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Floor Furnace replacement?

Hudson Valley Carpenter's picture

The house where I'm currently living still has the original convection floor furnace.  It's a gas fired sheet metal unit, made in the early 1950's. 


It's had one major overhaul; new ignitor, valves and thermostat, about four years ago. 


It does a good job of heating the house but I'm wondering if there isn't a more efficient floor furnace made to replace this old guy. 

(post #115460, reply #1 of 12)

ooooh ... now there is something I've never thought about or heard of (i.e. replacing floor furnace w/ new). I've been in the energy business a LONG time (said at the obvious risk of revealing my age). I grew up standing over one of these every cold morning in my jammies.


Thinking out loud ... they are horribly inefficient by nature. Their distribution of heat is attrocious. Their combustion efficiency is in the toilet.


How about installing a hot water coil in the unit and eliminate the combustion part (don't forget to plug the flue). Heat the water w/ a boiler/water heater using efficient modern means ... may have to be to high temps (e.g. 160 deg+ maybe). Maybe also apply a fan to the coil for better convection/distribution efficiency.


Now you would retain the 'old world charm' (if they have any) of the floor furnace with the efficiency of 'modern' heating technology (although neither a coil or a fan is any newer than your '50s furnace).


Finding someone to install this? Maybe a tall order. Mr HVAC guy can you come install a floor heater that may get hotter than hell in my house? The liability may likely steer him way clear of you. Then ... technically you need a bldg permit to make the change ... and the BO may have something to say about it ... but not sure what. There are plenty of heating devices that get hot (e.g. steam radiators) w/ the potential human contact element. ... Food for thought, dude

There ain't NO free lunch. Not no how, not no where!

(post #115460, reply #3 of 12)

Didn't matter how inefficient they were, way back when natural gas was an unwelcome by-product of oil fields.  Any company who could put in a gas pipe line from the fields to a city could take all the gas they could handle, almost free, and resell it for pennies, at a good profit.


Most houses of this vintage here have been converted to central heat/air systems but those are even less efficient than the floor furnace and window air conditioners.


So I'm wondering if there isn't some kind of insulation retrofit for the sheet metal furnace, some way to gain significant efficiency, simply and economically.  


It seems to me that the worst heat loss is out the sides of the sheet metal box which is down in the crawl space, so wrapping the box with insulation or building a well insulated dog house around it might be a good remedy.  Whaddaya think? 


Another possibility is a mini-split system or systems, for both cooling and heating.  But I don't know if heating that way would be much more expensive than with gas or how efficient those units are as heaters.   What can you tell me about that idea?

(post #115460, reply #5 of 12)

Huhhhh?   combustion efficiency is in the toilet????      PROVE IT!      :)


 


Every atmospheric burner has a combustion efficiency of about 80%. 


 


However, system or AFUE efficiency is different.  Probably closer to a slop pail than a toilet.  LOL

(post #115460, reply #7 of 12)

However, system or AFUE efficiency is different.


This furnace, like most others of its kind in single story homes of this size (1250 sqft) is centrally located with one of it's registers in a hallway and the other in the big living room. 


As long as the interior doors are left open, convection works quite well to heat all rooms almost equally.  By not ducting heat through unconditioned spaces nor using a fan to move air, efficiency is gained effortlessly.


Efficiency has been greatly improved by adding insulation to the ceiling and installing insulated glass replacment windows throughout. 

(post #115460, reply #10 of 12)

I would guess the efficiency of those old floor furnaces was in the 60% range, if that.


Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

(post #115460, reply #12 of 12)

I would guess the efficiency of those old floor furnaces was in the 60% range, if that.


Wouldn't surprise me at all.  That's why I asked the original question. 


But the post to which you're responding is about comparative efficiency, not measured.

(post #115460, reply #9 of 12)

>>Every atmospheric burner has a combustion efficiency of about 80%.


I'm not sure where you got that figure, but I can assure you that me and my combustion analyzer disagree. (Although maybe I fell asleep in that part of my combustion analyst certification course....)







"Ask not what the world needs. Ask what makes you come alive... then go do it. Because what the world needs is people who have come alive."

Howard Thurman

======================================== "Man's capacity for justice makes democracy possible, but man's inclination to injustice makes democracy necessary." Reinhold Niebuhr: 'The Children of Light and the Children of Darkness' http://rjw-progressive.blogspot.com/ ========================================

(post #115460, reply #11 of 12)

Got one of those.  And a UEI/KaneMay and a brand new Testo.


I know what the good captain believes. And even he claims that analyzers lie.   BTW rumor has it he is about to retire.


 


If you measure just the combustion efficiency of a atmospheric burner, you will get about 80%.


Now, put a heat exchanger between the burner and the vent and everything changes. 


Change the combustion air temp and the numbers change.  Same with the exhaust temps.  Ditto with return air temps and cfm.


My point was the difference between combustion and system efficiency. 


I can make that floor furnace 100% efficient, even with 80% combustion.


Do I want to?

(post #115460, reply #2 of 12)

We still have floor furnaces around here too.

although probably 80-90% of the older homes have been updated to central heat and air.

I recently got an estimate of $4,500 to $5,500 to install central heat and air in a home which has a floor furnace and window air.

This includes the new ductwork

Good luck!

(post #115460, reply #4 of 12)

I recently got an estimate of $4,500 to $5,500 to install central heat and air in a home which has a floor furnace and window air.


That sounds like a very good price, by SoCal standards anyway.  But I seriously question the efficiency of those systems because the ductwork runs through unconditioned space, losing a lot of btus in the process. 


I've made quite a few improvement to this house to reduce energy comsumption, particularly electricity for AC.  It's now possible to maintain the inside temperature at 75 degrees or less, even on 100+ days, employing one 10K btu window AC unit.


My next door neighbor's house has none of the improvements I've made and uses more than ten times the electricity to cool his house with a central air system.


 

(post #115460, reply #8 of 12)

Reasonable price ... just make sure it DOESN'T include flex duct and that good duct sealant be used ... and insulate the duct if it is in unconditioned space.


Just say no to grey duct tape and flex duct. If his bid doesn't include rigid duct and mastic sealant agree to pay him ... say ... $400 more for the 'upgrade' (just a WAG).

There ain't NO free lunch. Not no how, not no where!

(post #115460, reply #6 of 12)

If the crawl space is deep enough it might be possible to replace the unit with a condensing forced-air furnace laying on its side. (Most condensing furnaces can lay sideways or upside down, as needed.) Then a few major ducts could be added to carry heat to far corners, without the need for a complete redo.


Conscience is the still, small voice which tells a candidate that what he is doing is likely to lose him votes. --Anonymous


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville