In floor heating vs. radiant vs. forced air in shop??

[laurencen]

Boilers are great, the one I put in is high efficency, I have 8 zones all of which can be adjusted, for instance, the uility area and bathroom are 10 degrees different, the exercise room and sitting area also are set different, it takes a wile to get it set but what a great setup, I doubt a hot water heater can work this good, the boler setup was little over 4K, It took 2 weeks to get from -20C but now hardly varies, If I had a fan to circulate the rest of the house figure the air handling system would rarely be required

 

[mjncad]

As I understand it, boilers are generally used for traditional hydronic heat using radiant baseboard radiators, while the water heaters are better suited for the lower temperature in-floor radiant heat.

Boilers generally provide 180F water, while water heaters are in the 120F range.

Note, the water heaters used for in-floor heat are not your typical units found at Home Despot.

Check www.radiantech.com for more info.

 

[woodlandfarms]

One of the things I have wondered and have never heard first hand experience from is that I like to sleep in a cold bedroom. So, what I am hearing is that if you are on a slab, it is at least 2 hours of heat radiance, so you would want to cut the supply of heat off at 8 and start it up at 6A assuming normal sleep patterns?

Just wondering what experience people who have radiant in floor heat can share...

 

[Egon]

One of the things I have wondered and have never heard first hand experience from is that I like to sleep in a cold bedroom.

Come live at "Old Crow" in an outfitters tent for a year. You will get first hand experience!

The "Cold Experience" will depend on the wood supply and the willingness to exit the sleeping blankets to fuel the stove.

Heat may be attained but not retained obtaining next years supply of firewood!

 

[patrick_g]

One of the things I have wondered and have never heard first hand experience from is that I like to sleep in a cold bedroom. So, what I am hearing is that if you are on a slab, it is at least 2 hours of heat radiance, so you would want to cut the supply of heat off at 8 and start it up at 6A assuming normal sleep patterns?

Just wondering what experience people who have radiant in floor heat can share...

I have in-slab heat in my great room, including kitchen, (a tad over 1000 sq ft.) while in the master suite Nother 1000 plus, I have a mix. The bedroom proper has in ceiling radiant (pex behind drywall) while the master bath has in slab and the shower has in slab plus in-wall and is on its own stat which has a sensor in the tile grout of the wall so it controls the floor and wall temp not the air temp.

The sitting room has forced air plus a direct vent propane decorative parlor stove (gas log.) The walk-in closets have no heat. OK they are heated, but indirectly. We have a HRV unit with 4 registers to collect the outgoing air stream. One of these registers is in the ceiling of the far corner of the walk-in closet. Warm air from the rest of the house passes through the bedroom into the walk-in closet via a bypass register (with filter) in the wall and is exhausted to the outdoors. In winter the closets are a degree or two below the bedroom temp.

All the parts of the house with in floor or in ceiling hydronic heat also have, in addition to the zone stats for hydronic control, programmable set back stats for the forced air (heating or cooling.) My geothermal heat pump can provide chilled air, heated air, heated water, or hot air and hot water at the same time. you can set the air stat a degree or two below the hydronic stat and if the outside temp drops fast so that the hydronic lag makes the floor fall behind then the hot air kicks in till the floor catches up.

A hydronic ceiling for the bedroom has worked out very well indeed. We wanted a good carpet in the bedroom and the R-factor would have interfered with a hydronic slab. Much of the bedroom is covered by the bed and furniture which would interfere with heating. The ceiling is never obscured by anything and if you were not aware the heat was in the ceiling you couldn't tell. The room is just comfortable. It cools or heats faster as the sheetrock has a low R-value and much less thermal mass than a slab. The slab under the carpet is insulated underneath and ends to maintain the average room temp or close to it.

If you want to be able to more quickly change the temp of the room with hydronics, go with a hydronic ceiling with a carpeted area or both hydronic ceiling and floor in a tiled area. If you want to sleep in a cool room but have it warm in the day then go radiant ceiling, hydronics or otherwise.

Pat

 

[DRL]

Woodlandfarms,
I to like to sleep in a cool bedroom. The last house I built (just sold recently, ready to move on) I had heat in the floor throughout. The master bedroom was on its own zone, usually set at about 60-62. The master bath also on its own zone with its thermostat having a probe in the floor, keep at about 74. The rest of the house, several zones were keep at about 70. No setback thermostats. It was wonderful. you could leave the doors wide open and the temp difference was very noticeable.

DRL

 

[gerard]

All that being said, What I plan on doing is setting the radiant heat to 40 degrees and keeping it there. so the shop & contents wont be freezing, etc...and when I want to work in the shop I'll manually turn up the T-Stat on the hot air and use that to take the chill out of the air...best of both worlds.

I have a friend with a 40x40 shop that he recently insulated. He doesn't heat it and the place still maintains a 40deg temp just from the heat radiating up from the floor and the ground beneath it. I would question going through the expense of radiant floor heating if you only plan on heating it to 40deg. The heat will probably hardly ever come on?? That said I think radiant floor is the way to go. Puts the heat where you need it and thermal mass works both ways, it takes a while to heat up the mass but it also takes a while to cool down.

 

[patrick_g]

A late post script to previous message: The thermal time constant of an in-slab hydronic system depends on several things, among which are:

(incomplete list)

1. Btu/hour available to heat the water,
2. diameter of PEX,
3. length of runs,
4. spacing of runs,
5. flow rate,
6. water temp,
7. heat loss of the space being heated in Btu/hour/degree of differential between indoor and outdoor temps,
8. thickness of the slab,
9. location of pex within slab

The simple model of a room heated by in-slab hydronics considers two basic heat quantities typically measured in Btu/hour. One is how many Btu/hour does the room lose out through the envelope (walls/ceiling/floor/windows) at some particular delta T (temperature difference between indoors and out.) The other is how many Btu/hour can you "pump" into the room?

The thermal inertia of the slab is acted upon by the input heat supplied by the hot water to raise the slab temp. How fast you can raise the slab temp is proportional to the number of Btu you can transfer into the slab and inversely proportional to the slabs thermal mass.

If you heat the space 24-7 to about the same temp then you only need to be able to deliver enough heat to the slab to raise it above the room temp sufficiently such that it sheds the same number of Btu into the room as the room is losing to the outside through the envelope. If you have the capability of delivering this amount of heat constantly under the coldest outside temps of interest and the highest indoors temp of interest (maximum delta T) then your system is capable enough.

This "minimal" acceptable system will not raise the temp of a cold room very fast. It would be very uneconomical to install enough water heating capacity and water circulating capacity to try to get anywhere near the speed of heating a cold room achieved by forced air. Still, when heating a space 24-7 this is a very practical system and will give great comfort except when the outside temp varies rapidly over a large range.

My solution to this "shortcoming" was that since I had to have ducts for summer cooling I have the ability to get hot air to supplement the slab heat. Then if the temps plummet the floor will be comfortably warm and the air temp will be kept by the hot air delivery. Then when the temp rises the hot air shuts off automatically and the floor does the total job. if the temp shoots uP while the slab is near or at its max temp then the house will overheat. Some folks even run the AC to compensate. A better strategy is that since the overheating is typically in the "shoulder seasons" you just use less floor heat and more forced air during periods of widely fluctuating outside temps in the spring or ... Then the floor is not overheated but the space is comfortable due to some floor heating (I like going barefoot on tile floors in winter) with the difference made up with hot air.

Sleeping in a cool room is attractive to a fair percent of us. In-ceiling hydronics (or in-ceiling radiant heat from any methodology) reacts much faster that in-slab hydronics. The thermal mass of the sheet rock is way less than the slab. The R-value of the sheet rock is very low and does little to insulate the heat delivered from the PEX. While setback thermostats are useless with in-slab, they make sense with a proper in-ceiling installation.

You will never be happy with the room temp in a bedroom with in-slab heat if you want it cool at night and warm during the day. Shutting down the heat does not drop the room temp any where near fast enough to let you get the desired effect by shutting down a couple hours in advance. The slabs great thermal mass results in a time constant so slow that it will just not respond sufficiently within a few hours. To try to get the desired effect will just end up with a room at some average temp between your desired daytime and nighttime temps and you won't be happy being cool all day and too warm all night.

If you just warm the floor sufficiently to make it comfortable and supply the rest of the heat with another (faster) method such as forced air, a parlor stove (direct vent gas log which is attractive and practical and safe) then you turn off the supplemental heat a while before bed time and you will get much closer to what you want. In-ceiling radiant (hydronics, electric, or...) gives a much faster response than in-slab. I have it and it works fine for me.

Another thing... cathedral ceilings and open plans (great room etc.) let hot air rise to ceiling and requires a fan to stir this air and get it down to the floor level and may feel drafty. With in-slab heat (radiant heat) much less of the heat is lost to convection (estimated 30 % instead of way more) You tend to heat the occupants way more than the ceiling. My HVAC operating costs are on a par with and often lower than other heat pump equipped homes less than (sometimes considerably less than) 1/2 the sq ft of my "barn." (over 5000 sqft not including over 1800 sq ft of attached shops one of which is two story)

Pat

 

[woodlandfarms]

This is quite interesting info, for both shop and home.

I am assuming that there would be no cooling benefit from radiant floor design. Meaning, in the summer, run the tubes instead of through a solar collector, through a pond or underground.

I have been reading a lot lately that cooling a house is more of a concern to architects than heating (in terms of cost reduction / energy efficiency).

So, what about a more energy efficient cooling? I would think this is just as important as the radiant heat in the winter.

 

[kmdigital]

My garage/workshop is very similar to yours, 32'x40', metal clad, 12'ceilings and a 10' garage door. Mine is insulated and drywalled with a concrete floor. I have a natural gas radiant direct vent wall heater. http://www.cozyheaters.com/pdfs/products/spec_sheets/DirectVent.pdf
Mark

Sorry, but that's not a radiant heater. It is a simple convection heater, with a very minimal radiant output. Radiant heat is line-of-sight, and it is not affected by air, distance or space. It does not give up it's heat until it strikes a surface that can absorb it, in turn warming that surface. This warm surface in turn heats the air around it.

Don't believe me? Then tell me, how does the sun heat the earth, even though it is millions of miles away? That is why space craft have to slowly rotate, as the side towards the sun get very hot, while the dark side temperatures are close to absolute zero. (Wow, think about the stresses on the metal from the two extremes)

Radiant tube heaters work the same way, with the rays striking the floor or other surfaces, warming them, which then heats the air. However, they do also have some convective heating effect since the tubes are hot, they will heat the air around them.

Floor heat is hard to beat, and no, assuming that you put antifreeze of some sort in them, you don't have to heat them forever after in a shop application. You can use it when needed or leave it off for the entire season. But don't expect rapid temperature changes.