their diagrams.  

  

Yeah, I bought the P/S already assembled like that from the manufacturer and had to size down. In retrospect I would have done it myself and saved a couple hundred bucks.   

Yep, that’s a y strainer. I plan to flush it for a while when I fill it, empty strainer and repeat one more time. 

Does LoopCAD give you the circ spec for the various zones? How many loops in that great room zone? Or total gpm.

That great room, 1.5 gpm is a bit high for a 1/2" loop, about 16' head, probably out of reach for a small Alpha

.7 gpm would be about 4' head, as a comparison.

gttra88

LoopCAD says about 7.3GPM across the 7 circuits in the main floor zone. I did size that zone with a bigger pump - a Alpha1 26-99 with 42ft of head vs 15-55s with 19ft in the other zones

hot_rod

7 loops at 1.5 gpm would be 10.5 gpm?

7.3 is more reasonable, a 1 gpm requirement. What is the heatload number for the great room. Btu/sq.Ft.

About a 90,000 total load? Your 1” piping should be adequate.. A circ inside the boiler I assume?

gttra88

Yep, total across the 7 circuits is 7.3, but LoopCAD is recommending a higher flow rate in the great room due to the heat loss which is why I’m wondering if I can or should get balancing valves just for those 2 circuits. I’m estimating about 45btu/ft heat loss. Even with the floor heating LoopCAD is saying I’ll need supplemental, which I have with a gas fireplace. One of the main reasons I’m adding this system is because current heating is inadequate. I struggle to keep the main floor above 60 degrees when it’s near the design temp.   

Yes, the boiler has an internal circulator and total load looks like around 85k. Thanks for all the info and help!

hot_rod

25- 28 btu/sq ft is the high side output for a radiant floor, without excessive surface temperature. Perhaps adding the floor output to the output from the fireplace you will get there.

You mentioned current heating system, is that the gas fireplace?

It always comes down to the surface temperature when you determine floor output.

The math works like this, 2 btu/ sq. Ft for every degree difference

So with a room at 70 and floor at 82, 12x2= 24 btu per sq ft

The options to increase output is hotter floor, uncomfortable above 82, or run a lower ambient

82 floor temperature- 68 ambient= 14x2 28 btu/ sq ft

If in fact design day load is. 45, you are a long ways off. The programs always show this shortfall, and required supplemental.


Typically 80% of the heating season you will make it, the closer to design day, the more it slips out of reach. But you already know that condition.

I supposed you covered all the options to lower that great room load?

Yes to the question to balancing the low load room loops at the manifold.

gttra88

Yep, current heating system is a couple fireplaces on opposite sides of a wall in the middle of the main floor. I believe there used to be a lot of electric baseboard heat but most of it got eliminated over the years. The great room has vaulted ceilings that go up to 20’ with about 180 sq ft of glass which is why the heat loss is so high. Eventually I’ll likely get foam injected into the walls, so that will help some too, but ultimately glass just has a lot of heat loss. It’s worth it for awesome views of the Rockies, just trying to make it a bit more comfortable. I’m definitely open to a lower ambient temp on design day 65 or 66 is still pretty comfortable compared to -10 outside

Mad Dog_2

Very neat and sqaured away piping job. Mad Dog