What size water heater for 200sf system?

craigwillis

Your professional opinion will be appreciated.
What size water heater should i use on the below described system?
200sf area, heat loss of less than 9,000 btu/hr, 1/2” pex staple up w/ transfer plates, 2 loops of 150’ (300lf total), single zone, crawlspace installation, north missouri, crawlspace to be insulated, joist bays to be insulated.
See attached photo for reference.

My questions are:
What size tank style water heater should i use? Due to space it needs to be a short 30 gallon or less.
What size elements?

Robert O'Brien

200 Sq/ft? 9000BTU heat loss? 45 BTU per sq/ft? Heat loss is incorrect and if by some miracle it isn't, you can't get 45 BTU out of a sq/ft of floor surface..... without being able to fry eggs on it!

Zman

I agree with @Robert O'Brien .
That being said. To covert from Btu's to watts, divide by 3.412. Keep in mind that electric water heater will only run element at a time so you only want to calculate the output of one element, not both.

hot_rod

200 X 25 btu/sq.ft. realistic output per square foot = 5000 btu/hr

An electric tank with a 1500W element= 1500 X 3.41= 5115 btu/hr.

Most small, off the shelf 6 or 10 gallon tanks have a single, 1650W 120V element, 5626 btu/hr

HVACNUT

Is this an addition to your home? What's the primary heat source? Warm air?

craigwillis

Thank you gentlemen for your replies! Mr. Rohr, thank you for answering both of my questions so directly. That is the information I was needing.

craigwillis

HVACNUT,
This is a tiny house/cabin quality built, small but very nice. The primary heat will be the radiant floor heat. Previously was heated by a 10,000 btu wall mounted lp gas heater.
On low would run you out, and my son keeps his bedroom window open as that heat was not good for a loft bedroom.
thanks!
And, I am fully aware that a wall mounted gas heater should not be used a primary source of heat. This will become backup only in case of power outage.

hot_rod

really no sense in putting more radiant "heat source" in, then the floor can comfortably distribute. Mid 20's (btu/ sq. ft.) is a generally agreed on output for radiant floors once furniture, etc is in place.

With electric tanks, an inexpensive element change-out can quickly increase or decrease output.

Modulating electric boilers are another option for an appliance that could adjust it's output to the ever-changing load.