March 7, 2006

Energy-efficient water heating

Yesterday I made what I hope will be the last necessary major energy-efficiency improvement to my house for a while. A few years ago, I had the furnace replaced and the house insulated, but since the water heater still worked, I left it alone. Since then, the water heater's had problems, spraying water into the basement (faulty valve) and often running out of hot water quickly. I called Performance Systems Contracting to see if I could do solar hot water, but the house is too shaded, at least for now.

Since that won't work, I opted for an on-demand heater (which could eventually work with a solar heater). My old heater was a 40-gallon tank in my basement full of hot water that was kept at a constantly hot temperature, whether I needed to use it or not. My new heater is a smaller box that heats the water as it flows by.

Old 40-gallon water heater
Old 40-gallon water heater.

New on-demand water heater
New on-demand water heater.

I was a little shocked to see that the Energy Guide sticker on the old heater claimed an annual cost of $164 and the sticker on the new heater claimed $166, but then I looked more closely. The old heater was based on natural gas costing 60¢/therm, while the new one was based on 91¢.

Looking at my most recent gas bills, supply seems to be around $1.00, while supply plus delivery cranks that up to $1.75. The delivery number includes some charges that stay the same regardless of the gas I use, so it's not going to change to reflect usage as much. The new heater is listed at 187 therms/year, while the old one was at 272. As it's an on-demand heater and it's just me in the house. I hope to use even less than 187. (I don't know how they calculate estimated consumption.)

The installation was mostly smooth. Sediment in the old water heater blocked it from draining, so it was very heavy when Matt and Dave removed it. They knocked off the valve and 40 gallons of hot water poured down my driveway, a strange but largely unavoidable waste of energy. The new unit is much smaller, though packed with electronics, and it needed a new vent hole rather than using the chimney. (I now have two unused chimneys on the house.)

One thing that worries me: while both my furnace and water heater are much more efficient now, I've gone from units with pilots to units with electronic ignition. An extended power outage in winter is now a really big problem, sometihng I need to think about in the future.

If you'd like to see more of the heater and its installation, I've posted a gallery of photos, this time with some meaningful captions.

Posted by simon at March 7, 2006 7:58 AM in ,
Note on photos


Leo said:

Hello there,
Tell me... how is your experience with the Rinnai water heater so far? I'm looking into the business of renting these.
Thanks in advance

So far, it's been great. I really haven't noticed its being there, except for one time when I managed to flip the on-off switch in the basement by accident.

abase said:

I'm looking more to save space. Would you recommend this water heater for installation in the attic (i'm at sea level)? Thanks.