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-   -   Space heating: warmer house and fewer $$$ (http://www.diychatroom.com/f17/space-heating-warmer-house-fewer-17017/)

pcampbell 02-13-2008 06:33 AM

Direct vent room furnace: warmer house and fewer $$$
 
We recently got a Rinnai direct vented space heater and if I were allowed (by my wife), I would heat the entire house this way.

While the AFUE numbers are nothing amazing at 84% for natural gas (closer to 87%+ for kero or #2), the difference is that 100% of that 84% goes into the room you are trying to heat. With ducts, I would venture to guess you are looking at a minimum of an additional 15% loss, if not more. So an 84% furnace would really be more like 72% when the heat actually reaches you.

Furthermore assuming you have multiple heaters, now you have zoned heating, and can shut off the heat in areas not used. You could turn it down to 60 in other rooms when you sleep, and do the same to the bedroom during the day. A properly sized heater heats a room up literally within minutes, and they are programmable as well so can already be warm when you wake up.

Last month with the central furnace, we used 10 million BTUs. Our house is only 750 sq. ft. With the space heaters I could easily see us using 3/4 or even 1/2 that with space heat, AND being warmer.

Of course it all depends on YOUR house and your living style. I was surprised to find very little about Rinnai or direct vent space heaters in searching the forums. Apparently they are very popular in very cold climates, Alaska, Canada, Maine, etc.

redline 02-14-2008 02:39 PM

How old is the central furnace?

pcampbell 02-14-2008 03:04 PM

I am speaking generally but ours is just a few years old Trane XR80 80% AFUE. I don't think a 96% furnace could even compete.

redline 02-15-2008 06:04 AM

Quote:

Originally Posted by pcampbell (Post 97557)
... With ducts, I would venture to guess you are looking at a minimum of an additional 15% loss, if not more.

Are the ducts properly sealed and insulated?

What is the btu of the Rinnai?

pcampbell 02-15-2008 06:43 AM

Redline, I do not have a laser thermometer, but I would be really curious to test exiting temperatures out of the furnace and then out of the registers. Doing some web research, 15% loss is considered normal/good for sealed and insulated. That's according to EERE.

I have some problems with our system that we're working on, but that is a different story. I was diagnosing problems and realized there were some very poor seals at duct junctions. When I thought I was finished I found an even bigger leak, huge, right at where the furnace meets the A/C, just whooshing out hot air. Working on that as well.

BUT, I mean to say that I believe even a perfectly installed 96% central system could not compete with multiple 84% direct vent space heaters ;) At least in terms of efficiency. A perfect 96% system with very minimal losses would be close... but, for many not realistic. A further advantage is that the Rinnai's are basically maintenance free, and if I can install it, anyone can!

Our Rinnai is 21500 BTU. It is not big enough to heat the entire house from a single location. Even if it did this creates hot rooms which is no fun. It has a hard time keeping the room which is furthest from the heater above 65 (which also has 3 outside walls and 4 windows and a front door with no storm door). Surprisingly we saw the roughly same results in 32 and single digit temperatures (a good test!). I think if we had gotten the 38000 BTU model it would. But most efficient and most comfortable would be smaller units in multiple locations.

Bondo 02-15-2008 06:31 PM

Ayuh,...

I'd think that by the time you bought multipule space heaters,....Plumbed fuel to them, along with venting,+ everything else,.....

I'd rather have a well planned out Central system.......

wfischer 02-15-2008 09:21 PM

Quote:

Originally Posted by pcampbell (Post 97557)
Apparently they are very popular in very cold climates, Alaska, Canada, Maine, etc.

Um, actually, everyone around here uses either kerosene-burning furnaces or boilers, or pellet stoves, or monitor heaters, or wood-burning furnaces.

BleachCola 02-16-2008 01:56 AM

do you have a link to these heaters? I just had forced air installed on my first floor and I need a easier solution for the 2nd floor, its about 700sq ft

thanks

pcampbell 02-16-2008 06:24 AM

wfischer, are you disagreeing with me? I said they are very popular in cold climates and you continued to say yes people use "Monitor" heaters among other things.

BleachCola, Check out http://www.alsheating.com/
But I'll warn you his page is a little confusing.

For oil check out: http://www.toyotomiusa.com/
For gas: http://www.rinnai.us

There is also Monitor (yes that is the brand name), but I've heard better things about Toyo/Rinnai and Al (above) will say the same thing.

The heaters are $900-$1300 for gas. Not sure about kero. Gas here is cheap. Running gas and venting is easy. The vent goes straight out (horizontally) with a 3" hole in the wall. For gas CSST (orange flex tube) is not cheaper, but so much easier :)

http://xj.cdevco.net/heat/exhaustintake.jpg

redline 02-18-2008 04:19 PM

Quote:

Originally Posted by pcampbell (Post 98402)
... Gas here is cheap.



How much is natural gas in your area?

How much is electricity in your area?

pcampbell 02-19-2008 06:03 AM

Natural gas is $1.45 per therm delivered. I consider this cheap, considering oil is $3.39 for only 25,000 or so more per BTU. The only thing feasibly cheaper to heat the house is wood. Electricity is 0.15 KW/H.

CowboyAndy 02-19-2008 06:32 AM

Quote:

Originally Posted by pcampbell (Post 98402)
wfischer, are you disagreeing with me? I said they are very popular in cold climates and you continued to say yes people use "Monitor" heaters among other things.

BleachCola, Check out http://www.alsheating.com/
But I'll warn you his page is a little confusing.

For oil check out: http://www.toyotomiusa.com/
For gas: http://www.rinnai.us

There is also Monitor (yes that is the brand name), but I've heard better things about Toyo/Rinnai and Al (above) will say the same thing.

The heaters are $900-$1300 for gas. Not sure about kero. Gas here is cheap. Running gas and venting is easy. The vent goes straight out (horizontally) with a 3" hole in the wall. For gas CSST (orange flex tube) is not cheaper, but so much easier :)

http://xj.cdevco.net/heat/exhaustintake.jpg

These are very popular where I live, but more so with the kerosene ones. Natural gas is non existant here, and most people have never heard of LP. I see a few houses with LP tanks, but the majority here is kero or #2 oil.The "monitor" heaters are incredibly efficiant, but you have to have an open floor plan for them to heat the house evenly. My father in law has them in his house (built last year) 1500 sq ft raised ranch with 1 large unit in the living room, pointing down the hall. It heats the kitchen and living room pretty good. There is another smaller one in the master bedroom that points toward the door across the hall to 2 other bedrooms. Lastly, there is one more in the basement.He went through 300 gallons of kero last year, and is running about the same this year.Personally, I don't like them as the far side of the room is colder than the area directly around the unit.

redline 02-21-2008 04:17 PM

Quote:

Originally Posted by pcampbell (Post 97557)

While the AFUE numbers are nothing amazing at 84% for natural gas (closer to 87%+ for kero or #2), the difference is that 100% of that 84% goes into the room you are trying to heat. With ducts, I would venture to guess you are looking at a minimum of an additional 15% loss, if not more. So an 84% furnace would really be more like 72% when the heat actually reaches you.

Our house is only 750 sq. ft. With the space heaters I could easily see us using 3/4 or even 1/2 that with space heat, AND being warmer.

How do you figure that you will use 3/4 or 1/2 less?

What is the square footage of the room that the Rinnai is in?

pcampbell 02-21-2008 04:59 PM

84% on a space heater is actual heat delivered. I did not say the single Rinnai could do this. Our house doesn't have the layout to allow it. We'd need 3 of them.

Even a 96% furnace is not 84% actual heat delivered unless you believe you can achieve only 12% loss in duct work which is a very ideal circumstance.

An 80% furnace with 20% duct loss is 64% ACTUAL heat delivered.

So if the 80% uses 10 million BTU to deliver 6.4 million BTU to the house, the 84% space heater only needs to burn 7.6 million to deliver the same amount of heat. That is 3/4 of the energy there.

LawnGuyLandSparky 02-21-2008 09:23 PM

Depends on where your ductwork is. If you "lost" heat in a duct, where do you think it went?


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