Hey all - I'm new to the forum but thanks for any help!

I'm currently building out a radiant floor heating system in my 4 floor 3200 sq ft home, and most of it seems to make sense but I have one specific question that will affect the cost of the system.

I have 7 zones configured, which will all be centrally zoned at the main manifold where the boiler is. I plan on running a single PEX line for each zone to the floor that needs it - do I require a manifold for each zone to manage the circuits within the zone? Would these secondary manifolds need to have balance adjustments, air releases and such? With 7 zones, and roughly $200 per manifold it starts to add up quickly.

Here is an example of the manifold I'm talking about: Amazon

Not sure if I'm over-complicating the setup, or a simple tee would work to distribute the circuits over the zone.

Certainly lots of ways to do this. The hot water line leaving the heating source (or tank) can have branches for each zone. That branch will run to the zone manifold that will distribute the water. You can have a big pump for all the zones or 1 small pump per branch that will push the water to the manifolds. The manifolds can have adjustability so if your runs are not all the same length the flow differential can be adjusted for each run coming off the manifold.

These questions can't be answered without careful consideration of the floor plan.

Thanks thescottcav - that's pretty much what I had in my head as a requirement. I understand the problems with head pressure and I do think it will make sense in my case to do a small pump per floor (lower floors on the return side, higher floors on the supply side) to overcome these issues having to deal with 4 floors. The equipment is located centrally in the middle-most floor to minimize this.

The circuits are not the exactly the same length due to layout, and are each less than 200 feet. I think in this case it would be best to have an adjustable manifold on each zone that has more than one circuit.

Highly unlikely.

Most residences can be heated with a single pump. Vertical height has no bearing on pump specification. Zones can be controlled by valve or actuator. The loop lengths you used will have no bearing on manifold or pump selection.

The more pumps you use the more electricity you waste.

I understand that a single properly rated pump would also suffice, but how on earth does vertical height have no bearing on pump specification? That's precisely what head pressure is, as I understand it. I'm not quite sure what your advice is ;)

The system is closed loop (i.e. NOT open to the atmosphere someplace). The pump drives the water up and gravity drives it down. So elevation head is not a factor in a closed loop system…only hydraulic friction head is a factor…and what governs the size and how many pumps are required. The longer the circuit and the higher the circulation rate, the higher the hydraulic friction and the greater the need for more pumping head. If the system were open loop (i.e., open to the atmosphere someplace), then elevation head would be a factor.

There are a number of installers who will place a manifold in the basement and run lines direct to each floor, saving separate manifolds on each floor. Personally I think this is cheating and it makes it difficult to get all the air out of system. The proper method is to have one manifold (minimum) per floor which works well for the average house. Things change if that floor is 5000ft2 but not if it is 1000ft2. There are options to this but it is most common and allows for balancing, air elimination, and, if desired, a pump for each floor. It can result in way more pumps than needed for the heat loss.

My experience is that too many zones on a floor is a waste of materials. Unless the floor has some areas with very different heat losses, such as a north side with very little window area vs a sunroom, on t-stat is going to be as comfortable as multiple stats, especially if the tubing is in cement. The vast majority of my clients set the stat and tend to forget about them.

The power needed in a closed loop is mainly to overcome the friction of pipe, elbows and valves etc. They are called circulators because all they do is create a small pressure difference between the input and output. This is enough to overcome the resistance within the piping and start flow. Height is irrelevant to this. 

MikeSolar - thanks that was very informative. Really great information from everyone, I'm learning lots I'm planning on no more than 2 zones per floor, but considering to drop some floors down to one zone. For me it was a choice to leave seldom used rooms unheated, but I'm not sure the cost savings is there since the rooms are relatively small.

You might benefit from reading John Siegenthaler’s “Modern Hydronic Heating”, particularly chapter 10 “Hydronic Radiant Panel Heating”, which provides the step-by-step design details. A good portion of this great book is available for free reading on Amazon.com and there are also places called libraries where it can borrowed and read for free. You will first need to determine your room-by-room or zone-by-zone heat loss analysis and book keep the exposed floor heat loss separately before accomplishing this design. We have both heat loss analysis and hydronic radiant floor heating design software on our website for free DIY use. Don’t forget that you will need an expansion tank and we have design software for that on our website as well. Good luck with your project.

Unless the floor has some areas with very different heat losses, such as a north side with very little window area vs a sunroom, one t-stat is going to be as comfortable as multiple stats

I have one thermostat for the entire house and have never had enough problem with unbalance to bother to add more. It's ducted hot air, but the principles are similar to radiant with a single thermostat and many adjustable valves. If I had significant solar gain and closed doors, I'd add more thermostats.

Wow that book looks fantastic! It's a bit pricey, but given the volume of material I'm going to check it out. Maybe I can even find one of those things you call a "library" - I've heard my parents talk about them from the good ol' days.