Furnace and/or Boiler

Barry

Thanks for the reply. Yes it is a 93% condensing unit. What makes the hydronic more confortable? Is it because there is no blowing?

Barry

Furnace and/or Boiler

I live in a 1923 house with a boiler and radiators. We recently had central air installed. Instead of adding an air handler I opted for a furnace since we had room and it was not much more expensive. Now we have two fully independant heat systems. The boiler is 83% efficient and the funace 93% efficient. Will using the furnace be more efficient overall? My wife would like to get rid of the radiators but I am not sure what system would be more efficient overall. Any other advantages/disadvantages to either system? Thanks

mark ransley

You will save using the furnace, electric will be more running a blower, gas will be less. it is a 93% condensing unit? I would not remove the other system, radiator heat is quiet and more comfortable to me, its a backup now. With the furnace you can now easily humidify the air.

Brad White_185

What tends to make hydronic heating more comfortable

than most air systems is a complex set of variables.

I think that the dominant one most people sense is the radiant effect, line of sight IR radiation beaming toward you and blanketing the walls (in the case of baseboard, maybe not what you have) with a layer of warm air between you and otherwise cool walls.

Other variables have to do with the Mean Radiant Temperature (MRT), an amalgam of surface temperatures of your body, the inside surfaces of the walls and the room temperature itself. (Having good glazing and good insulation raises all of these regardless of system used.)

A good (well distributed) air system can be more comfortable than a poorly distributed hydronic system, let's be frank here.

If the warm air is supplied low and toward the exterior while your comparable system has radiators on the interior core, you will be more comfortable with the air system.

The other reason that many air systems are deemed to be less comfortable goes to their operating sequence. Traditionally the furnace fires, temperature is made once the plenum is warmed and only then would the fan start. Once the thermostat is satisfied, the burner shuts off and the fan runs until the plenum temperature drops. Once that happens, most occupants would feel a chill as the heat is off and the warm air barrier disappeared. Again, good insulation and a tight house lessen this greatly.

Constant air circulation (and in a hydronic system, constant water circulation for that matter) can greatly increase perceived comfort.

Much more to it than that, but those are some key points.

don_192

I must say

I must say,that is the best reply I have ever herd here on
this issue.

Thanks Brad.You're the man.

Unknown

Brad most condsensing

furnaces do not use plenum temperature anymore to bring the fan on. They are time on time off using either Electronic Fan Timers or Integrated Furnace Controls which when added to an existing ducts system with inadequate returns means blowing cold air when it comes on and cold air when it shuts off. The condensing furnaces also blow air which is about 120 degrees most of the time which is 20 degrees below the temperature that the old furnaces had for duct temperature.

One more very important item with warm air is adequate return air which should be 1 1/2 times the supply side for good air movement add to that a controlled blower speed with an ECM type motor and warm air can be very comfortable.

I have been running my 56 year old GE furnace on constant air circulation for 38 years now and in combination with a powerpile gas valve and 6 returns it works great.

The Pellet stove added 8 years ago has been an even greater plus.

Steamhead (in transit)

Don't forget

the typical duct system is very leaky- duct systems lose an average 20% of what goes into them. This reduces the over-all efficiency of the furnace. Yes, there are new, improved duct joint seals but I have yet to see a duct system that was perfectly sealed. Go here for more:

http://oikos.com/esb/28/duct_losses.html

Also, unless the supply and return in each room are well balanced, a duct system can pressurize or depressurize the various rooms in the house. This increases infiltration and exfiltration. Go here:

http://oikos.com/esb/44/forcedair.html

Sure, the furnace itself might have a 93% AFUE, but what's the advantage if the heat is not transported to the rooms efficiently?

Keep your radiators. Are they steam or hot-water?

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Barry

Thanks for the reply. My radiators are hot water. I am a little worried about pressurization because there is no return air in the upstairs, just one at the bottom of the stairs. The upstairs is small, its a 1 1/2 story and we leave the door open. I think if we decide to use the heat all the time we will add a return upstairs.

Brad White_185

Understood, Tim

My illustration was regarding "traditional" furnaces for, well, illustration. I agree and should have stipulated that condensing furnaces can and do operate differently and at lower temperatures.

On that last point, I advise anyone replacing a conventional furnace with a condensing furnace to increase ductwork and number of outlets to handle what is often 20 to 30 percent more airflow for a given BTUH output.

My essential point though is that either air or hydronic systems can be designed and operated well or poorly and one can exceed the other in comfort and economy.

ECM motors rock.

Thanks for making the points you did!

Brad

Steamhead (in transit)

You'll need that added return

more in the summer! If that 1-1/2-story is anything like the one I grew up in, unless the rafter and roof spaces are well ventilated from the soffits it will get real hot up there. Adding vents is, of course, cheaper than running A/C......

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Barry

Thanks for the reply. Our new furnace is a two stage which I think makes it more comfortable and may have a similiar effect as constant on. So far we can't really tell which system is on when we switch between the two.

mark ransley

I am suprised you did not get a second floor return installed, I dought you will be happy this summer as you wont cool upstairs. When I had AC installed I was told by many that without a second floor return it would not work, i had one put in. If no return was done I dought this guy did a load calculation in writing, I bet he just "guesed" on the BTU of your unit, this is wrong, oversizing heat leads to uneven heat, oversizing AC and it wont remove as much humidity. I suggest you get a second floor return put in. at least you have 2 stage heat, I hope all ductwork was sealed with take or mastic insulated ductwork is best.