Possible wood savings with in floor radiant??

[dspoon19]

After doing some reading this winter I have realized that running radiant loops under the floor would provide a better, more even heat. I have read that it's around 25% more effecient than a forced air system. I was hoping someone on here could validate that 25% approximation and also tell me if that efficiency increase will lead to 25% less wood consumption. Currently I run my forced air system with 180 degree infeed water and around 162 return water temps. I go through just about 1.75 cords on average per month durning heating season.

Any info would be a big help!! Thanks!

 

[Bob Rohr]

Sounds a bit high, you will still need to run the boiler hot enough to assure return temperature protection, maybe 150F as the lowest temperature.

Savings really depends on the design and installation. Generous insulation is required under slab, floors, and especially around the edge of a slab or rim joist.

A proper design and load calc is needed. I have seen radiant jobs that were under-tubed and they run non-stop and still do not provide comfort.

 

[tom in maine]

I think some of that savings is dependent on the building heat load. Radiant might offer more savings when the building has a higher heat load, but as Bob said, you cannot skimp on tubing. I think 10-15% is more likely average savings.
In a retrofit, a radiant panel system could be more effective, more comfortable and less cost. It is also a LOT quicker to install. And you can design the system to work with lower temperature water, which is a big plus when working off thermal storage.

 

[maple1]

How good or bad your forced air system is also comes into play, I would think. Lots of potential for heat loss in an air duct, depending on the space it is running through & how the insulation is.

 

[BadgerBoilerMN]

You first radiate to be comfortable. This is the most valuable part of any radiant heating system. Second for me is the quiet. If properly installed radiant heat is silent. Finally, one can achieve unmatched comfort vs. cost of operation with radiant heat by matching the heat source to the radiant panel.

Forced air will require a minimum supply water temperature, first to meet the heat load and second to keep the wind chill manageable. To this we maintain 130° SWT at our fan coils. This is also the minimum return water temperature for all but condensing boilers.

Real savings are had in the shoulder seasons using outdoor reset. With the right controls you can maintain a hot storage tank or boiler while using the minimum water temperature needed to satisfy the heat load at any given time. Outdoor reset is the key.

If you are going to install a sub-floor heating system a room-by-room heat load with some modeling software would be in order to assure the floor will heat the space. We use extruded aluminum plates on nearly every sub-floor system we design or install.

 

[peakbagger]

I agree that 25% is going to be hard to peg down as its so dependent on your installation. If you have typical forced air ductwork that is leaky, poorly or not insulated and runs outside of the conditioned space, the number could be higher.

 

[black_sab]

You first radiate to be comfortable. This is the most valuable part of any radiant heating system. Second for me is the quiet. If properly installed radiant heat is silent. Finally, one can achieve unmatched comfort vs. cost of operation with radiant heat by matching the heat source to the radiant panel.

Forced air will require a minimum supply water temperature, first to meet the heat load and second to keep the wind chill manageable. To this we maintain 130° SWT at our fan coils. This is also the minimum return water temperature for all but condensing boilers.

Real savings are had in the shoulder seasons using outdoor reset. With the right controls you can maintain a hot storage tank or boiler while using the minimum water temperature needed to satisfy the heat load at any given time. Outdoor reset is the key.

If you are going to install a sub-floor heating system a room-by-room heat load with some modeling software would be in order to assure the floor will heat the space. We use extruded aluminum plates on nearly every sub-floor system we design or install.

Hi BadgerBoiler ,

Have you retrofitted the aluminum plate solution in really old houses with success?

I'm looking at an early 1800 house. You can see glimmers of daylight from the basement between some of the floorboards. I'm wondering if radiant in a floor like this is asking for an expansion/contraction nightmare with the old wide plank floors.

FHA throughout, would be nice to have radiant on the 1st floor for comfort during the day since the floorboards are exposed in the basement for ease of installation and get the FHA into the second floor.... then again the FHA vents are close to the furnace so the most heat loss would conceivably be in the runs to the second floor.

Also wondering if NOT pumping hot air through those 1st floor ducts during the cold would rob the basement of the heat needed to keep the pipes from freezing.

 

[BadgerBoilerMN]

First, a room-by-room ACCA Manual 'J' will answer your questions. We have installed thousands of feet of aluminum sub-floor plates to heat old homes, just finished 1886 renovation in Minneapolis. I heated my brother's 4-square with a suspended tube system, before plates were invented. 5" southern yellow pine still perfect after 20 years...

Whether plates are for you depends on the heat load and the output of the installed plates, heat source, control system etc. We also design and install many hybrid radiant-forced air systems but this takes a level of experience rare in the industry. Design help is the first step.

 

[black_sab]

First, a room-by-room ACCA Manual 'J' will answer your questions. We have installed thousands of feet of aluminum sub-floor plates to heat old homes, just finished 1886 renovation in Minneapolis. I heated my brother's 4-square with a suspended tube system, before plates were invented. 5" southern yellow pine still perfect after 20 years...

Whether plates are for you depends on the heat load and the output of the installed plates, heat source, control system etc. We also design and install many hybrid radiant-forced air systems but this takes a level of experience rare in the industry. Design help is the first step.

Thanks for the reply. I downloaded the free MJ8ae .xmls sheet, apparently for dummies like myself. I'm not well versed in this stuff AT ALL. but it wouldn't hurt to play around with parameters and see what the variation in the numbers the tool spits out.

 

[moey]

Forced air is no less efficient. Where the efficiency comes into play is the delivery and design of the system. Forced air systems often go through uninsulated space often have lousy insulation on them if any often create pressure differences in the house which results in pulling in outside air in extreme cases. Its much easier to put insulation on a 3/4 pipe then a 10 inch duct. So the 25% is very difficult to measure as its very design subjective.

 

[black_sab]

Forced air is no less efficient. Where the efficiency comes into play is the delivery and design of the system. Forced air systems often go through uninsulated space often have lousy insulation on them if any often create pressure differences in the house which results in pulling in outside air in extreme cases. Its much easier to put insulation on a 3/4 pipe then a 10 inch duct. So the 25% is very difficult to measure as its very design subjective.

I've been in a handful of houses that had it. Just wasn't a fan of the unevenness of the heat with the room coming up to temp... dropping temp... blower comes on... coming up.. rinse and repeat.

And how the heck can you tell the quality of an FHA duct run install that's hidden in a wall that traverses 3 stories? inspection camera?

 

[arbutus]

Badger is spot on. I retrofitted aluminum plates and pex under the first floor and panel radiators in the second floor two winters ago, replacing electric baseboard.

The house always feels toasty, and the floor is never cold.

 

[JP11]

I think every house would be different. I bet in my application I save a bunch. Living room ceiling is 18+ feet at the peak. If I were heating the air... it would be awful hot up there.

Radiant floor just cruises along. I did radiant for several reasons

1. I hated the old, cheap forced hot air in our previous house.
Noisy, Dusty, uneven heat.

2. It makes room decoration that much easier. No worrying about a couch against the wall blocking a baseboard.

3. The comfort factor is top notch. even heat that you never even think of.

 

[black_sab]

I think every house would be different. I bet in my application I save a bunch. Living room ceiling is 18+ feet at the peak. If I were heating the air... it would be awful hot up there.

Radiant floor just cruises along. I did radiant for several reasons

1. I hated the old, cheap forced hot air in our previous house.
Noisy, Dusty, uneven heat.

2. It makes room decoration that much easier. No worrying about a couch against the wall blocking a baseboard.

3. The comfort factor is top notch. even heat that you never even think of.

JP11,

Did you do 100% radiant throughout? or just where you could access the floor from the basement?

 

[JP11]

Whole house. did it as it was new construction. My upstairs is stapled up with the wide wirsbo stapler made for pipe (it's about a 2 inch wide staple that holds it to the subfloor, but allows some side to side shifting)

No transfer plates. 8" on center between pipes. It's got an inch of air space below the pipes, then 2" foil faced foam. Pipes run at about 140 degrees. Whole house above is either tile, or laminate floor. Works great, not a complaint in the world.

JP