Manifold Question

jb9

Hello,

I am new to Radiant Floor heating, but I am trying to increase my understanding. I am installing a system in a new house and have some questions about manifolds. The house will be 4 zones, 2 floors and 1500 sq. ft. Do I need two manifolds (one for each floor)? What is the best location for a manifold? If I don't think I will add on to the house, should I just purchase a 4 loop manifold? What is the optimal way to mount a manifold? Which is superior in quality (SS or brass)?

That's a good start for now. I will start compiling a list of materials and follow up when folks make recommendations. I want to thank the many knowledgeable folks here in advance.

Thanks.

Rich_49

a 4 loop manifold in a 1500 sq ft home is not advisable in most cases . Maybe if it is a super insulated home it could do but not any I've seen . How did you come up with this plan and the zoning strategy ?
Was a heat loss done room by room ? Who , if anyone assisted you in determining loop lengths , spacing , flow rates supply water temps and head loss ? We will be more than glad to help you but need more information . What boiler will you use for this system ? How will domestic hot water be produced . Do you intend to put southern facing rooms with plenty of glass on the same zone with rooms that do not share solar heat gain characteristics ? Many things must be thought of to design and install a properly operating radiant system that will meet your goals and expectations .

Everyone is an expert until start up and the weeks that follow .

jb9

Hi Rich,

Thanks for the response. Those are all great questions. The house is a 24x32 timber frame and it will be enclosed with SIPS (wall-6 1/2" at R-23 and roof-12 1/4" at R-45). I have an open floor plan on the first floor and 3 bedrooms and 2 baths on the 2nd floor. I thought I might shoot for optimizing and build it as a passive solar structure, but it's in a location in the mountains that is too cold to successfully implement such a design. The house will be sited such that the broad side (32') will be facing true south and I will try and run a reasonable amount of glazing. I am using the Chelsea Green Passive Solar book to do my heat loss calculation on the total structure. 2 of the 3 bedrooms will have south windows. The 3rd will be on the northwest corner of the house. Since the house is a simple rectangle, I figured I could design a 2 loop per floor, 4 loop system using WB. The supplier is going to provide a materials list, but I need to do my due diligence before I move forward. I was thinking of using a dark tile floor (with a high heat absorptivity factory) near the south facing windows to capture some of the solar gain but as I mentioned, I won't be approaching the design as a pure passive solar solution (especially since I will have a basement instead of a block slab to allow the capture and air flow as is required by those homes). I have not sized the boiler yet as I need to finish my heat loss calculation for the structure. I am going to do it manually but if you can recommend a good online calculator, that would be great. I read the Chelsea Green book and have a handle on the calculations but I probably won't approach them with the same level of precision (yet). I will have domestic hot water yes. The house will not have natural gas. Only electric.

I hope that is a good first pass at answering your questions.

Thanks.

jb9

It looks like I neglected to answer a couple additional questions. The system uses 1/2" pex-al-pex on 12" centers. I am trying to keep my loop lengths around 270'.

Rich_49

Are you thinking of Warmboard S or R ? Warmboard is a fine product and is the best 12" on center product available , that being said , the tighter the tube spacing the lower the water temps required . There are no other structural products to my knowledge but if the structural part of this is not what you are most concerned with you may want to look at Sunboard graphite coated 3/4 board x 1/2 tubing . Much better price point lower water temp ability and less stuff to heat up prior to emitting to the room .
What CZ are you in and what do you predict ACH natural to be ? Although those passive gain days may be few and far between , they cannot be ignored and should be zoned for . I would not let anyone scare you into overheating either since the water temps you will quite probably be running will be lower than or right around those solar surface temps . Too many geniuses out there that did these early on with bad results that just cannot admit they did it wrong , I assure you , they did it wrong .
Have you thought or even heard of radiant ceilings ? Even less resistance in drywall and less concern about surface temps . A good option unless your ceilings are not drywalled as I have seen that detail also , PITA !

The right electric water heater can possibly heat the house with proper design and isolation . Take a look at Nyle Geyser heat pump also . Easily connects to water heater , plugs into a 110 outlet and provides 6,750 BTUh and can get you up around 130* . You may never have to have the elements come into play in the summer and in the winter it will be a big help . COP is right around 2 but at the price point it is a great little unit .

jb9

Good suggestions Rich. I am in Zone 6 (bordering on Zone 7) and I am compiling the monthly HDD Data now from degreedays.net. My house design will have floor joists that are exposed below (simple rustic aesthetic and structure) so that has informed my decision to go with the WB. Your point about the tighter loop is a good one. When you say don't let anyone scare me about overheating, do you mean that I should be conservative and run the WB-S even in the floors that will capture some sun? I just want to make sure I understand. Let me keep crunching numbers and get that ACH (heat loss by infiltration, right?) for you.

Thanks Rich.

Rich_49

ACh , air changes /hour .correct .

jb9

Ok. Here are some numbers I ran. Please let me know if I am on the right track.

Volume of house (basic geometrical calcs hopefully I can do):
16402.24 sq.ft.

Air Changes per hour recommended are 2/3 which is .66666667

Wall Area is 2131 sq.ft. at R-23

Roof Area is 952.3333 sq.ft at R-45

I have in my design notes that I am on the border of Zone 6 and Zone 7.

Here is a list of 65 degree HDDs on a monthly basis:

Month starting HDD
10/1/2012 726
11/1/2012 902
12/1/2012 1292
1/1/2013 1587
2/1/2013 1218
3/1/2013 1108
4/1/2013 837
5/1/2013 509
6/1/2013 286
7/1/2013 134
8/1/2013 125
9/1/2013 346
10/1/2013 848
11/1/2013 1016
12/1/2013 1511
1/1/2014 1409
2/1/2014 1096
3/1/2014 996
4/1/2014 775
5/1/2014 434
6/1/2014 334
7/1/2014 129
8/1/2014 239
9/1/2014 334
10/1/2014 592
11/1/2014 1131
12/1/2014 1179
1/1/2015 1338
2/1/2015 938
3/1/2015 836
4/1/2015 731
5/1/2015 522
6/1/2015 201
7/1/2015 199
8/1/2015 188
9/1/2015 285

I will continue my calcs in the book, but I wanted to share what I have so far...

rick in Alaska

I would be highly surprised if you needed half of that much need in a sips house. But, you question is on manifolds.
You will want a manifold per floor. Placement is a matter of juggling where it can physically go, how you will be able to get your loops out of it without crossing each other, and what it takes to get the line from the boiler room to it.
The number of loops per manifold will depend on your heat loss plan with how many loops per zone. Most likely looking at a 3-4 loop manifold.
You can get manifolds in all kinds of materials including plastic. They all seem to work just fine and hold up ok from my limited experience. Stick with something that has been out there awhile to make sure there are parts available in the future if needed. We have hundreds of the old style brass Wirsbo manifolds around here that are starting to leak out the cartridge assembly, and they discontinued it. No parts available. Now we have to go in and change out the whole manifold if we have one leak. Very expensive.
Hope this helps.
Rick

jb9

Thanks for your thoughts Rick. I thought 4 loops would be fine but I will keep digging. Should I get a manifold per floor with an extra loop or just get a manifold that matches the number per floor? I have seen a Watts SS but I don't know all the reputable brands/models so feel free to throw out suggestions.

SWEI

With those kind of R-values, you might want to try something like a 50°F base temp for your HDD.

jb9

Thanks SWEI. I am confused. What is the reasoning behind changing the base temp value? I'll admit I am new to all the parameters/values of a comprehensive heat loss calculation and analysis.

SWEI

The base temp (or balance point) is the outdoor temp at which you need to start heating the building. You don't actually need it or the degree-days for a heat loss calc, since that is done at worst case (outdoor design temp) conditions. Those come into play when you want to estimate fuel use, ROI, etc.

jb9

Ok. I think I get it. The idea is that based on the chosen design elements (a tight envelope with high R-Value SIPS), I might not need to start heating the building until the outdoor temp hits 50 degrees, right? Additionally, I always do heat loss calculation for the worst case (coldest day of the year) scenario, right?

Thanks for the follow up. I am starting to understand it. The calculations are basic, but comprehensive... I think if I can get through it once, it will make sense.

I just spoke with a SIP manufacturer and he said that roughly SIPS get between 1/.5 of ACH50 and then I (roughly) divide that by 7 to get the ACH natural. If I used .75 / 7 , I will get an ACH natural of .1071429. From that I guess I apply that to the total cu. ft. of my structure (16,402.24) and get 1757.38 cu. ft. of air that needs to be replaced and heated, right?

jb9

One additional question. Should I include the attic space in my total volume? I included it and I think that might be incorrect.

Rich_49

Is the attic inside the thermal envelope or is it ventilated attic ? How bout the basement ?

Your manifolds may very well be on the second floor and run down from t here . Rick is possibly correct but those statements cannot be made until you have heat loss numbers and we can see a floorplan . Is that possible , at least the floorplan part ?

With an ACH number like that you will require mechanical ven tilation. Balanced is the only type that will do , You'll want to look at HRV and ERVs for this . Your heat loss is gonna be very low , house identical in construction but not size came in at 11.4 BTU sq ft . That ACH number was a 2.1 NAT but the home is 13,000 + sq ft with a couple very high ceilings @ 25 feet tall . You very well may have a design load of less 20000 BTUh .

Rich_49

Since you are doing radiant you'll want to not s pend too much time performing block loads such as total volume and the like and concentrate on room by room . If you have large areas that adjoin to the North and South sides you c an enter them as one large room but entering them as 2 would be ideal .

jb9

Hi Rich,

I am attaching a jpg of the model I am building. From the view shown, you can see the floor plan/bedrooms of the 2nd floor and the open floor plan of the 1st floor with the area that will be exposed to the south/sun as you look at the jpg. The timbers are all structural of course so you can get a feel for my design constraints as I am managing the way the system will be laid out (which is essentially the original question I was asking about manifold placement). The central bay on the 2nd floor will be a pair of closets for each bedroom (sound insulation) and a good central location (in my opinion) for the manifold. Hopefully this helps. The roof will be 12" SIPs so I am still trying to determine if it will be in the thermal envelope. I probably won't turn it into useable space.

jb9