Natural gas wall furnaces
Hi there – I am curious if the GBA community has any opinions on direct-vented natural gas wall furnaces like the Rinnai EX22CN.
I have a 500 sqft kitchen + dining room + living room space with high ceilings and it’s currently heated by my massively oversized central air furnace that heats the whole first floor (60k Btu for a 1100 sqft downstairs.) The ductwork also runs through my unconditioned crawl and I’m pretty sure it loses a lot of heat on the way.
I was considering a mini-split with a high wall indoor unit but looking at the price of natural gas vs electricity here, and pieces like this https://www.greenbuildingadvisor.com/articles/dept/musings/ductless-minisplits-may-not-be-efficient-we-thought made me wonder if I could get the same benefits of a minisplit (downsizing, eliminating ducts, bringing the heat exchange inside the thermal envelope of the house) with the savings of natural gas.
Other considerations:
– I would like the unit to have a decent fan. Not sure why but I trust forced air movement more than passive convection. I have heard that the mini-split high-wall units do a nice job of this.
– I live in the Pacific NW so lack of cooling in the summer is a non-issue.
– Let’s assume that I can downsize or replace the existing furnace and continue to heat the other rooms in an alternative way.
– Ideally I would be able to find a 9k Btu gas unit that I could mount high on the wall to save floor space. In my 15min of googling though the Rinnai was about the best I could do.
– All the natural gas wall furnaces I found look pretty dated, which may be a sign…
Many thanks for any thoughts that people here have!
Max
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Replies
Just noticed that Rinnai does make an EX08CN and an EX11CN which would be much more appropriately sized. They still don't seem to be a good fit for a high wall mount, but maybe that's something I have to get over...
We love our Rinnai LPG heaters. First off, they are nothing like wall furnaces. They are Japanese design at its best. They modulate the amount of heat output and fan speed to match your conditions. Operation is whisper quiet and very cost efficient.
We have older models - an RHFE263 that is labeled 5700 BTU min - 11,000 BTU max, heats our 16'x24' office in CZ6. In the coldest windy weather it feels a little undersized, but it is pushing heat from the far end and competing with some very large windows in between. The same size heater in our dining room addition (about 10'x12') feels like too much heat. Our main heater, a 1004F. for the 1400 sq ft main house, is a 38K max BTU heater and does a great job. The layout contributes to air circulation. We also have a RHFE-556 which is over 20 years old. It is rated at 21,500 BTU max and heats our 16' x 18' great room room addition, again with lots of glass.
All this space is heated with less than 600 gallons of propane annually (includes hot water and cooktop). The heaters require little annual maintenance (clean the dust and dog hair out from behind them). And yes, it is a lot of heaters, but they are reasonably priced and allow us to run rooms we are passing through at a lower temperature than rooms we are occupying. And it gives us great redundancy, should one fail, which has never happened.
There is one point that I will fault Rinnai on in the older design, I am not sure if it is still true. They sense the temperature as the air is drawn into the back of them. This is not as accurate as a wall thermostat mounted to an inner house wall would be. Also the oldest, the 556, can only be set in 4 degree (F) increments - the newer ones are 2 degrees. All the controls are automatic so you cannot change the air flow rate, just raise the temperature.
And to respond to one of your last points, these are all mounted at floor level which I think is necessary for air circulation. All of ours are direct vent and the installs were very easy.
Max,
For environmentalists (people who read Green Building Advisor), the main disadvantage of heating with natural gas are the two ways that residential natural gas appliances contribute to global climate change: (1) The CO2 emissions that occur when the fuel is burned, and (2) the methane (natural gas) emissions associated with our country's leaky natural gas pipeline.
That said, gas-fired space heaters work well, and I suggested (in my November 2009 article, "Heating a Tight, Well-Insulated House") that they are one possible way to heat a well-insulated house.
Max,
I have a Rinnai unit in the home I am currently renting. It works well. The home I am building will have a mini-split. If I lived in the PNW then I would definitely opt for a mini split instead for two reasons:
1.) The PNW- especially WA- has some of the cleanest electricity in the country with all of your hydro plants. It would be a shame not to use it! Natural gas is cleaner than coal in theory but the pipelines are famously leaky. Methane is more potent than Co2 and remains in the atmosphere longer.
2.) Given the relatively steady temperatures in the PNW, your mini-split heat pump would be operating extremely efficiently nearly all the time. If the unit it sized properly then I cannot imagine that it would be much more expensive than a gas unit. (Remember too that the Rinnai unit with a blower uses some electricity so this must be taken into consideration.)
Got it. Thanks Rob, Martin, and Rick for the feedback!
Like any other heating problem, start by calculating the load. At a ratio of ~13BTU/hr per square foot of conditioned space even the EX08CN might be oversized for the load of 500' of conditioned space.
If natural gas is still the intended fuel, you can get both better heat distribution & higher comfort out of right-sized low-temp radiators or baseboards operating off a condensing water heater, as well as higher efficiency.
[Long-dormant thread but wanted to comment as the responses above have been marinating in my brain...]
Dana - thanks for challenging me to start by calculating the load. I haven’t got around to this project yet but when I do I will start with trying my hand at some of the good old Manual J software which I believe this site provides lots of guidance on. Shouldn’t be too far of a stretch for me to figure out.
Thanks also for recommending a hydronic solution. That could replace the whole furnace which would have the added benefit of freeing up most - if not all - of the floor space of my utility closet for conversion to a master bathroom!
Re: DIYing this... I recently installed an outdoor tankless unit for domestic hot water (Rheem model ECOH200XLN-1) and all of repiping I had to do in my crawl space - plus Dana’s advocacy of well designed hydronics - gave me an itch to try my hand at a radiant floor. I was thinking of picking up Modern Hydronic Heating: For Residential and Light Commercial Buildings by Siegenthaler. Has anybody else had success with that book, or other resources? Any opinions on whether a radiant floor is within the abilities of a reasonably handy but non-technical homeowner?
How about a nice wall mounted gas fireplace for heat and ambiance.