Heat source for radiant?

[Ict57]

Built a new garage, approx 950 sq ft and ran about 800 ft of 1/2” pex across 4 zones.

I’m in KS with mild-ish winters, usually 0 is about the coldest we get and it’s a working garage that’ll be relatively well insulated.

My question, contemplating a point of use type electric heater (gas isn’t an option). Any suggestions or concerns? Do I need to use a normal tank style heater? Or a big(ger) tankless?

Thanks, trying to get drywall up and need to figure what kind of wire to run.

 

[anythingyoucanimagine]

Built a new garage, approx 950 sq ft and ran about 800 ft of 1/2” pex across 4 zones.

I’m in KS with mild-ish winters, usually 0 is about the coldest we get and it’s a working garage that’ll be relatively well insulated.

My question, contemplating a point of use type electric heater (gas isn’t an option). Any suggestions or concerns? Do I need to use a normal tank style heater? Or a big(ger) tankless?

Thanks, trying to get drywall up and need to figure what kind of wire to run.

Would you consider oil? Typically with radiant you want the supply to be in the 90's... 95 degrees F (or so....). In all of the radiant systems I've seen it's always been glycol based hydronic. The additives carry less BTUs so figuring it out can get tricky (for sizing boiler).

I've seen people use everything from traditional non-condensing boilers with mixing valves to electrically heated (wall mount) heaters to traditional domestic hot water tanks.

I'm not sure how a hot water tank would work. Mechanically it's easy, supply on one side, return on the other and put a circ pump/pumps somewhere. I'm more talking about the tanks rebound time and ability to heat and/or keep the radiant fluid warm enough to work.

Have you done radiant before? They call it a "flywheel effect". Like how a car's flywheel has inertia, it takes a LONG time for a radiant slab to change temps. Not sure how a traditional hot water heater would handle that. We did a 13x20 addition to our house last summer with in-slab radiant. We have solar panels on our roof so I did a medium-efficient on-wall, tankless electric heater for it.

Hopefully someone more knowledgeable than me will comment. I'd think a small-ish, fairly efficient electric hot water heater wouldn't be terrible. You'd have to learn to balance the circ pump cycling vs. the hot water tank ONLY heating what's in the tank.

On the plus side, if you run a hydronic with additive in a hot water tank intended for domestic water, I'd think it would last an incredibly long time because it'll be a closed system so no sediments and outside variables. Fill it up with distilled h20 plus additive. Use an expansion tank to regulate system pressure and call it a day.

Hope that helps.

 

[HoosierBuddy]

I personally would not run a radiant system on a point of use electric water heater in Kansas.

I would fear the water heater would not be able to keep up and would run constantly and the high cost of power to a resistance heating element would eat me alive.

A much better option (IF you want to or need to stay with an electric source) would be a heat pump based solution. That may steer you away from radiant. The upside is the same unit would give you cooling in the summer time. Energy cost would be reduced by 75% or more.

Good luck!

Phil

 

[4 FN 27]

Check with you power company to see what kind of programs they offer that can get you a discount.

I know my provider offers a "Back-up Relief Program":

https://www.xcelenergy.com/programs_and_rebates/residential_programs_and_rebates/heating_and_cooling/back-up_relief_program

I pay $0.50 on the dollar. 10K sq ft heated for $189 and some change this winter for the highest bill...

You may have to make a bigger upfront investment but for me the savings is worth it. My system paid for itself in 4.8 years.

Remember it is big corporate so keep digging...use them.

 

[Highbeam]

All electric resistance heaters are 100% efficient. A little heater running 24/7 but doing the job will use the same amount of electricity as a larger heater running part time. There is no wasted energy except for the small wattage for the circ pumps.

 

[anythingyoucanimagine]

Don't have much info so I'll try to put numbers to this:

Built a new garage, approx 950 sq ft and ran about 800 ft of 1/2” pex across 4 zones.

800ft of 1/2" is 1,885 cu/in which is 8.16 gallons. 4 zones means 2-gal per zone. If you do tankless, throw in another (guess: 1-gal per zone) for other stuff and that bumps you up to 12-gal, 3-gal per zone.

How tall are the ceilings? What does "relatively well insulated" mean?

To make numbers easy I did 30x30 which is 900sf. (31x31 is 961) With 10-foot ceilings and a 50-degree desired temp change (that was a guess but probably fine at 85% efficient), you'd want 42,000 BTU/hour or a 12,308 Watt system.

You could probably get away with something like this:

https://www.lowes.com/pd/MAREY-ECO-...GPM-Tankless-Electric-Water-Heater/1000027127

Again, only issue I see would be your return temps and whether or not the thing is running 24/7 during cold months. At $200/each I might consider buying two and run them in series. (almost to pre-heat the return side)...

Have you sized your circ pump(s) yet? Is this one open slab with 4 zones for heat distribution or four separate tstat temp controlled zones?

 

[Ict57]

Thanks for the very thorough response!

It’s actually 28x28 with an attached 20x8 entry (think 36x28 less an 8x8 notch) on 6” slab. Has 2x4 walls with r13 that are 10 tall with vault peaking at 13’. Ceiling has r38. Windows doors and garage door are insulated. Have 4 loops but only plan 1 zone, will degrade flow on non essential loops. I’d be happy with 55-60 degree temps in winter. Don’t need 24x7 hot, just taking the edge off.

Haven’t spec’ed pumps yet.

I was looking at very similar heater and like the 2-phase approach. Mainly after a basic plan for sake of running wire.

 

[finn]

All electric resistance heaters are 100% efficient. A little heater running 24/7 but doing the job will use the same amount of electricity as a larger heater running part time. There is no wasted energy except for the small wattage for the circ pumps.

You are correct. Big or small, resistance heating is all roughly the same efficiency.

Hoosier is also correct, in that a heat pump will be more efficient, within its designed operating temperature range, than a conventional resistance heater.

 

[xyster101]

I just fired up my radiant floor in Jan. If you are doing all electric, don't do radient floor heat, get a heat pump. You put 1 unit of energy into electric heat, you get 1 unit of heat. You put 1 unit into a heat pump and you can get 1.5 units of heat because it is moving heat from outside in (winter) or inside out (summer).
If you do radiant you need propane to do a tankless or tank system or oil for a boiler system.
I went tankless due to the price ($500) and ease of installation. The floor will have a huge swing time. If I want to warm the shop 5 degrees, I have to turn it on and wait 2 hours. By the time the place warms up 5 degrees, it ends up another 5 degrees in 2 hours. It does melt snow off vehicles and dry the floor nicely. The floor is warmer then the ceiling. I have R-30 in the walls (2x6) and 49 in the ceiling. Upstate NY has cold winters though.
Check out my review if you are really interested in radiant:

 

[Ict57]

I just fired up my radiant floor in Jan. If you are doing all electric, don't do radient floor heat, get a heat pump. You put 1 unit of energy into electric heat, you get 1 unit of heat. You put 1 unit into a heat pump and you can get 1.5 units of heat e of installation. ceiling. Upstate NY has cold winters though.

Thanks, radiant is new for me...and heat pumps are just that more foreign. I’ll start looking around but any other suggestions for where to start?

 

[yeldogt]

In a large open space with high ceilings ... radiant will allow for some ongoing operating savings over forced air ... but don't expect huge savings. You will be more comfortable at any given temp.

Modern mini-split heat pumps are often operating at 3x resistance -- so they can have a real savings over straight resistance .... plus you get AC. Splits are in the 2.5 range.

The OP needs to do a heat load on his building so he understands the BTU's needed for the space and using that heating load he can determine what electric heat in his area will cost. In most parts of the country electric is the most expensive -- but, not all. It's all up to what he pays. Also -- he needs to determine if a water heater will have the BTU output he needs.

 

[finn]

I’ve said this before, and stand by it: Radiant is great for maintaining temperature in a shop and the warm floor is comfortable for many, but not all people, but it isn’t so good for a building that isn’t continually occupied, because of the slow response time to heat the area from freeze protect to comfortable working environment temperature.

I keep my building in the mid forties all winter with the propane fired radiant, and use a hanging forced air propane heater to bump the temperature when I am actually in the shop. One could do the same with an appropriately sized mini split, I suppose.

It would be cheaper to avoid the radiant and its associated cost all together in my opinion.

 

[anythingyoucanimagine]

It would be cheaper to avoid the radiant and its associated cost all together in my opinion.

Yes but if you don't have a lift it is SO NICE!

 

[yeldogt]

I’ve said this before, and stand by it: Radiant is great for maintaining temperature in a shop and the warm floor is comfortable for many, but not all people, but it isn’t so good for a building that isn’t continually occupied, because of the slow response time to heat the area from freeze protect to comfortable working environment temperature.

I keep my building in the mid forties all winter with the propane fired radiant, and use a hanging forced air propane heater to bump the temperature when I am actually in the shop. One could do the same with an appropriately sized mini split, I suppose.

It would be cheaper to avoid the radiant and its associated cost all together in my opinion.

All correct.

There is much about radiant that people don't understand. Radiant works best in a well insulated building with a properly designed system. As the heat load per foot increases (poor insulation / leaky building) the temp of the water increase and then naturally the floor temp. If you work low on the floor all the time this can get too warm.

You don't install radiant to save money .. and, you can certainly make a comfortable garage w/o it.

With 12" spacing a slab is going to require a couple hours to bring it up 20 degrees -- that's why if you want a fast response 8" or even 6" is required. I always do 6" inside my homes when doing a slab on the lower level.

Someone trying to do a building on the cheap is up against all the problems. Typically they don't want to spend the money on insulation and air sealing -- they want to minimize the loops of PEX ... they are concerned about fuel costs so they plan on low temp building when not occupied. More often then not --- they pick less than best heat source. It's all working against a happy system and owner.

For those lucky enough to have NG -- a well insulated building with radiant is not going to be all that expensive to maintain -- so 12" will be fine. I still do 8' and specialized layouts if the space is large.

Heat Pumps don't like set backs -- the cost to bring a space up to temp can near the cost of maintaining it depending on space and unit.

 

[Ict57]

Sorry folks but I’m new to this...and a bit dim.

Any suggestions on a air to water heat pump? I’m open to alternatives to a simple electric tankless unit. And I’m half tempted to use a lesser heat source and keep the floor cooler maintaining ambient at 40-45, then use a traditional source to warm up when I’m out there.

Or even better, would love the ability to push cold water through floor when it’s hot.

Honestly I, pretty open but already to committed to the 1/2” per on 10-12” spacing and NG isn’t an option. Else suggestions are welcome!

 

[Ict57]

Starting to think about simplicity of a mr cool diy type unit. Seems many folks have had good luck with them!?

 

[xyster101]

As I said, if you are set on radiant floor heat, get propane as your heat source.

Heat pump is a fancy word for Air Conditioner. Think of putting a window AC unit in backwards so it blows the exhaust (warm) air into the living space. A heat pump is just that, a AC unit that moves heat either from outside (even when it is 5 degrees) to inside. You will need a HVAC person to install it as it has refrigerant in it and requires some special tools. You don't have to be scared, call some HVAC companies and ask them about it. They should be able to do free quotes for you.
Look up Mr. Cool as those are DIY "heat pumps".

 

[yeldogt]

Starting to think about simplicity of a mr cool diy type unit. Seems many folks have had good luck with them!?

What's your electric cost ?

What's you heat load ?


with a heat pump you can't keep a cold building and expect a fast warm up -- they just don't work that way... they also have limits as far as temp range.

It's all about the BTU's ... unless you know what you need you can't make an educated decision.

Air to water heat pumps are around -- but, as they are not common -- they are expensive. I have expensive electric .. so propane is my only choice. The cost of the air to water for radiant is no big savings when you look at lifetime costs.

You have to do some homework

 

[HoosierBuddy]

I want to modify my original advice based on what yeldogt pointed out....because he is right. I would only suggest a heat pump if you plan to heat it 24X7X winter. If you are only wanting intermittent heat, then a heat pump is not your best solution and radiant is OUT.

For most people, the cheapest way (by far) to heat a garage is part time with some type of unit heater. There are about 720 hours in a month. If you only run your heat 12 hours every weekend, that is going to mean you only heat your building 7% of the time. That is going to cut your cost vs heating it all month by roughly a factor of 10. At that point, your cost of energy per unit doesn't matter nearly as much.

So...for those people, an oversized unit heater of any kind will typically get the job done. Oversized so it can bring the heat up quickly. Your energy source could be propane or electric in your case. If NG was available...that would be even better.

Phil

 

[86turbodsl]

Real good advice here from yeldogt and finn. Listen to them.

Radiant is really nice, but you really want to be using your building a lot to make it worth the while.

 

[Randy in Maine]

My radiant heat is cheap to run on propane (and to me propane is $2.49 a gallon). I am not out there every day but my tools and my stuff is.