Water heating options...anyone tried condensing water heater?

Shawn,

I know nothing about condensing burners for water heaters.

As I'm sure you and I have written about before,,, I am a huge fan of Pre-heated solar,,, supplemented with demand. The newest generation of Tagaki/Rinnai/Paloma demand water heaters are great products. Yes the up front cost is significant,, but with tax credits they come in line pretty quickly. Venting issues are expensive if you have a long run of vent,, but they can be direct vented out a side wall if you have a place to do so.

My simple solar pre-heat system supplies ~70% of our hot water (for 2) on a year round basis. After about April 1 it does 100%. The takagi handles this perfectly,,, not caring what the inlet temp is.

There are other issues,, for example distance to fixture,, but these units are so small (even for a big out put) the idea of using more than one as a point of use is pretty attractive,, in lieu of a circ system,, at similar cost.

Icarus

PS My system is in far NW Washington state.

Icarus

 

Keep on posting Shawn. These topics are great!
Would you mind providing details why you think solar heat will only cover 50-70% of your use ? I think of that question as a cost/benefit, not a technical limitation. I am pricing out a system in the next few days, so know that increasing heating capacity is really only an extra collector cost; the plumbing, controller and pumps are a fixed cost.

Now, you may have to cover extra collector panels in the summer to prevent overheating, but I doubt that is a big deal to you given your obvious motivation to cut carbon emissions.

 

[ame=http://en.wikipedia.org/wiki/Geothermal_heat_pump]Geothermal heat pump - Wikipedia, the free encyclopedia[/ame]

If you had the room to do so, why not think about a slinky-coil geothermal system too.

 

Here in Manitoba, we have the cheapest power rates in Canada, among the cheapest power rates in North America. Cost-wise, an electric hot water tank is a good bet. Brand new homes are built with electric furnaces, if that's any indication of how our power rates compare to natural gas

I like natural gas water heaters strictly for their recovery rate. I really hate running out of hot water in the middle of a soak, and have never had that happen with a gas hot water tank.

In my home, I have a gas furnace, gas hot water tank, gas fireplace, gas heater in the attached garage. The stove and dryer are electric. FYI my gas bill just for heating hot water is $45 a month

I've never heard of condensing hot water heaters. They seem like a good bet. I've never seen them around here

 

It seems that the going rate for a condensing water heater is ~$2700 usd. A Takagi/Rinnai runs ~$800

The condensing unit runs ~95% ef,, the demand ~85%.

What I don't know is how much you can/should calculate in for standby loses. With a demand tankless standby is zero,, but there has to be some standby loss with a tank type. Lets just say it is 5% for the sake of argument. In that case $1900 for 5% advantage would be a pretty difficult pay off. Factor in longevity and I'm not sure it would ever pay off. (Understanding that not everything is about the payoff time!) A conventional tank with life expectancy of 10-15 years, a full stainless demand might last 15-30? I am still running a number of Palomas that are more than 20 years old.

For that $$ difference you could put 3 demand water heaters as needed at point of use heaters.

 

Keep in mind that depending on where your water heater is located, tank losses are not really losses during heating season.

Tom

 

Good point, Tom.

And if those incandescent light bulbs are only 5% efficient at producing light, doesn't that make them 95% efficient at producing heat?

 

Good point,,, but on an annualized basis,, they are still loses. Also perhaps not the most efficient way of heating space.

As for Hyo's point,, heating your house with light bulbs is not much worse than heating with resistance heating!

Icarus

 

I've heard that rabbits put out prodigious amounts of body heat, which can be particularly efficient if they're eating waste materials anyway. No idea how many it would take for a decent sized bunny-furnace, but you'd likely have too many well before next winter.

 

not if you eat some along the way.

 

You pretty much have to use 2x6 walls, but roof still only requires R-40. Almost everybody blows in R-50 or more, it's dumb not to when its so easy to do during contruction

No requirement for tri-panes, but most builders either use them or strongly encourage them. I have tri-panes with dual Argon fill and dual Low E. Compared to a dual pane, huge difference in comfort and performance

For electricity, fixed charge is $6.85 a month. First 900 kwh are 6.25 cents a kwh, balance is 6.30 cents a kwh

For natural gas, the fixed charge has now shot up to $13 a month. They have different tiers of consumption, in addition they calculate primary, supplemental, transportation, and distribution charges separately. Also despite the fact the meter reads cubic feet, the calculation is based on cubic metres.

If I did the conversion correctly, I think it works out to around $14 a decatherm. Still reasonable compared to other areas

 

Yeah I just *bet* you "heard" that ....

 

Screeching back to the OT, Manitoba Hydro is strongly encouraging new construction to use geothermal exchange heat pumps, with desuperheaters to assist hot water in winter, and primarily do hot water in summer

 

Air leakage accounts for the majority of heat migration through a building envelope

At one time, vapor barrier sheets were just overlapped and left like that. It was assumed air wouldn't migrate between the overlap, which was a huge error.

Now, minimum code up here requires Tuck Tape on all the seams, with acoustic sealant at the bottom plate. The rim board/joist needs a foam isolation pad as a thermal break.

One side effect of making new homes air tight is that indoor air quality has gone downhill. Depending on jurisdiction, a central exhaust system is now put in, and most builders will automatically do it anyway.

With the ducting already hooked up for central exhaust, going the extra step to a heat recovery ventilator is a no brainer. I run my HRV on low 24x7. I also do this to minimise radon exposure

Another side effect to air tight homes is radon exposure. It's not code yet, but some builders are venting the sump pump pit out the attic, same as for a sewer vent.

Here is how I would do a home, conventional stick frame 2x6 walls with a basement: use insulated concrete forms for the basement walls. You automatically have a thermal break, and an R40 wall, when done

For the exterior walls, use that BASF Walltite blown polyurethane insulation. You can achieve R values 40% higher than batt. Eg, a 2x6 batt insulated wall would normally be around R19, you can increase that to R26 with Walltite

Of course, all ceiling fixtures and exterior wall receptacles in airtight boxes, which are tuck taped to the vapor barrier

I think you're better off going out the side of the gable. Making sure you use duct insulation, with a slight downward pitch to the exterior hood. The downward pitch is to allow condensation to run out and away from the attic

In a climate like yours, venting out the roof can allow condensation to form in the vertical pipe. That condensation not only can freeze near the top, it will run back down into the fan

At least none that you can see at this point ....

Of course, they also operated as "not for profit" so only had to meet costs, not pay off shareholders and executives. Back in the late 1980's I briefly lived in a small town while doing a project. The town owned their own phone co, power co, etc

Phone service was $5 a month, plus long distance! Power was so reasonable, hardly anybody used natural gas. When I moved into the place, I went to the town hall to sign up for services. Then went for groceries, and when I got back half an hour later, the guy was patiently waiting for me to show up

Not many examples like that anymore. Locally, Manitoba Hydro appears to have jumped off a cliff. A new power dam up north will cost over 10 billion, but like a lot of Canadians, will then give away the power to the US at fire sale prices

They're also building the new office tower, with an estimated completion cost of $300 million. Oh, its LEEDs certified, whoop de doo.

Not sure why they needed a new office tower, the old building was fine. Does every lineman in Manitoba need an office suite now???

So mismanagement and abuse also happen in public sector enterprises too

 

In that case, make sure you put up that fanfold foamboard, then housewrap that is Tuck Taped at all the seams. Will make a big difference, especially on windy cold winter days

It's code here to have a 6 inch insulated duct from outside, to feed the utility room. An electric hot water tank needs no ventilation, and a condensing direct vent natural gas furnace is also ok with no vent.

A danger in making a house airtight without considering combustion air needs, is a tragedy in the making.

Good, you got off lucky. I've seen older houses where they vented the bathroom van into the attic, most of the rafters and roof plywood was rotten

I know you don't want to hear it, but I can't help myself:

S*** happens