I'm really new at this, so please bare with me..

I live in Toronto and the house is only 10 years old. 
I started last week with finally finishing the basement. 
Currently all my exterior walls are insulated with 6" fiberglass.
I have a walk out basement and my basement slab is uninsulated.  Basement is about 1200 sq/f
I have forced air in the house for Heat and A/C
I'd like to install radiant heating on the basement concrete floor, however I don't want to lose height in the basement.

My questions are:
1.  Should I lay down on the existing concrete 6mm poly, 1" XPS rigid foam, stripped OSB board with heat shields and radiant tubing in between.  The Sandwich System.  I plan on installing ceramic tile in the washroom and laminate or engineered wood on top of the tubing/OSB board.
This will be 1" + 3/4" OSB plus the height of the wood.

or

2.  Should I put down 1 or 2" foam, wire mesh with pex tubing tied to it.  Pour 2" of new concrete. 
This will be about 4-5" of total height.

Will foam or reflective barrier be better?

I'm thinking of a combo boiler unit so it supplies hot water for the house and water for the radiant floor.  What brand would you recommend?  Otherwise a Boiler and a Tankless Water Heater would do as well if you suggest.

Big question, Do I need a heat loss calculation done?  If so why?  I'm installing radiant heating for basement comfort so it's livable full time.
Or can I just lay down 250' max tubing lines all over the basement.   
The house is rectangle, so I'm not having many rooms.

1 room is 13' x 17' (2 small windows)
1 bathroom 9' x 6' ( 1 small window)
1 rec room 23' x 25' (1 small window)

the rest is hallway, mechanical room, mudroom, stairs to upstairs.. (2 exterior doors, 1 leading to the garage the other a walkout, 1 small window)

Thanks for all your help

First, insulating the foundation with a 2x6 studwall with a poly vapor barrier means the studs are subjected to both the ground moisture and any above-grade exposed concrete moisture/splash-back, and can only dry toward the exterior through the above grade portion of the wall. If it's not too late, putting 1.5" of EPS between the 2x6 studs and the foundation and insulating the stud with unfaced fiberglass and NO interior side vapor barrier would be much lower risk.  Putting an inch or more of EPS under the bottom plate as a capillary & thermal break from the slab is worth it too.  With the foam + studwall approach the ~R6 of the EPS is sufficient in your climate to keep the moisture buildup in the stud bays well controlled, since only the above-grade section would ever have a condensation, and the condensing surface would be EPS, which is not damaged by the intermittent haze of condensation that forms during the colder hours.  At 1.5" Type-II EPS (1.5lbs per cubic foot density) has a vapor retardency of about 2 perms, which is lower than the 3-5 perms you'd get out of interior latex paint, so any ground moisture finding it's way in as vapor still leaves, drying toward the interior. If you have at least 15" of above grade exposure on the exterior of the foundation, or an EPDM or metal-flashing capillary break between the concrete and the foundation sill you could even use foil-faced foam, which is more vapor retardent than poly sheeting. 

Using 1.5" of EPS and a 2x4 studwall with R13-15 unfaced batts delivers a higher average or "whole wall" R-value than a 2x6 studwall w/fiberglass and no foam, and it takes up less interior space than a 2x6 studwall.

On the floor stackup it would be better if you put at least 2" of foam, and make it EPS , not XPS. XPS is manufactured with an extremely high global warming impact blowing agent that gives it it's slightly higher R value at any given thickness, but as it leaks out (doing it's damage) over the next 4-5 decades it's R-value drops, eventually hitting the same R value as EPS of similar density.

The OSB subfloor approach will be more moisture susceptible than a 2" concrete mini-slab, but it's fine.  A Roth panel approach will be worth it if you're trying to minimize the overall thickness, since it embeds the tubing in EPS, but it's a cost adder.

Reflective barriers or foil facers have NO useful purpose in this stackup (despite what purveyors of said products might allege.)

Combi boilers even at minimum fire are going to have WAY more heat output than your basement's heat load.  A hydronic loop using a heat exchanger off a hot water heater is a cheaper approach, and won't require to upgrade the gas plumbing (or even the gas meter) to handle the higher-fire of a combi-boiler.  The AO Smith Vertex is even designed with side-ports specifically for this type of application.

The heat load is primarily a function of exposed exterior wall/window area, not the floor area.  The total heat load divided by the available radiant-floor area, and the radiant-floor method used determines the water temp requirements.

If you want to take a pretty-good stab at the rough heat load, get out a measuring tape and start measuring the exterior areas of each sub-type, and we'll come up with reasonable "U-factors" (the average thermal conductivity) for those sub-types from which to calculate the load based on the interior-exterior temperature difference, and the U-factors.

The 99% outside design temp for Toronto is +1F/-17C, and assuming a 70F/21C interior temp, that's a delta-T of 69F, but let's just call 20C or 70F delta just to keep it in round numbers. For the sake of keeping it all in English-unit U-factors and BTU/hour which is more common in N.American HVAC parlance than watts, let's call it 70F.

The U-factor of a clear-glass double pane is about 0.5 BTU/hr per square foot per degree-F. A single pane is about 1 BTU/hr per square foot per degree-F.  So measure up the windows & sliders in square feet and do the math. Assuming your 4 "small windows" are 5 square feet each and all clear double-panes, that's 20 square feet of window of window for window losses of about:

U0.5 x 20' x 70F= 700 BTU/hr.

For fiberglass insulated 2x6 walk-out side figure a U-factor of about 0.078. Measure up the exterior studwall are and do the same math, U-factor x square feet x 70F.

Uninsulated poured concrete has a U-factor of about 1.0 BTU/hr-degree-foot, but only count the above-grade wall area down to about a foot below grade, since that's going to be the bulk of the wall losses- the below grade portion will have losses considerably lower.  If you're adding an interior side  1.5" EPS + batt insulated 2x4 wall, the U-factor will run about 0.06 BTU/hr-degree-foot.  If 1.5" EPS + 2x6/batts, call it U0.05. If just 2x6/batts, U0.75 (slightly better than a regular 2x6 first-floor wall due to a slightly lower framing fraction.)

Any solid wood exterior doors or double-pane glass sliders, figure about U0.5, insulated doors about U0.25.

Ignore the floor losses, and ignore the air-infiltration/ventilation losses, as well as the inputs from warm  mammals, electrical plug loads, duct losses to the basement from the upstairs heating system, etc.

Add up all of the losses for each room by sub-assembly type, then add up all of the room totals, and it'll be close enough for designing a heating system.

If your wall stackups or doors & windows differ from what I've given you U-factors for, tell me what the stackup is and I'll estimate the U-factor for you.

Something else to consider for a minimal loss of height:  Adding 1.5" of EPS to the floor and putting down a 1/2" OSB subfloor tap-conned to the slab, and using a radiant ceiling rather than a radiant floor only blows 2" of height, and is still pretty cushy.  At the likely VERY low per-square foot heat load the difference in floor temperature will hardly be enough to be felt except on the coldest days, and may not be a sufficiently high comfort up-tick to matter or be "worth it" once you've insulated the floor.  That can be determined once we know the total heat load and the amount of radiant floor or ceiling that would be needed to support the load.

Dana, Thank you for the very informative information.

Thanks for all your help.

My experience has been that sooner or later, basement floors get wet. Consider using 1/2" Hardibacker instead of OSB. One layer cut up to allow PEX and plates and then another layer to cover it. Consider putting radiant tubing only where the heat will be noticed (bathroom, areas where people walk and sit). Radiant tubes in other areas just mean that you have to run a lower water temp (ie, less warm in the critical areas).

I broke some concrete in the basement to take a peek underneath. I have a 4” slab, with about 4” of crushed stone and then soil. In around the whole basement.
I’m working out the cost of pouring a thin slab of concrete instead of using OSB with aluminum plates.

Would my setup with a new concrete install be poly, 2” EPS foam and then 1/2” pex with a thin layer of concrete to cover the pex. Can I put hardwood directly on the concrete or would I need a subfloor like plywood. I'm just checking to see how much height I'll be losing in the basement with either concrete or OSB radiant setup.

For the basement with radiant being secondary as the home already has forced air, would you suggest I get a heat load done, a proper pipe design layout and mechanic room parts and units required.
I was quoted for a combo unit about $6000 for an HTR Phoenix Evolution. I'm replacing my existing 50gallon water heater no matter what because it's too small for my household.
What are your suggestions to heat up about 1200 sq'f of basement. Someone said my heat load is about 24000 btu.
Should I go combo, separate units tankless water heat and a boiler?

Should I install 3 thermostats with sensor in the basement or just 1. It's a rectangle room with 1 full bathroom, 1 gym room and large rec room.

Thank you

I broke some concrete in the basement to take a peek underneath. I have a 4” slab, with about 4” of crushed stone and then soil.

Was there a vapor barrier?

We design and install many basement radiant floor retrofits. Nothing goes directly on the concrete but a vapor retarder and/or XPS/EPS depending on the application. We have used several products designed for over-pours, such as CreteHeat, Fast Trak and most especially Roth Radiant Panels, all with integral insulation, vapor retarder and PEX fastener in one.

http://en.allexperts.com/q/Radiant-Floor-Heating-3710/2013/12/1952-concrete-floor-pour.htm

Rehau is a major player in the radiant floor heating market here in Minneapolis and the world. This document may be of some help. WARNING, some people may find pages 5 & 6 extremely upsetting, as they contain explicit details of PEX fastened diirectly to sub-slab insulation in various ways, with wire above all, and may not align with preconceived, and zealously held, notions of common and accepted practice.

http://www.biasew.net/PDF/7-RFHInstallation.pdf

Not upsetting at all since there are way more illustrations with the PEX placed in the middle than there are with the PEX placed on the bottom. Furthermore, Page 4 clearly states that medium thick slabs may have the PEX at bottom or in the middle and that thick slacks should have the PEX in the middle, which further confirms that placing PEX in the middle is the best practice for those people more interested in heating efficiency and green building practices and less interested in cheap and fast building practices.

The less concrete R-value that you have above the PEX, the higher your heating efficiency. The more insulation R-value that you have below the PEX, the higher your heating efficiency. The ratio of the total R-value above the PEX to the total R-value below the PEX determines your overall heating efficiency. While this basic heat transfer principal may be beyond some people’s ability to comprehend and accept (no matter how many designs/installations they hacked), it nevertheless is a fact.

Page 80 also shows protection sleeving installed at control breaks and penetrations for those people who feel this is also an unnecessary practice.

No, there was no vapor barrier.
Radiant heat in my basement will be secondary heat as I currently have forced air.
I don't want to lose lots of height raising the floor.

Option1: Existing Slab with no insulation
Vapor barrier, OSB, pex with heat shield and stripped pieces of OSB sandwich style. Then hardwood everywhere except hallway and bathroom. Can I place hardwood directly on the OSB/pex. Will lose about 2" total

Option2:
Vapor barrier, Duro Foam 2" EPS, sandwich type OSB with heat plates and Pex. Will lose 3 1/4"

Option 3:
Vapor barrier, Bubble wrap or 2"EPS foam, wire mesh with pex attached and concrete pour. Can I lay hardwood directly on top or do I need another OSB subfloor to staple the hardwood. This will be 5" lost

The Roth panel, 3/4" floor or ceiling plus final finish.

There is no practical argument for 2" of rigid insulation on top of an existing basement slab. When we do a complete basement tear-out, removing all concrete, installing new pluming, passive radon, vapor retarder, 2" of XPS tube and concrete, the investment makes sense without the loss of head space. In over-pours with no concern for head space an argument could be made.

The less concrete R-value that you have above the PEX, the higher your heating efficiency.

This depends on the heat source and in many cases (eg, taking heat from a domestic water heater), is incorrect.

Radiant heat in my basement will be secondary heat as I currently have forced air.

Then save some downward heat loss by putting floor heat only where you will notice it.

jonr is right.

In low-load plans such as yours, if the area is open-air the loads can be easily satisfied with local placement of tubing. A radiant specific heat load program can tell you how much insulation, the PEX placement, length and potential output at available EWT.

Thank you for the info.
If I were to go with the sandwich style, which heat shield plates would you recommend.

Heatlink, Omega or ThermaFin.
I'm trying to figure which will not make noise and the PEX tube will snap in. I'll be laying 1/2" pex, are the plates 5/8 opening or 1/2" opening for a 1/2" pex pipe to fit snug.