I will be installing hydronic radiant heat in my home with some help from family and friends. I am brand new to radiant and I've been doing some research. My plan is attached. I need help revising it and making it better. I'm after a good balance between low upfront cost and energy efficiency. After some feedback I'd like to have a solid purchase list that fits my needs. I have natural gas and public water, also looking for a domestic hot water heater so I was looking into a Navien-combi unit. This is a retrofit project. Thanks!

Your plan in general looks fine. In lieu of two 2-loop and one 4-loop separate manifolds and three zone valves, you might want to consider a single eight loop manifold and eight loop actuators.

Upfront cost and efficiency will largely be determined by the type of HR emitter you construct and the heat source you select. A concrete slab emitter often is both the lowest cost and highest efficiency. A below-floor plate HR emitter is the often the highest cost and lowest efficiency. An above-floor HR emitter is somewhere in between these. A heat pump based heat source is the highest efficiency (really the highest coefficient of performance and the lowest operational cost), but also has the highest acquisition cost. An electric boiler is 100% efficient (but only has about one third the coefficient of performance of a heat pump based heat source) and often has the lowest acquisition cost while also being very robust (i.e., long life and low maintenance cost). Electric boilers are also easy to DIY install and setup. Some electric boilers like the NextGen boiler are also HR plug and play and can save a lot of HR component expense and hassle:

NextGen Boiler

A condensing gas boiler is similar to an electric boiler, but is not as robust and I don’t know of any available in the states that are HR plug and play. As your home becomes more energy efficient (i.e., better insulated and sealed), heat source efficiency (or coefficient of performance) becomes less important because your operational cost becomes quite small in any event. So a ROI analysis is really needed to make the best economic selection.

John Siegenthaler’s “Modern Hydronic Heating” is a great source of everything you need to know about this subject.

How big are your loops and the size of your house? What percent of the house will be heated floors? All?

I am a fan of having 3 pumps instead of 3 zoning valves. Cost is almost the same and helps in balancing out your flow better.

But the above comment of having one pump and one manifold is an option if your house balances heat out good, but you wont have/need multiple thermostats. If you don't mind that.

I have two houses with heated floors throughout and planned on having multiple thermostats in the new house(we are almost done with construction). I am finding that I am able to control the house with one thermostat so might go that route to save cost. The house is 7000 square feet and I never thought I could get it to work with just the manifold and flow actuators.

Good Luck.

The attachment indicated that this house size is 1300 sf. This is why I suggested that a single centrally located manifold might be something to consider. Loop length for 1/2" PEX tube should never exceed 300 feet. So using 12" PEX tube spacing in a 1300 sf house could be accomplished with a minimum of 5 loops. However, separate rooms and such often creates the need for more smaller loops.

Best practice is to use the minimum amount of flow rate and pumping that is needed to maintain the design delta T (i.e., the difference between the supply and return temperatures in each loop). Typically, a design delta T of 15F is specified for residential HR applications and this is usually adequate to eliminate any floor surface temperature gradients that can be detected by bare feet. Typically, less than 0.5 GPM per loop is needed to accomplish this. Pumping at higher flow rates than this creates higher hydraulic friction head which requires bigger pumps. Bigger pumps and more than one pump uses significantly more electrical power than is really needed. Pumps tend to have the highest HR component failure rate and they should be cycled for at least 10 minutes every day even during the non-heating seasons to help prolong life and avoid having a seized pump when heating season begins.

Zoning is a complicated subject and how best to accomplish this can only be determined by a room-by-room heat loss analysis. And room-by-room doesn’t just mean rooms with walls around them. A “room” could be an area in a great room that is in close proximity to large windows. Basically, areas in the building that have significantly different Btu/sf requirements from the building average Btu/sf are candidates for having a different PEX tube spacing and a separate zone. Yes, it is best to minimize zoning for cost reasons, but you do need the capability to provide different heating levels where it is needed when it is needed.