Basic questions - radiant floors, gas piping

rosio

I moved from Florida and not knowledgeable on heating systems in cold areas. Hoping to get some help here.

I bought a home that has a 1/2" gas pipe coming to my boiler combi unit. While I had a plumber over for another project, he noticed that and indicated it should be a 1" pipe. The boiler turns on, the house is heated just fine. I don't quite understand the implication of using an undersized gas pipe. The plumber said the boiler wouldn't get enough BTU. Does that mean later in the winter on a very cold day, the boiler or heating could fail?

Also what is the normal water temp setting for a tankless hot water/boiler? Should it be running at say 150 degrees most of the time and only go to the max 180 on the coldest days? Are these boilers typically supposed to run 24/7 during the cold months or can I turn it off when not at home like I would a forced air system to save cost.

I have heard that a hot water system is less expensive to run than forced air. However, don't they take a lot of water to run?

What can I expect as far as how warm radiant floors would get? The outside temp is around 30 degrees today. House is very comfortable at 70 degrees but the floors don't feel warm. I was expecting the floors feel warm.

John

justin91

I know that the easiest way to get the floors warmer is just turn the thermostat up. Will obviously use more fuel though...

KC_Jones

Here is a link to a chart about sizing gas pipe. It's a function of connected load and BTU requirements. You can measure your pipe length then compare that to the chart to see what is supported with 1/2". Only measure the 1/2" leading to the appliance. Once you hit a larger size the calculation changes.
http://www.engineeringtoolbox.com/natural-gas-pipe-sizing-d_826.html

Ironman

What make and model of combi boiler do you have? What's the btu rating? It's on the data tag.

"I have heard that a hot water system is less expensive to run than forced air. However, don't they take a lot of water to run?

I'm not sure exactly what you mean by that question. If you're asking "do they waste a lot of water?", then the answer is no. It a closed hydronic loop that should require little or no water to be added once it's filled and properly purged of air. If water is constantly being added to the hydronic loop, there's a leak(s) that should be repaired immediately. In a combi boiler ( if that's what you have), the domestic water is totally separate from the hydronic water.

"What can I expect as far as how warm radiant floors would get? The outside temp is around 30 degrees today. House is very comfortable at 70 degrees but the floors don't feel warm. I was expecting the floors feel warm."

If the floors feel warm, then the supply water is too hot. The floor should feel neutral to bare feet. You're trying to heat your house, not your feet. That fact that it's maintaining 70* is evidence that the system is heating sufficiently.

"I bought a home that has a 1/2" gas pipe coming to my boiler combi unit. While I had a plumber over for another project, he noticed that and indicated it should be a 1" pipe. The boiler turns on, the house is heated just fine. I don't quite understand the implication of using an undersized gas pipe. The plumber said the boiler wouldn't get enough BTU. Does that mean later in the winter on a very cold day, the boiler or heating could fail?"

The size of the gas line depends upon all the appliances connected to it, their total btu demand and the length of the pipe along with the pressure it runs at. That's stating it in simplicity. Charts or formulas are used to determine proper sizing. A 1/2" line sounds a little small if it's of any substantial length, but without knowing the details, it's impossible to say.

"Also what is the normal water temp setting for a tankless hot water/boiler? Should it be running at say 150 degrees most of the time and only go to the max 180 on the coldest days? Are these boilers typically supposed to run 24/7 during the cold months or can I turn it off when not at home like I would a forced air system to save cost."

There's a major difference between a tankless water heater and a boiler. Do you know which one you have? That's why I asked for the model#. A tankless should never be used for space heating, but there are some internet peddlers that push them so they can get a quick sale because they're less expensive than a boiler.

If you have a boiler, then it should be controlling the hydronic water temp based upon outdoor reset. That means it will vary the water temp to match the load. The colder it gets outside, the hotter the water temp and vise versa.

You don't want to turn a hydronic system off and back on or use deep setback, particularly with radiant floors. These systems don't recover quickly like forced air and will operate most efficiently when left at one constant temp on the stat. You'll actually waste fuel and be less comfortable running the stat up and down.

rosio

Thanks Bob. I have a Triangle Challenger 125K BTU tankless combi unit.

rosio

According to the chart, the BTU for the pipe and distance to the boiler is 85K. Much less than the 125K rating. I'm still unclear what this means. The temperature on the combi is showing 170 degrees on a 30 degree day like today. So does it mean that if the temp is 10 degrees outside, the boiler wouldn't be able to put out enough BTU to heat the house even if the water temp got to 180 degrees?

Ironman

What it means (if your calculations are correct) is that the boiler won't get enough gas to fire the burner at 125k btu's. Do you need that much to heat your house. It's doubtful. But without a load calc, we can't tell.
You'll probably be effected more in domestic hot water production where a lot more horsepower is needed than in space heating.
Are you on natural gas or LP?

rosio

I'm on natural gas. I have 2000 sq foot home - 2 stories. At the high end,the calculation was 75K BTU. it sounds like from what you're saying that in the dead on of winter, we won't be able to take any hot showers?

Ironman

The time of year won't matter since the domestic has priority. A 125k btu combi is on the smaller end for producing domestic. You'll notice the deficiency when you try to draw too much hot water at one time. Such as taking multiple showers simultaneously. Remember, the combi works like a tankless heating domestic instantaneously as water passes through it. There is no storage. 125k btu's will get you around 3 gpm domestic production with a 70* temp rise through the boiler. The average shower takes 2gpm of hot water.

Gordy

What type of radiant floors do you have is another question to ask. Poured in slab, gypcrete,staple up.sandwich, suspended tube,plates no plates??

These different radiant floor details all use differing water temps. to achieve the same goal. Your supply water temps is a concern unless its suspended tube or staple up with no plates...or insulation

rosio

This is under the floor staple up from the basement (first floor only) with no plates and no insulation for some reason! I've read that plates and insulation should be added below the floor. I probably will need to add that with a drop ceiling in the basement.

rosio

To Bob - is there a way to know exactly how many BTUs the unit is actually putting out? If my suspicion is correct, and it's only 85K based on the gas pipe size, then for certain at least the gas pipe to the boiler must be larger to even get the 125K capacity.

Gordy

That explains the high supply temps. Insulate, and plate it, and you will use considerably lower SWT thus getting more efficiency out of the boiler. Also use extruded omega plates don't cheap out on the lose fitting beer can plates you will be sorry

Ironman

rosio said:

To Bob - is there a way to know exactly how many BTUs the unit is actually putting out? If my suspicion is correct, and it's only 85K based on the gas pipe size, then for certain at least the gas pipe to the boiler must be larger to even get the 125K capacity.

You can clock the gas meter with only the boiler running on high fire. That would require leaving at least a couple of hot faucets wide open to get it fire at 100%.
You'll have to check with your gas supplier, but a cubic foot natural gas generally has a caloric value of about 1000-1050 btu's per cubic foot.
The smallest dial on the meter usually turns one rev per 1/2 cu. ft. So if you got 2 revs per minute, you'd be at 1000 btu's per minute x 60 = 60k btu's per hour. The boiler's rating is in btu's per hour.

Zman

The advise you are getting from these guys is great.
The one thing I would add is simply checking the gas pressure at the appliance. If you check the pressure with nothing in the house running, then check it again with everything running you will determine whether you have a problem. As long as you meet the manufacture's pressure requirement you should have no issues.
I have seen several incidences, particularly with tankless units, where the gas line is grossly undersized. Everything runs fine until you run the dryer,range, dishwasher and someone takes a shower. All of a sudden the tankless locks out due to low pressure.

Carl

rosio

I am very appreciative of all of the guidance. Thank you all very much. This is a wonderful group and everyone is doing a great service by sharing ideas. I hope I can contribute back in some way.

RobG

As Carl said. If all appliances are running and you maintain minimum pressure at all appliances you are fine (unless your suppliers pressure drops during peak usage periods, but that's a whole other issue). And as Gordy said, extruded plates and insulation are a must for an efficient system. You don't have to put in a drop ceiling, just use insulation supports.

rosio

Can I get any guidance on the optimal temperature that the boiler should run at and what's the max temperature that the floors should not exceed? I'm concerned at the high temp my boiler is running at (170).

SWEI

The floors would ideally be running on constant circulation at a varying temperature determined by an outdoor reset controller. The range of that temperature required depends on the type of plates (if any) the insulation (if any) under them, the subfloor, the flooring, and the floor covering(s) if any.

Zman

Your boiler came with an outdoor air sensor. Is it installed?
To get the maximum efficiency and comfort, you need to have the sensor installed and the outdoor reset configured correctly.
With plateless staple up, you do have to run higher temps. You will have to do a bit of trial and error experimenting to get the temps correct.
I would try running it around 140-150 on the coldest and around 105-115 on the warmest.
170 is very hot, even for plateless.
Check out pages 47 to 49 in the manual

Carl