Are Tankless Water Heaters Really the Answer?

What’s not to like about tankless (also known as “on demand”) water heaters? They seem to have everything going for them, unlimited hot water when you need it and you’re not heating water when you don’t need it. They also tend to be highly efficient (92% and above) and take up less space than a conventional water heater. It’s no wonder that tankless water heaters have received high marks from green building advocates.   

I was therefore quite surprised to read the article “The Difference Between Storage and Tankless Water Heaters” (http://www2.buildinggreen.com/blogs/difference-between-storage-and-tankless-water-heaters)  on BuildingGreen.com with the subtitle “While they have higher efficiency, for most applications tankless water heaters don’t make sense”. This article was even written by the founder of BuildingGreen.com, Alex Wilson, a person whose opinions I follow and respect.

While I certainly agree with the article, I just want to point out a couple of local factors that make the article even more relevant for the Tahoe area where we build. Most of the residential construction that we do is for intermittent use, the homes are mostly second, seasonal, vacation homes. This use drives the hot water demand. A classic example is usage during the ski season. A family (maybe with guests) piles into a house (or condo) for the weekend. After skiing all day, everyone wants to take a shower. The water heater, which has been sitting idle for weeks (or months) is now under great demand. This should be a classic solution for a tankless water heater. What’s the problem? A tankless water heater should provide unlimited hot water allowing everyone to take a shower. As always, the devil is in the details.

A tankless water heater will provide endless hot water but at what volume? Tankless water heaters are rated by the gallons per minute (gpm) at a certain temperature rise (delta T). The temperature rise is the difference between the water entering the water heater and the temperature of the water exiting the water heater. The greater the temperature rise, the less flow comes out of the water heater. In other words, the more the water has to be heated, the slower the flow of hot water coming out of the unit. A large tankless unit might produce 8 gpm at a 45 degree temperature rise. Our local problem is the temperature rise. It is not uncommon to see the water coming into the house at 40 to 45 degrees especially in the winter. To get the water up to 120 degrees (a common water heater setting) means the temperature rise is 75 to 80 degrees. This reduces the output (gpm) of the water heater substantially. One person might be able to take a shower if no one else is using any hot water (dishwasher, washing hands, etc.). This is a very simple example and there are other variables at play but you get the idea.

Besides being cold, much of our water is very hard with dissolved minerals. Pretty much all the tankless manufacturers recommend cleaning and descaling the unit once a year to prevent mineral deposits from building up and reducing the efficiency. Once a year comes around pretty fast, a plumber will charge around $300-400 to do this.

Is all this effort worth it to eliminate the cost of heat loss from a conventional tank? How much does heat loss cost anyways? Thank god for the internet. A mathematician at the website leaningpinesoftware.com (http://www.leaningpinesoftware.com/hot_water_heater_tank_insul.shtml) has done both the calculations and testing to answer this question. I’m not going to go through the math or calculations here but using his numbers, I come up with heat loss cost of approximately $100 a year (again, many variables at play).

As much as I would love to love tankless water heaters, it is my opinion that we have local conditions that make them not the best option. Added to these local circumstances, they also have high initial installation costs added to the ongoing maintenance costs. Having said that, there some applications where a tankless unit would be the best option (a small condo or apartment for one or two people comes to mind).  Also tankless units are evolving and improving. We now have hybrid units, a tankless water heater with a small storage tank. Hmmm…

What is the best water heater strategy? It is my opinion that there are several options but no best universal solution. A couple of these options will include multiple conventional water heaters (both gas and electric). The best solution will be specific to the size of the house and its intended use.

Site drainage- not a problem until it’s a problem

A while ago, a potential client asked me if I could come by and look at a problem that showed up in her garage almost every spring. 

This is one of those very unfortunate problems that could have been easily prevented but is very difficult to fix. Obviously, in the springtime with the heavy snowmelt, ground water comes up between the garage footing and slab, soaking anything on the slab and wetting the bottom of the drywall. A functioning perimeter drain around the outside of the foundation may have prevented this but maybe not. The best way to prevent this is by removing the ground water from under the slab. The best way to accomplish this is with a drainage grid (some perforated pipe) under the slab. This drainage grid will gather any ground water before it reaches the bottom of the slab and direct it to either an outlet downhill or, if that is not available, to a sump pump. The drainage grid is neither difficult nor expensive to install. It just needs to be figured out during the excavation and foundation stages.

Site drainage is one of those things that nobody thinks about unless there is a problem. It can also be difficult to assess the probability of it being a problem. That is why, except for a couple of unique situations, I have put a drainage grid under every slab whether it be a garage or living space (especially living spaces) whether it is shown on the plans or not. I believe very strongly in Dr. Joe Lstiburek’s (buildingscience.com) statement that “You cannot build waterproof foundations; you can only build water managed foundations”.  

A perimeter drain can certainly help reduce the amount of water potentially flowing under a slab, but it may not be low enough. As an example, there is one house in our neighborhood that I pass by on frequent walks. Obviously groundwater is coming up between the foundation and slab. 

But- same day, same house with plenty of ground water present, there is no water coming out of the perimeter drain outlet. Hmmm… The perimeter drain is obviously not working in this example. OK, if it were working, would water still be percolating up in the garage? Maybe, maybe not. In my opinion, it’s a non-issue. Put the damn drain pipe under the slab, make sure it has a place to exit, and move on.

Underlying this whole drainage grid, perimeter drain discussion is the concept that these items be installed correctly, but that is a subject for another discussion.

As for the potential client with the wet garage? She decided that it was too expensive to retrofit the garage with proper drainage and she’s just going to have to live (unhappily) with it.

Building Contracts: Fixed Price or Cost Plus?

 

The contractual agreement between a builder and client can have a great impact on the success of the project. There are two general categories of contractual agreements for residential homebuilding and remodeling. One is the Fixed Price contract and the other is the Cost Plus (sometimes known as Time and Materials).

The Fixed Price contract is the easiest to understand and is usually the most straightforward i.e., I will build this house (deck, kitchen remodel, etc.) for X amount of dollars. The cost will only change if additions or modifications are made to the agreed upon scope of work. Also there are usually allowances in Fixed Price contracts for certain items that can raise the price if the allowance is exceeded. In theory, this type of contract usually limits the financial exposure of the client.

Attic Insulation

During a recent structural repair, caused by the record snows of 2010-11, we had an opportunity to not only upgrade the roof framing but also the attic insulation as well. This house was built in the early 1980’s and the roof system is a combination of open beam ceiling and attic.  The attic had two layers of R-19 fiberglass batts laid on the attic floor with many gaps and missing pieces. Some of the attic knee walls were not insulated and many of the ones that were, rodents had removed much of the insulation. Another issue needing attention was the numerous old recessed lighting fixtures that were not designed to have insulation near the fixture. These old fixtures essentially created uninsulated holes in the ceiling that allowed warm air to easily escape.