Hydronic heat not as efficient as forced air ?

Gordy

The only thing I can come up with at this point is that when you were on forced air, and not radiant besides the radiant supplementing some heat until the slab lost energy. Is the forced air may be running a bit less because it’s heating the air, and not the mass of the structure so the thermostat gets satisfied more quickly. Thus runs more frequently. The forced air unit is probably less btu input than the boiler also. Just a guess on that. Even though it cycles more it’s probably still not running as much total time as the boiler.

Gordy

But I’ll bet the forced air comfort is not the same as the radiant......

lucky

No the forced air heat is not as comfortable and I was shocked to find out that the radiant heat was not as efficient as forced air in my specific case. But thanks to all the help I got on this forum I now know the reasons why:

1. No outdoor reset installed
2. Boiler loop piping is undersized
3. Space heating water temp was set too high

lucky

I should add that another advantage of radiant heat is that during a recent power outage that lasted for several hours, we still had a toasty warm house with heat radiating from the floor the whole time.

Gordy

I thought you might say that. My post about what I came up with was in addition to what you just listed.

Gordy

Air can heat faster because it’s not heating the mass of the structure. It also loses that energy faster. Mass is your friend with the right control strategy.

Solid_Fuel_Man

If you are at 120 now, you can drop that to 110, and then by 2 deg a week until it won't keep up. Once you get the outdoor reset tuned, it should run "call for heat" most of the day unless there is significant solar gain during the day. 12 hour run times are not uncommon.

Larry Weingarten

Hello, It still wouldn't be an apples to apples comparison, but closer to it: How about running the radiant for two weeks and track energy usage for each week. Now heat loss is the dominant factor for the second week, rather than bringing the mass of the house up to temp. This would give you numbers to compare first and second weeks and also (once the mass had cooled) you could again measure your forced air system energy usage to compare.

Yours, Larry

Gordy

It would also be interesting to see which system burns less fuel when things get down, and dirty at the design temp.

Above where the forced air must supplement.

Yes @Larry Weingarten is right a week is a pretty short time frame for the radiant. About the time it reaches thermo equilibrium you are pulling the plug on it.

lucky

When I did the test, radiant heat had been on for 3 weeks prior to starting the test to make sure the mass was already warmed up before I measured the natural gas used by the boiler. I knew the test would not be fair if the radiant heat side of the test had to warm a cold slab as well as account for heat loss. Both sides of the test had the benefit of a warmed slab, in other words both the radiant heat and the furnace side of the test would have had higher usage numbers if the mass was not already warmed up.

lucky

I did more measuring with the IR temp gun today right after the thermostat stopped calling for heat. The center of the inside floor was at about 74 degrees but the outside edge of the floor next to by the outside facing walls was running closer to 78 degrees, I was surprised to see the outside edge be so much warmer.

Gordy

You probably have tubing close to the wall perimeter.
Also perimeter insulation.
You can use that IR gun to actually find tube centers after a heat call is over is the best time. Be patient. Get close to floor, and slowly run it across. When the temp reaches the highest that’s where it is. It may take a bit to find which way they run unless you already know.

Voyager

Brewbeer said:

I converted my forced air house to hot water baseboard in 2015. Both the furnace and the boiler were/are high-efficiency units. With several years of data before and after, there isn't an appreciable difference in the amount of natural gas consumed, whether forced air or HWBB.

The BIG difference is in the comfort level.

And I'm happy to pay more for a heating system that is noiseless, consistent, even, and draft-free. There is nothing more annoying than having to turn up the TV when the heat comes on.

I used to think that about FA heat also, but it was based on growing up in mobile homes and then living in a house with a poorly designed FA system. When I built my log house in 2000, I considered all types of systems, but wanted AC and the HVAC company I worked with said that FA was the best option to include AC. When I voiced my objections, I was assured that a properly designed forced air system would not be drafty, noisy or have 3-4 degree temperature variations between on and off as I was accustomed to.

I decided to trust the company designer and go with forced air. I have no regrets. The Lennox Elite furnaces (I have three due to the house architecture and log construction) have work nearly flawlessly for 18 years (had one early circuit board failure) and the comfort level is fantastic. Unless the house is completely silent, with nobody else home and no radio or TV on, I can’t tell when the system comes on. The house has twice as many registers per room as my former home and a return in every single room. The air flow through the registers is relatively slow which minimizes drafts and noise. And the Honeywell t-stats cycle the furnaces something like 6 times each hour which keeps the temperature within a 1.4 degree range, setpoint +/- 0.7 degree.

My only regret is not putting hydronic in my basement slab as the water heater that was installed to provide enough heat for my Jazuzzi, has ports for space heating so I would not have had to buy a boiler to have a more comfortably basement.

I recently commissioned a boiler in my 32’x48’ workshop to drive the in-slab pex. So far, the system works great, but I have found it thus far impossible to maintain a consistent temperature during the day/night cycles here in PA. We often swing 30 degrees from day to night and when set at 60, the slab will heat the building to as much as 65 during the day when maintained at 60 during the night even though the boiler does not fire once during daylight hours. Outdoor reset is installed and the water temps are pretty low, typically 80 supply and 60-65 return. I am hoping the Smart Response thermostat is still learning, but it doesn’t seem to be getting any better at timing the boiler firing to prevent the daily overshoot. And I suspect that with this much thermal mass there is simply no way to avoid a several degree swing when the outdoor temps vary 30 degrees in 12 hours or less. I think physics simply won’t allow otherwise.

The comfort level is great in both my house any my workshop. I think proper design and installation of the system trumps system type. A well-designed FA system is superbly comfortable. I think the same is true for hydronic. FA has its drawbacks such as high temp variation from floor to ceiling just as hydronic has issues with slow response (baseboard and in-slab) and overshoot (in-slab). So, no perfect system, but properly designed and installed, both systems can deliver the goods efficiently.

Zman

lucky said:

No the forced air heat is not as comfortable and I was shocked to find out that the radiant heat was not as efficient as forced air in my specific case. But thanks to all the help I got on this forum I now know the reasons why:

1. No outdoor reset installed
2. Boiler loop piping is undersized
3. Space heating water temp was set too high

My guess would be:

1. No tracking of actual temp, wind, or sun.
2. Flywheel effect of overheated slab.
3. Bean counter trying to quantify a subject he or she does not understand.

Maybe I missed something but I can't find any real data in any of these posts....

Gordy

Voyager said:

Brewbeer said:

I converted my forced air house to hot water baseboard in 2015. Both the furnace and the boiler were/are high-efficiency units. With several years of data before and after, there isn't an appreciable difference in the amount of natural gas consumed, whether forced air or HWBB.

The BIG difference is in the comfort level.

And I'm happy to pay more for a heating system that is noiseless, consistent, even, and draft-free. There is nothing more annoying than having to turn up the TV when the heat comes on.

I used to think that about FA heat also, but it was based on growing up in mobile homes and then living in a house with a poorly designed FA system. When I built my log house in 2000, I considered all types of systems, but wanted AC and the HVAC company I worked with said that FA was the best option to include AC. When I voiced my objections, I was assured that a properly designed forced air system would not be drafty, noisy or have 3-4 degree temperature variations between on and off as I was accustomed to.

I decided to trust the company designer and go with forced air. I have no regrets. The Lennox Elite furnaces (I have three due to the house architecture and log construction) have work nearly flawlessly for 18 years (had one early circuit board failure) and the comfort level is fantastic. Unless the house is completely silent, with nobody else home and no radio or TV on, I can’t tell when the system comes on. The house has twice as many registers per room as my former home and a return in every single room. The air flow through the registers is relatively slow which minimizes drafts and noise. And the Honeywell t-stats cycle the furnaces something like 6 times each hour which keeps the temperature within a 1.4 degree range, setpoint +/- 0.7 degree.

My only regret is not putting hydronic in my basement slab as the water heater that was installed to provide enough heat for my Jazuzzi, has ports for space heating so I would not have had to buy a boiler to have a more comfortably basement.

I recently commissioned a boiler in my 32’x48’ workshop to drive the in-slab pex. So far, the system works great, but I have found it thus far impossible to maintain a consistent temperature during the day/night cycles here in PA. We often swing 30 degrees from day to night and when set at 60, the slab will heat the building to as much as 65 during the day when maintained at 60 during the night even though the boiler does not fire once during daylight hours. Outdoor reset is installed and the water temps are pretty low, typically 80 supply and 60-65 return. I am hoping the Smart Response thermostat is still learning, but it doesn’t seem to be getting any better at timing the boiler firing to prevent the daily overshoot. And I suspect that with this much thermal mass there is simply no way to avoid a several degree swing when the outdoor temps vary 30 degrees in 12 hours or less. I think physics simply won’t allow otherwise.

The comfort level is great in both my house any my workshop. I think proper design and installation of the system trumps system type. A well-designed FA system is superbly comfortable. I think the same is true for hydronic. FA has its drawbacks such as high temp variation from floor to ceiling just as hydronic has issues with slow response (baseboard and in-slab) and overshoot (in-slab). So, no perfect system, but properly designed and installed, both systems can deliver the goods efficiently.

As I said earlier I can’t remember a situation on this site like this where a home owner had both types of systems. And compared them.

I find this interesting if it can be done properly. It needs to be verified both systems are as properly designed, and executed through installation as can be. Along with construction data of the structure. Then a proper comparison analysis could be done.

Steamhead

Gordy said:

As I said earlier I can’t remember a situation on this site like this where a home owner had both types of systems. And compared them.

I find this interesting if it can be done properly. It needs to be verified both systems are as properly designed, and executed through installation as can be. Along with construction data of the structure. Then a proper comparison analysis could be done.

Don't forget to include STEAM in this comparison!

Gordy

Steamhead said:

Gordy said:

As I said earlier I can’t remember a situation on this site like this where a home owner had both types of systems. And compared them.

I find this interesting if it can be done properly. It needs to be verified both systems are as properly designed, and executed through installation as can be. Along with construction data of the structure. Then a proper comparison analysis could be done.

Don't forget to include STEAM in this comparison!

I’d welcome that.

ratio

FA, with similar thermostat settings, can not raise the temp of the slab to a temperature comparable to that of the radiant system. It's always going to be a heat sink when using FA, just like it's always going to be a heat source when using the radiant. IDK the mass involved, but I wouldn't be surprised if it took several weeks or more after changing from radiant to FA before the heat stored in the slab isn't statistically noticeable, especially if it is properly insulated.

To do a somewhat valid comparison between the two, it's just about imperative to do it over a season & adjust for degree days. & after that, how much of the difference is due to less than optimal design &| install of either system?

That said, I'd be looking for why the radiant used soooo much more fuel. Something's not right.

ChrisJ

The only way to test it is to leave the radiant off until the slab temperature stablize without it. And then somehow try to compare usage vs HDD.

Fact is there's no free ride. Forced air may end up cheaper in that building due to many reasons.

But it'll never be as comfortable.

Something many seem to forget is the main reason you're running a heating system is comfort.

You're never going to get the same level of comfort from forced air especially in a building on a slab.

My kitchen is over a crawl space. Even with cast iron radiators cooking, that room feels cold when the floor is 40f. I need to fix some bad drafts and do some insulating. That aside, the room would be far worse with forced air. It would be beautiful with radiant in the floor but it would cost more due to all of the loss into the drafty crawl space.

BennyV

For the OP, I didn't see anyone mention the possibility of using both systems in parallel. If the radiant system's ODR curve is set just below what it needs to maintain temperature, and the scorched air is set a few degrees below the setpoint of the radiant, then the radiant will always be on, BTUs will always being going into the slab, and the scorched air can make up any difference on a particularly cold or windy day or whatever.

I despise scorched air or hydro air systems that are the only source of heat, however. They are just uncomfortable. There's an extremely narrow window between setting it at, say 60, and being cold, and 64 where you're sweating. Further, houses with upstairs zones that come down from the ceiling and downstairs zones from the floor are always fighting gravity, the downstairs fights gravity in the summer, the upstairs in the winter.

I actually don't mind electric baseboard for comfort, as it has room by room control, but that only works economically in a smallish apartment. My ultimate would be an outdoor reset microzoned system that used radiant for kitchens, bathrooms, and hallways, and low-temp cast iron radiation everywhere else (wall to wall carpeting doesn't work well with radiant).

hot_rod

It is sometimes nice, or necessary to move some air for humidity and IAQ, maybe that could be done with the FA, in addition to the radiant.

Voyager

hot rod_7 said:

It is sometimes nice, or necessary to move some air for humidity and IAQ, maybe that could be done with the FA, in addition to the radiant.

If money was no object, I would have radiant floor heat and keep it at a low level just to keep the floors neutral feeling to bare feet (I think something in the 70s is enough for this) and forced air for AC, humidification, air quality management (ERV/HRV) and general heating. I think that would be the best overall solution, although more costly than using just a single heating technology.

hot_rod

Yeah, when we talk comfort radiant is just part of the solution, Need to keep the home healthy, turn some air, filter add or remove humidity. Especially in todays tight homes.

lucky

BennyV said:

For the OP, I didn't see anyone mention the possibility of using both systems in parallel. If the radiant system's ODR curve is set just below what it needs to maintain temperature, and the scorched air is set a few degrees below the setpoint of the radiant, then the radiant will always be on, BTUs will always being going into the slab, and the scorched air can make up any difference on a particularly cold or windy day or whatever.

I despise scorched air or hydro air systems that are the only source of heat, however. They are just uncomfortable. There's an extremely narrow window between setting it at, say 60, and being cold, and 64 where you're sweating. Further, houses with upstairs zones that come down from the ceiling and downstairs zones from the floor are always fighting gravity, the downstairs fights gravity in the summer, the upstairs in the winter.

I actually don't mind electric baseboard for comfort, as it has room by room control, but that only works economically in a smallish apartment. My ultimate would be an outdoor reset microzoned system that used radiant for kitchens, bathrooms, and hallways, and low-temp cast iron radiation everywhere else (wall to wall carpeting doesn't work well with radiant).

Yes, I have the forced air temp set a couple degrees below the radiant temp so on those exttremely cold days where the radiant cant heat the slab up fast enough, the forced air should kick in to keep the house warm while the slab heats up. So far I have not seen that happen but it is set up to handle that situation when it does happen.

kcopp

Have you installed the outdoor sensor yet? It will help the system adjust accordingly instead of guessing at the load...