Why is hot air better than hot water heat from a furnace

Frank_13

Is hot water heat more costly in oil usage and energy that hot air heat?

Ed Wallace_2

hot air vs hot water

no comparision hot water heat heats longer than scorched air only reason for scorched air is if you have central a/c

Pat Clark

forced air vs hot water

Actually, there is no difference in energy costs between comparable systems. Your house requires "x" btu's to replace the heat loss during cold weather. A forced air or hot water system rated at 80% would use the same energy to heat the space. This of course assumes the delivery system for each type of system (ducting for forced air & radiators for hot water) is engineered/designed correctly and installed correctly. Both systems can have problems and loss of efficiency if done incorrectly. What is important then is what are the comfort needs and preferences of the customer. This information is necessary to design the correct heating system based on those answers. A professional contractor should obtain this information and then can design the best system around those parameters. That system may be forced air, hot water, or a combination of both.

The Wall is primarily a hot water information goldmine. Lots of great people with a lot of knowledge to pass on. I know contractors who only install hot water and justifiably praise the benefits of those systems. Likewise I know contractors who only install forced air and justifiably praise the benefits of those systems. And then there are some, like myself, who see the benefits on both sides and praise each justifiably. Everyone's wants and needs for comfort are different and need to be addressed as such.

Have a great day. Sunny & 65 degrees here in Alaska today. Have you guys in the lower 48 hugged your Air Conditioner today?

Pat

sootmonkey

hey

What Pat said is true.

Josh M.

True however there is a big difference in radiant heat and hot air. Hot air is lost alot faster than radiant heat. For example every time you open the front door there is a huge exchange of air. Where as radiant heat only heats objects not the air. Not to mention in radiant floors lower temperatures feel warmer because it is heating your body where it needs it. Therefore is requires less BTUH.

Jackchips

Professionally

said, Pat.

chuck shaw

if you follow this link

http://www.burnham.com/pdfs/htghelper.pdf

and look in the PDF file, page 59 and 60 you may find some good information about the fuel consumption between hot air and hot water.

Chuck Shaw

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Steamhead

Comfort Issues

can also affect fuel consumption.

With a blown-air system, the moving air makes you feel cooler. This is great for a/c but not for heating. You end up raising the thermostat to compensate, which wastes fuel.

With a hot-water system, this is not a problem. I find that if I go from my house (with hot-water) to someone else's house that has scorched-air, it feels about five degrees cooler than my house even if the thermostat settings are the same.

Hot-water or steam works best for heating. If you must have a/c, a separate system designed especially for cooling works best.

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kf_2

Air versus Water

Pat,

At first glance that would appear to sound correct however, there are some other things that come into play here.

1) Warmer air is lighter than cooler air. What does this mean?

On average a typical warm air system delivers about 130 degree air into a space that is about 68-70 deg. Although this air blends with the room air, a large amount of it ends up at the ceiling, increasing the heat loss through the roof.

A hydronic system with 130 degree water running through baseboard does not create this kind of stratification from floor to ceiling. This is mainly due to the fact that it takes approximatley 230 times the space to move the same amount of BTU/hr by air as it does by water. This allows MUCH MORE AIR TO MIX WITH ROOM AIR.

2) Now lets take a look at that physical size difference I just mentioned (230 times larger).

Lets assume we have a 1" piece of pipe compared to a 10" x 18" duct, both equally insulated, both with 130 degree fluid temps, and both with equal surrounding air temps. The surface area of the warm air duct would allow about 10 times the heat loss of the 1" pipe. (This assumes that all the joints in the ductwork and insulation are completely sealed, VERY RARE)

3) A hydronic system does not affect room air pressure, a warm air system does.

A room under positive pressure can increase the movement of heated air out through cracks in the house. A room under a negative pressure can increase infiltration into the house.

When you mention efficiencies being equal I assume you were refering to published AFUE ratings which are actually just controlled combustion efficiencies. The things that I have mentioned here however, affect overall system efficiencies.

And by the way, when you do a Manual "J" heat loss calc, a 20% duct loss factor is added to the load for a warm air system. Only 7% is added to a hydronic system for pipe loss.
So the BTU/hr load of the same building will be HIGHER for warm air.


kf

Howard

so in other words

a building heated by forced air will require more BTUs per hour than if it were heated by radiant panels. That's not to mention the small 1/3 hp blower motor as opposed to the large 1/12 hp pump...

GW

ducts

There are many more bogus duct systems out there than bogus hot water systems, lots of energy can get lost due to high static pressure and leaky return ducts ( and supply for that matter)

So, BTU vs BTU is great, but the energy still has to be delivered to the rooms, and that's where the real fun starts.

All other comments are great

Gary

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Geno_11

verses

I agree with Gary, ductwork is extremely important. You have to look at the whole house. If your using warm air, how are you making domestic h/w? That would affect the outcome. The best I think is a combo system specifically designed for a given house with a small hi efficient boiler, radiant heat, indirect w/h, or maybe hydro air if you want a/c. There is no answer that adresses everyone. Each house and homeowner are different. The best systems aren't cheap. Like the man said," speed is just a question of money,... how fast do you want to go????

John@Reliable_4

According to Burnham's Heating Helper you will find that ...

with a heat loss of 100,000 btu's that hydronics will burn approx 2,448 gallons of oil. Now take the same heat loss with warn air and it jumps to 2,903 gallons a difference of 455 gallons more per year same heat loss. The average fuel savings is 18.6% for hydronic systems over warn air systems. John@Reliable