How to heat garage slab radiant floor?

Caleb

Trying to help a friend here with new construction.. Installing mini split electrics in apartment above garage, but just poured cement floor with pex installed for radiant flooring. But how to heat the water in floor? Would like electric installation as there is no gas/ oil at the property, but cost of electricity is pretty high.. maybe supplement with solar hot water? Or install propane tank and gas heater.. Can we use instant how water heater for radiant floor heating?

This is in southern New England, cold winters, but milder than Vermont/Maine.. more like NYC weather

36' x 40' 3 bay garage floor to heat, 6 radiant loops installed already. Need ideas how to heat the floor?

Another friend here has wood/oil furnace and heats his basement floor with hot water from the wood stove, but trying to stay away from requiring wood fire or oil to heat the garage floor..

Suggestions for heating this system?

thanks!

SWEI

Heat loss calculation? Fuel costs? In many areas, LPG prices are very close to electric. Electric boilers generally cost less to buy, and since you don't have to run gas or flue pipes, the install costs are also lower in most cases.

Caleb

Do I really need an electric boiler since I am only heating to ~100 deg? My gas boilers go to 180*F.. thought a lower heat water heater would suffice..??

I have heat calc... not sure final R value of 3 garage doors, but estimating 26K BTU through structure, plus 10K Infiltration.. 36K BTU total.

Caleb

Looks like electric is the way to go.. Any comments on the Stiebel Eltron Hydro-Smart solution? http://www.hydro-smartwholesale.com/HydroShark3.html

bobde

I use propane on demand hot water heater made by Takagi- it worked great last year-I am located just east of Buffalo so it is cold-my garage is about 40x 60 and I have 6 runs

Ironman

Your system needs to have outdoor reset to control the water temp based on outdoor temp. Otherwise, it will over-heat due to the high mass of the slab which will give off heat long after the stat is satisfied.
ODR, when properly set will deliver just the right supply water temp to the floor as the heat loss increases or decreases.
Make sure you choose an actual BOILER, not a water heater. Water heaters are not designed or controlled for space heating and they have way too much head (flow resistance) for hydronic application.
A boiler will have an ASME "H" stamp meaning it's designed and approved for space heating. If it doesn't have the "H" stamp, it is NOT a boiler - no matter what the internet peddler calls it.

Caleb

Thanks all. I talked to hydro smart and they said the Tempra micro boiler by stiebel eltron is UL rated as a boiler under UL834 certification.. http://www.hydro-smartwholesale.com/HydroShark3.html

Therefore its rated as a "boiler" and comes with 2 year warranty. Though I am suspicious as I know the duty cycle is much different than just a DHW heater..

Any idea how to calculate electricity cost of heating a concrete slab? I calculate 16K btu's, which is 4800 watt-hrs, but how many hours a month is the system estimated to be on?

Zman

This is good way to compare energy costs http://www.eia.gov/tools/faqs/heatcalc.xls

Rich_49

About 4,228 Kw annually . Check your rates and use 4228 Kw based on last year heating degree days from Niagara Falls Airport . Using .10 per , you're at 422.80 yearly . Your actual rates may be higher or lower .

Bob Bona_4

I have used the Steibels for domestic..unbeleivable performance. One case was a 2 bath house, with typical 50 gall tub in one, shower in another.

120 amp feed however. Oof.

I would be looking at the smallest lp mod con with ODR here though for my region-CT.

Caleb

Rich said:

About 4,228 Kw annually . Check your rates and use 4228 Kw based on last year heating degree days from Niagara Falls Airport . Using .10 per , you're at 422.80 yearly . Your actual rates may be higher or lower .

Rick, how do you compute 4228 KW? My electricity is 18.5 cents/KWHr

Is it worth buying all the LPG tank and equipment for Connecticut winters? LP is around $3.20/gal

Caleb

deleted

Rich_49

Sorry bout the mistake in location , wrong post , thought Buffalo , but in either case . Translate therms to Kws , that's how . 1 Kw = 3414 BTUh . 1 therm = 100,000 BTUh .
1 gallon of propane = 91,800 BTU = 3.20 or 488.02 Season
26.889 therms = 4.97 or 757.95 Season .
Unless you go with an AWHP with a nice COP .

Whether or not it's worth it is up to you . Probably be cheaper to move .

Caleb

AWHP = air to water heap pump?

If its 17,000 BTU/hr heat loss that's 5.1 KWH, times 24 hours times 30 days, at 18.5cents/KWH, that $687 per month. sound right?

ha, cheaper to move, yea, copy that

Bob Bona_4

2.19 lp fill up lower sw ct today. Usually the lp supplier does the tank set and sometimes the line to appliance.

Caleb

OK, can someone recommend a micro gas boiler for radiant heated floor? I have 20K BTU/hr max coldest night in January. 13K BTU average (30 deg outside, 70 deg inside) month of January. This would be LP source with above ground tank outside

Rich_49

Caleb , what kind of water heater do you have ? COP for Heat pump is acronym for Coefficient of performance ., for every dollar you spend it should make 4.00 worth of heat . Your calc also must include a factor that every hour is not design , for your area that factor would be .605 .

NYplumber

Look into a Pellergy boiler system.

Caleb

Rick, what is the factor called you said is 0.605? a daily use factor?

Its new construction so no mechanicals installed yet. We were thinking mini splits for apartment upstairs, electric on demand hot water for DHW. And not sure about radiant heated garage floor.. Looking at CT around $0.20 / kWH, thinking adding LP gas may be best for radiant and DHW. Probably separate systems to avoid using stagnant radiant hot water for showering, cooking, etc.

Rich_49

Correction factor is what it is called , and for 5250 HDD it is .605 , for 7750 HDD it is .645 . DOE states that roughly 47% of annual fuel use is for space heating . Took all that into account when I posted your numbers . But now you say this is a new structure that has living area above that also has DHW . This is a much different ballgame when thinking " What do I do ?"
Give us some more info on the upstairs also and what EXACTLY it will be .
Trying to design this yourself with our help will be much easier with all the information . What systems are in the existing house now would also open up the dicussion to be productive .

Robert O'Connor_12

is this going to be living space or is it a garage? figures are close but that's for living space. if just trying to take edge off it won't cost that much. I'd go with the propane....or move
Robert O'Connor/NJ

SWEI

Smallest mod/con of which I am currently aware is the Lochinvar CDN040. Nice price, too.

Caleb

Robert O'Connor said:

is this going to be living space or is it a garage? figures are close but that's for living space. if just trying to take edge off it won't cost that much. I'd go with the propane....or move
Robert O'Connor/NJ

Sorry if I didn't explain more. My first sentence of the post said new construction of garage / apartment. But basically it's a 3 car garage with apartment above it. Free standing, not connected to a main house, no other buildings on property (yet).

Garage is 36'x42'. 12' wall height. Apartment is 42'x24'. 4 ft knee walls, open ceiling 12/12 pitch. 14' ceiling in center.

Slab is poured with 6 radiant pex tube circuits and a manifold. Trying to decide on heating slab, DHW for upstairs apt, and heat/cool apartment.

Thanks!