Radiant flooring - fundamental misunderstanding of zoning

SteamtoHotWater

I’m contemplating the installation of radiant flooring in between joists for both my first and second floor. Trying to figure out what I can DIY (loop runs, simple plumbing) vs hiring a pro (new boiler install).

Simplistically, my house is 1930s, stone, original wood windows, minimal insulation, mostly square in shape, 700 sq feet on the first and 700 sq feet on the second. The first floor has the living room in the front of the house and the kitchen and dining in the back. The upstairs is three bed and one bath. The house is in the upper midwest and heat loss has been calculated at 54K 45K BTUs.

In drawing loops, there are essentially four quadrants on each floor - each with loops of ≈ 225 feet. So, there are eight total loops.

I would like Four zones.
1) Living room in the front of the house that gets significantly more sun.
2) Kitchen and dining in the back
3) Master bedroom upstairs
4) Two bedrooms and bath upstairs

I think I’ve decided on one circulator pump and an eight port manifold. Zoning would be controlled with zoning valves. But, here’s what I don’t get - how many zoning valves do I need? Surely, the answer isn’t eight. But in researching it looks like ZVs are always attached directly to the manifold. Can one zoning valve somehow control two loops or three loops?

Separate, but related questions:
Is there a benefit to having two circulator pumps and two four port manifolds, one for upstairs and one for down, instead of one eight port and one pump?

The reason for the needing two zones upstairs is the master bedroom needs to be kept cold. Currently, the heat is kept off in this room. Does that really require a zone? Or, can I simply shut off, or greatly reduce, circulation to the room?

Jamie Hall

If you have four zones, you need four zone valves. The valves control the flow from the header to the various zones; you can have as many loops as you like running from a manifold for each zone.

You will also need to pipethis thing primary//secondary -- which may need another pump unless the boiler already has one. You will also need to be able to balance the flow, and control the temperature of the flow in each zone.

Radiant floor heat isn't on and off. It's always on, and the circulating water temperature for each zone is adjusted to maintain the temperature in that zone.

Not quite as simple as I think you are hoping...

Hot_water_fan

54kbtu is a HUGE heat loss for that square footage and you’ll probably not be able to heat the house with solely radiant floors if it’s accurate, so let’s take a step back. Can you show your heat loss calculations? Was it double checked against reality (ie fuel usage)? The software heat loss calcs are usually worse than useless. Having a bloated heat loss will mean you’ll need more flow which means more pumping power and/or larger tubing, if the floor can even output enough heat without burning toes. It’s worth getting that right or abandoning the project altogether if it’s not feasible before any $ are spent. 

SteamtoHotWater

If you have four zones, you need four zone valves. The valves control the flow from the header to the various zones; you can have as many loops as you like running from a manifold for each zone.

So this is my fundamental understanding - in my case, eight loops running to eight ports, where do the four zone valves go?


Using this photo, how does the ZV possibly control anything other than the loop it's directly attached to?

Was it double checked against reality (ie fuel usage)?

The number was given to me by a contractor bid. Sadly, I think it's only off by about ≈20%. According to my energy company, I use nearly twice the natural gas as similar homes. In the dead of winter I use 9 therms per day.

Hot_water_fan

The number was given to me by a contractor bid. Sadly, I think it's only off by about ≈20%. According to my energy company, I use nearly twice the natural gas as similar homes. In the dead of winter I use 9 therms per day.

So you don’t have a heat loss, sadly. You’ll need a competent one! 9 therms per day (a lot) is still only 30kbtu average per hour if you don’t use gas for anything else. That’s “only” 80% off, don’t let that contractor anywhere near this. 

This is important because 1400 sqft can only emit so much heat - in reality it’ll be much less than 1400 sqft due to staircases, cabinets and the like. Right now, this might not be feasible. But! There’s good news if the heat loss is substantially less. 

 The manifold is the easy part. 

SteamtoHotWater

That’s “only” 80% off, don’t let that contractor anywhere near this.

Relooking at his emails, I misrepresented his numbers and intent. According to him, I'm using 37,000 BTUs, at most. His heat loss calculation is 45K BTU, and is padded +20%. He's getting to get back to me with a quote for a boiler install of around 54K BTUs.

He's the first contractor I've met with. I like him because he's willing to quote just the boiler install and give me some guidance on the rest.

The manifold is the easy part.

Good, because it's one of the things I'm attempting. Don't suppose you have any insight to my original manifold question? How does one zone valve control multiple loops?

Jamie Hall

"Good, because it's one of the things I'm attempting. Don't suppose you have any insight to my original manifold question? How does one zone valve control multiple loops?"

You actually have to have a total of six manifolds, not one, plus a low loss header. Assuming that you can balance the system with only one circulating water temperature.

You start from the boiler with the primary circulating pump. This pump feeds a "low loss header" which returns to the boiler, but has two takeoffs. One goes to the secondary circulating pump, and the other gets the return from the heating system. In between the takeoff from the low loss header and the secondary pump there is a mixing valve. The hot side is connected to the header; the cold inlet is connected to a bypass from the system return. The mixed side goes to the secondary pump.

The secondary pump feeds a manifold with one inlet and four outlets. Each outlet is controlled by a zone valve. The outlet from each zone valve splits into two branches each of which feeds one loop (these should be controlled by balancing valve, to ensure that each loop gets equal flow. The returns from each loop join together through check valves and can all go into one eight plus one manifold. The outlet from that manifold goes back to the primary loop, with a takeoff to the mixing valve as noted above.

The secondary circulating pump is always on, and assuming that you get the system properly balanced to your liking, the zone valves are always open.

The mixing valve should be controlled by outdoor reset.

The boiler runs as required to maintain enough heat in the hot feed to meet the desired mixing temperature output.

Now -- can a radiant system do the job? Maybe. As has been said, there is an upper limit to what a radiant floor system can do. Being somewhat generous in the amount oof actual radiating floor space -- and with actual heat output of the floor -- you have enough area to provide about 26,000 BTUh heat. I don't share @Hot_water_fan 's dislike of heat loss calculations -- if they are done right, they are actually quite reliable -- and if we assume your contractor's calculation is anything like correct...

You don't have enough floor area to meet your heating load. In fact, you are not even close.

This is a problem...

SteamtoHotWater

You actually have to have a total of six manifolds, not one, plus a low loss header. Assuming that you can balance the system with only one circulating water temperature…

I'm going to slowly read everything your wrote and see if I can make sense of it. Expect more questions ; )

You don't have enough floor area to meet your heating load. In fact, you are not even close.

It's certainly possible, I'm wrong. All of my info is from people trying to sell me stuff.
I did not earlier mention that, within each joist, I'm planning on using extruded aluminum heat transfer plates with fiberglass R19.
I was told that, given an appropriately sized boiler, with 130º AWT, I can expect a minimum of 25 BTUs per square foot of insulated joist. That should be about 600 sq feet per floor, or about 15,000 BTUs per floor. Am I just misinformed?

GGross

You can expect a maximum of 25 BTU/sqft of radiant floor. Any higher than that and the floor itself will most likely be over temperature which can result in several undesirable effects

hot_rod

The wood build up of the floor can also put the brakes on the btu output. So you need to look at the design part carefully

Panel radiators can add attractive “radiant” supplement.

GroundUp

Yeah, you'll never achieve 54k with underfloor and especially not with only 900LF of tubing per level. What is heating the home currently? Maybe the floor can just be supplemental? To answer your zoning question, yes you can use one circ and one manifold set. In order to zone as you describe, every loop would require a zoning actuator and whichever loops make up a zone would be wired together so they operate together. Only the appropriate valves would open with the thermostat call, while the rest remain closed. Personally I would probably run one manifold set per level and still use actuators on them, which can still be done with one circ if piped properly.

Hot_water_fan

Relooking at his emails, I misrepresented his numbers and intent. According to him, I'm using 37,000 BTUs, at most. His heat loss calculation is 45K BTU, and is padded +20%. He's getting to get back to me with a quote for a boiler install of around 54K BTUs

That’s much better! Boilers don’t come in many sizes - it’s like shopping in a shoe store where every size is a multiple of 5. 54k is about the smallest boiler that’ll work for you. The overall heat loss should be in the ballpark for the floors. 

SteamtoHotWater

You can expect a maximum of 25 BTU/sqft of radiant floor.

Got it. Thanks. I'll definitely reevaluate.

In order to zone as you describe, every loop would require a zoning actuator and whichever loops make up a zone would be wired together so they operate together.

That's what I was missing - that multiple actuators can be wired to operate together. Thank you.

Personally I would probably run one manifold set per level and still use actuators on them, which can still be done with one circ if piped properly.

What's the benefit of one manifold per level? Could you also elaborate on how proper piping allows one circulator to operate two manifolds?

Lastly, if my intent is just to keep one bedroom much colder than the others, do I really need a zone, per se? Could I just switch off that loop without any ruining the flow/balance to the rest of the upstairs?

Solid_Fuel_Man

This can be one 8 loop manifold. I wouldn't ever try to put 4 zones on each floor. Maybe each floor is 1 zone in a 700 square foot house. 

Zones should just be grouped by temp. So, bedrooms are a lower temp than say the first floor. 

Although the 1st floor likely will do most of the work heating the house. 

None of this is to say underfloor radiant will work. I'll let the others do the math!

SteamtoHotWater

I wouldn't ever try to put 4 zones on each floor.

Right. That's not the intent. Each floor will have four loops.
First floor - two zones, the front of the house gets a lot of sun, the back gets nearly nothing.
Second floor - two zones? Again, ideally this would just be one zone with the master bedroom shutoff. I just don't know that this is feasible.

Hot_water_fan

Lastly, if my intent is just to keep one bedroom much colder than the others, do I really need a zone, per se? Could I just switch off that loop without any ruining the flow/balance to the rest of the upstairs?

I’d just zone it and keep the temp low. Easier than fiddling with it every time the outdoor temp changes 

hot_rod

Too much zoning leads to what we call "micro loads" and this can cause the boiler to short cycle if just a small bath zone was running. There are some options if you must have a small single loop zone, like adding a buffer tank to the boiler or use a tank type heater/ boiler. HTP for example.

But the load calc and design needs a closer look to see what is doable.

Radiant walls or ceilings may be an option? You get more btu/ sq ft as you can run a higher surface temperature.

A few helpful pics and formulas.

Notice the big difference between bare tube and aluminum plates. This is true for floors, walls and ceilings.

Also the math to determine output difference between walls ceilings and floors.

Walls come in with the highest output. ceilings get a small amount of stratification which limits output a bit.

Download this Idronics issue if you want to learn more about heat transfer in general.

EdTheHeaterMan

SteamtoHotWater said:

Relooking at his emails, I misrepresented his numbers and intent. According to him, I'm using 37,000 BTUs, at most. His heat loss calculation is 45K BTU, and is padded +20%. He's getting to get back to me with a quote for a boiler install of around 54K BTUs

;

Boiler ratings can be somewhat confusing. With boilers there are 3 different BTU Ratings that need to be observed. It all has to do with how efficiently the heat from the flame gets to the room. To go back to the beginning when these numbers were conceived over 100 years ago, it looks something like this.

Let's say that a particular boiler has a 100,000 BTUh burner. That would be considered the Input, and that is the number you need to use to size the gas pipe. If the pipe is too small then you may not get 100,000 BTU of gas to the burner. That number has little to do with the Heat Loss of the building.

The second number is the output of the boiler. Let's say that the boiler design was able to absorb 70% of the heat from the flame, and 30% of the heat went up the chimney with all the combustion gasses that you don't want to breath. By today's standards that boiler would be pretty inefficient, but 100 years ago that might have been one of the most efficient boilers on the market. If we were to compare that boiler to the rating of boilers today we might say that the boiler was 70% efficient or might have a 70,000 gross output. Today we call that DOE output.

The third number is the NET output. That is an arbitrary number that was given to boiler ratings by the Institute for Boiler Ratings a long time ago. You may see it on the rating plate as I=B=R Net. That number for hot water boilers is about 15% lower than the actual output of the boiler. It is an allowance for what is known as "piping and pickup". In other words the NET is allowing for an additional heat loss that the pipes might lose between the boiler and the radiator(s). So you might see a 100,000 BTUh input with a I=B=R Net rating of 59,500 BTUh. Today that I=B=R NET rating is called DOE NET or just NET

Today's more efficient boilers have more efficient numbers affixed to the rating plate. The Red outlined number of 140,000 BTUh is the input, The Blue outlined number of 115,000 is the gross output which makes this heater about 82% efficient. The White outlined number of 100,000 is the NET BTUh output used to match the load calculation for the building. And that is about 15% lower than the gross output.


More efficient Modulating Condensing boilers (ModCon) will have efficiency ratings as high as 95% or higher. Those rating plates will show a smaller difference between the Input and NET numbers.
1. So the first thing you get is an accurate load calculation,
2. The second thing is to choose a boiler that will fill that home with that much heat on the design outdoor temperature day (I call it the average “coldest day of the year”) based on the NET rating .
3. The third thing is to get a floor heat design and see how many BTUh of that boiler's output can actually be emitted by the floor.
4. If the floor square footage is not large enough to heat the home on the “coldest day of the year”, then you need to figure out how to get the rest of the heat into that room…
@hot_rod Bob has some suggestions like Radiant tubing in the walls or ceiling, then everything is low temperature. Or you could add another zone with higher temperature panel or baseboard radiators that will activate on a second heat stage of the thermostat (W2),

The microzone problem will be something to address in your design. The ModCom boilers can usually deal well with that once the winter months arrive, but in the fringe spring and fall months, they will be subject to the minimum input of the boiler being much too small for only one small zone calling for heat. The burners will short cycle. this will be inefficient and put additional wear and tear on cycling the burners off and on. The buffer tank idea is the best bet for you zoning choice.

If your contractor is unfamiliar with these concepts, then you may need to find a different one. If he IS familiar with these concepts and also wants to delegate the tubing installation to you along with the manifold design, Then you are a lucky man!

SteamtoHotWater

Download this Idronics issue if you want to learn more about heat transfer in general.

Thank you - downloaded and reading right now.

If he IS familiar with these concepts and also wants to delegate the tubing installation to you along with the manifold design, Then you are a lucky man!

Meeting with him again on Tuesday. Let's hope I'm lucky.

exqheat

I would look at your heat loss from drafts, window loss, attic draft. Be sure you have stopped drafts up the wall cavity to a vented attic. Also consider if the switch to radiant will change the heat profile in the building in cold weather to protect from domestic water freezing.

GroundUp

SteamtoHotWater said:

You can expect a maximum of 25 BTU/sqft of radiant floor.

Got it. Thanks. I'll definitely reevaluate.

In order to zone as you describe, every loop would require a zoning actuator and whichever loops make up a zone would be wired together so they operate together.

That's what I was missing - that multiple actuators can be wired to operate together. Thank you.

Personally I would probably run one manifold set per level and still use actuators on them, which can still be done with one circ if piped properly.

What's the benefit of one manifold per level? Could you also elaborate on how proper piping allows one circulator to operate two manifolds?

Lastly, if my intent is just to keep one bedroom much colder than the others, do I really need a zone, per se? Could I just switch off that loop without any ruining the flow/balance to the rest of the upstairs?

It simplifies the piping as there would only be two lines running to the upper level instead of 8. If one circ runs every time any zone calls for heat, the actuators will keep the remaining loops closed- the same as if there were one manifold set. There isn't really a reason to run two circs.