I'm doing a full reno on my 1000 square foot house and have decided to install in floor heat in the basement and also on the main floor. I'd appreciate some input from the pros before I (potentially) commit to a costly mistake.
I did room by room heat loss calculations and came up with ~16000 btu/hr for the whole house. I've made some running changes to the design that should lower that number a bit but I haven't recalculated. My highest heat loss is the kitchen and it works out to 21.4 btu/hr/ft^2. The lowest is the basement bedrooms at 8.9 btu/hr/ft^2. I'm planning on having 7 loops of 1/2" oxygen barrier PEX, each one 300' long.Basement:
The basement has an existing slab poured over 80% of it. The remaining 20% is crushed rock. The slab is very sloped and has cracks. My plan is to install a dimple board product over the entire floor to act as a moisture/radon barrier and also a thermal break. On top of that will be R10 EPS followed by my PEX loops which will be covered by 2 inches of cement (2" total, only 1.25 inch above the PEX). The plan is to have the cement as the finished floor but I might put carpet/cork etc over the cement in the rec room to avoid trips to the ER with the kids. There will be 3 loops in the basement, 1 for both bedrooms, 1 for the rec room and 1 for the utility room and bathroom. Main Floor
The main floor will have 4 loops, 1 for the Master bedroom, 1 for the 2 bathrooms and walk-in closet, 1 for the living room and 1 for the kitchen. With the exception of the bathrooms, all the flooring will be 3/4" Red Pine. The bathrooms will be tile. I currently have 1" pine for a sub floor run on a 45. My plan is to install sleepers (1x2.5" pine) on the opposite 45 with a 4" gap between them. In that gap I will run the PEX tubing which will then be covered in cement. It will be 1" thick. This is being done for a few reasons, first to provide a method for fastening the finished flooring and second to reduce the overall weight. I considered the aluminum plates in the joist bays but frankly it sounds like a pain and is a fair bit more expensive. I'm also concerned about contraction noises which I'm expecting to be eliminated by having all the PEX in concrete. I will run a layer of sill gasket below the cement/PEX to create a thermal break between the cement and sub floor. The joist cavity will also be insulated with R12 from below.Heat supply
My plan for the remainder of the first year is to run this system off a 50 gallon electric water heater. I plan to install at least 6 50 gallon tanks by next winter. Only 2 of them will be wired up, the remaining are holding tanks. I plan to heat the water during off peak hours and then use the stored heat during peak times. Eventually I want to build a solar water array that will heat the storage water instead of electricity. I may also tie in a wood boiler when the garage gets built which will also be heated by this system.Controls
This is the area that I have the most questions.
My plan was to vary the water temperature in the loops to control my air temperature. Since there is wood over the cement on the main floor I know I need to be mindful of the temperature swings and extremes. Is this as simple as getting a thermostat that has an air and slab sensor and setting my min/max values for the slab?
I was planning on installing my 7 loops on 1 manifold and using manual valves to balance the flow to adjust the temperatures throughout the house. The more I think about this, the more I think it's a bad idea. At the least, I think I need to separate the upstairs from the basement.
Regarding the 6 50 gallon tanks, my plan was to install them in series with each tank supplying the next from the top to the bottom. I plan to feed the injection pump from the top of the last tank and return the water to the bottom of the first tank. I'm hoping that this approach will maximize the thermal stratification. I plan on having a separate pump for the tanks that only activates when the tanks are heating the water. I'm thinking something that will cycle the water at least twice through the tanks during the heating cycle will be sufficient. As for controlling the tank temperature, I was going to use the factory thermostat at the highest setting and then use a timer to ensure that the heating elements don't come on during peak hours. I'm thinking something with outdoor reset might be worthwhile here or I could just manually adjust it each week/month depending on the expected conditions.
I haven't given any significant thought to tying in the solar part since that is likely a year or 2 out. If there is something I should do now to significantly make that easier in the future, I'm all ears. General Questions
- As for air removal, should I install an air bleeder on the top of each tank or is there a better idea?
- I'm planning on filling the system with distilled water. Is this necessary? I have (at present) untested well water or I could haul out some city water (lake fed).
- Should I install any sort of filter on the system?
- Where and what sort of gauges should I install to monitor my system?
- What system pressure should I aim for?
- Would it be sufficient to replace one of the water tank temp/pressure relief valves with one matched for the system pressure? What sort of differential is preferred between system pressure and relief?
I've attached a picture of how I'm currently planning to plumb this up. There are additional valves that I will be installing but I figured I'd redo the picture with more detail once I get some input.