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Radiant Heat - Water Heater Runs Constantly

My closed hot water floor heating system is 7 years old. A few months ago the temp in the house only got to 60 degrees with thermostat set at 74. Bumped thermostat to 80 but still only 60 degrees in house. A plumber came and replaced gauges, put in new bigger pump and finally a brand new water heater. It is now warm in the house BUT the water heater is running 75% of the time -- on for 45 minutes then off for 15 minutes! I've gone through 600 gallons of propane since Jan. 1 and the tank is almost empty again. Yesterday the plumber returned and put in a "loop"? and a splitter. But he can't figure out why the system is running all the time. He blames the contractor that installed the system.

I'm into this for more than $5000 at this point not counting the propane bill at the co-op. Ideas??


Re: Radiant Heat - Water Heater Runs Constantly

Wow! Why did the plumber replace the pump? It seems to me you are getting the flow (the reason for the pump), but not the heat (the water heater) and its delivery system (the loop). As a matter of fact the only thing you are not getting is heat. Go to www.RadiantandHydronics.com and self educate yourself on how your system should work. Look at the diagrams and then look at yours. If you can read a road map, then you can figure where the cold water goes to, and the hot water goes. Without a oicture of what you have there it is hard to say. Alot of hydronics have a boiler, expansion tanks, zones, etc. Good luck. Process of elimination.

Re: Radiant Heat - Water Heater Runs Constantly


There are a number of factors that can account for the situation you describe.

If the system performed ok 7 years ago when it was 1st installed, then slowly deteriorated, then the heater/boiler or some other part of the equipment failed or partially failed, or clogged up.

There are chronic trapped air problems with radiant loops (especially LONG loops); air keeps getting trapped in the tubing, causing poor heat complaints, until the air is purged out of the system.

If the house was hard to heat even when the system was first installed, then it was improperly sized or poorly planned to begin with.

There are a number of factors that determine how much a house needs to keep it warm:

A) location--if you live in a cold northern climate you will need a larger heater/boiler than if you live down South.

B) house size--a 2000 sq.ft. house needs more heat (and a larger heater) than 1000 sq.ft. house.

C) type of construction, windows & insulation-- a well-insulated house in attic & exterior walls, along with relatively new double pane windows will keep a lot more of the heat inside the house, than a drafty house, & thus will require less heat from a furnace or other heat source.

The amount of heat required to heat a house, and the amount of heat that a heating appliance can put out are both measured in btu's/hour (british thermal units/hour).

Houses are usually assigned a btu factor to heat them of between 20 btu/hr per sq.ft. to as much as 70 btu/hr per sq.ft., depending on the tightness, or looseness of the building envelope; this btu factor can be obtained by doing a free HEAT LOSS CALCULATION (below).

The bgm & propane sites are rudimentary; the slant/fin site is comprehensive & can take 2 hours to complete.

Thus, a tight 2000 sq.ft. house X 20 = 40,000btu/hr. (this means a relatively small heater/boiler size of 40,000 btu/hr can adequately heat the house).

The same house that has little or no insulation in the walls & attic & is in a frigid part of the country would need: 2000 sq.ft. X 70 = 140,000 btu/hr to heat the same house.(this would be a much larger boiler/heater & burn much more fuel per heating season).

The strategy in the 2nd case would be to add lots more insulation & install new windows so it wouldn't require such a large heating plant & so much fuel to heat the house.

Other factors involved with radiant heat is A) if the tubing was placed in concrete slabs, was rigid insulation used to reflect the heat upwards to the living space, or was it omitted; was the wrong size tubing used??

B) if the tubing loops exceed 300' the hot water will get cold before it adequately heats the rooms & returns to the boiler/heater, thus the floors & house won't be adequately heated.

C) if the house requires 70,000 btu/hr to heat it, and the water heater or boiler is only rated at 40,000 btu/hr, the house will never get adequately heated, & a lot of money will be spent on fuel.

There are HEAT LOSS CALCULATIONS (Manual J calculations) that are used (sites below) to determine how much heat is required to properly heat a house; these take into account all the factors discussed above.

You should start at the HLC calculations & try to determine how many btu's/hour are needed to heat your house.

Get the square footage of each room (multiply the length X width), including heated cellars, utility rooms, etc., & add them all up to get the total sq. footage of the house.

You can then check the heater the plumber put in to see if it is big enough--its btu rating should be stamped on its housing (something like: "output: 75k btu/hr); you can also Google the heater's model # to get its btu/hr output.

If you need any insulation or new windows (or both)--now is the time to have it done.

For the coming heating seasons, if the present heater continues to return high fuel costs, it may be more econonical if you have a high efficiency condensing variable output boiler installed, such as a Peerless Pinnacle, or a Viessmann vitodens, or Crown Bimini, or Dunkirk Quantum.

These are all about 95% efficient.

You should also do a fuel cost comparison as to how much propane costs in your area, as opposed to #2 fuel oil; there are condensing boilers that can use either fuel.


Re: Radiant Heat - Water Heater Runs Constantly

Thanks for the great information! I am setting out to enlighten myself on the mysteries of radiant heat.

Re: Radiant Heat - Water Heater Runs Constantly

I had the same problem with my oil heater i found the aquastat was set why to high so my heater ran constant check your temp settings on the heater

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