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Plans to use a hot water heater for 900 SQ FT Home

moussa Member Posts: 3
Afternoon everyone,

I am going to try to give as much info as I possibly can, hopefully someone reading this can give me some advice.

My plan is to install hydronic radient floor heat under the subfloor between the joists in the basement using 1/2 pex with 02 barrier, 2ft Aluminum heat transfer plates. I am using 1 1/4 GRK screws to affix the transfer plates to the subfloor. I am using a copper manifold containing (4) 1/2" inlets and (4) 1/2" outlets. The main feed to the copper manifolds are 3/4"

My subfloor consists of 1" thick hardwood it has 30 mil underlayment on top and finally 9/16th bamboo tung and grove board on top.

I plan on using my current HOT WATER HEATER, not the boiler to heat the home. It is a 40 gallon unit, which will eventually be replaced with a 60 or 75 gallon unit.

The hot water heater will feed a TACO stainless steel circulator pump controlled by a TACO SR501 single zone relay. which is controlled by the thermostat.

Each run on the manifold will be approx 225 Ft.

My home is approx 900 SQ FT, not a very large home. Single floor with an attic. No insulation in Attic. Construction is Solid Brick over block. There is no insulation in the walls, Home was built in the 20's. Steel lath and concrete over the brick, plaster over the concrete.

I plan on Insulating the Attic in the next 2 weeks with R-30 fiberglass

I am using a very small 1,500 watt ceramic heater now which gets the living room, dining room and kitchen to 72 degrees when the outdoor temp is below 40. These 3 rooms are approx 500 Sq Ft. My hope is to have the indoor temp be a constant 67-70 degrees by using the floor heat.

The house used to have baseboard heat, it was removed when the new floors went down.

How do you think this set up will fair?


  • Gordy
    Gordy Member Posts: 9,546
    Open system Not recommended

    Your design, or ides is an open system which mixes potable water with heating water. Play ground for legionella .

    First you need to do a heat loss to see if plated under floor will provide enough output for the max water temp the water heater could achieve.

    Second IF it is achievable you need to use a hx to separate potable from heating water.

    Third a water heater Will not be very efficient maybe 65-70% tops to do the job.

    Plus side you used plates.
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