What size water heater? How long will a shower last?

WHAT SIZE HOT WATER HEATER SHOULD I INSTALL? HOW LONG OF A SHOWER CAN I TAKE

Do a google search and if you don’t pull your hair out trying to get a simple answer then you are from another planet. This is terribly complex (for a non-engineer like me)  but I am going to make it simple by assuming many things for you.

The easy and conservative answer is this:

A 50 gallon gas DHW will allow two 10 +- minute shower at 110 deg F with a 2.5 gpm shower head (with my huge list of assumptions mentioned below). Depending on the recovery rate another person may have to wait at least 40 minutes  or so to take another 20 minute shower.  So what does that mean. It means take a 7 minute shower so you can do dishes, run a load of laundry and still take another shower an hour later. It means buy a 75 gallon if you have a couple of kids. It means buy a 100 gallon quick recovery (high BTU output) commercial DHW heater if you don’t want to plan and sequence usage or if you have a “thing” about long hot showers or never want to run out (also investigate on-demand/tankless heaters).

 Here is the partial  list of factors:

Inlet cold water temperature (avg)50 deg F (colder in Alaska, warmer at Equator)
Hot water heater (nat. or propane) temperature140 deg F (over that US code requires mix valve)
Hot water heater size (adjust with the formula)50 gallon (189 liters)
Distance of furthest showerLess than 50 ft
Draw Down (30 deg temp drop)70 % or 35+- gallons on a 50 gal tank
Shower head rating2.5 gpm (use 3.5 if you remove flow constrictor)
Temperature of a hot shower (min)110 deg F at the head (cools quickly as it leaves)
Ratio of Hot to Cold water (see formula)Approx. 70% hot 30% cold
First hour rating (FHR)Approx. 50 gallons
We are ignoring mixing valve calcsToo complicated for me, too many variables.

Caveats:

  1. A couple (2) can use a 40 gallon heater by adjusting use pattern but a family of 4 will have trouble so if you have a 40 I will just say it is undersized (don’t argue).
  2. If you take more than a 10 minute shower I hope you are doing it for therapeutic reasons. If you keep your 2.5 water saving shower heads (I hate em…!) then you get a 14 min shower. I take a small drill bit to my 2.5 heads to increase the flow. Do I feel bad…? NO!
  3. Quick recovery DHW heaters and boilers for floor heat connected to domestic hot water change everything. The BTU input can shorten recovery time considerably.
  4. On-demand heaters change everything. This information is for gas heater with a storage tank. Do not get a 11 liter per minute on demand heater and expect to take long showers while any other appliances are being used (dishwasher, clothes washer etc). On demand heaters are great energy savers but get a good plumber so you don’t have sudden “cold plugs” and insure you have the flow rate and pressure needed. Low flow shower heads are notorious for causing cold surges as the heater shuts down (happens more when pipe size and pressure add to the problem). Adding a pressure pump and expansion tank are probably required equipment.
  5. If you live in a warmer climate with mild winters, you will have quicker recovery and a better FHR.

Skip the Algebra if it isn’t your thing……Formula: X is gpm hot, Y is gpm cold, 140 deg F hot, 50 deg F cold. 110 deg F is desired “hot shower” temp. If you like it scalding then you will have a few minutes less of hot shower. Just increase the 110 deg F desired temp. This is the “Ratio Formula” for hot to cold.

140 X + 50 Y = 110 (X+Y)  Hot and Cold in, 110 hot shower out.

140X-110X+50Y-110Y=0

30X-60Y=0 or 30X=60Y so……X=2Y  

You need twice the hot as cold to maintain the 110 deg F. (I know, it sounds wrong, other sources often say a shower uses 70% hot to 30% cold). So we are close to the 2 to 1 ratio. Without an assumed ratio you cannot calculate but you can get a bucket and measure how many gallons at a given temperature (use a gauge) you get before the “draw down” drops you to below your desired shower temperature.

So using slightly conservative numbers,  a 50 gallon hot water heater will give you 34+ gallons of hot water. Add another 16+ gallons of cold (ratio above) to the approx.. 34 gallons of hot water to get about 50 gallons of shower water at 110 deg F.  50 divided by 2.5 gpm gives you a 20 minute shower (or 2 @ 10 minutes). I think this number is the best you can expect from a 50. With mineral build up, higher gpm because you drilled the flow constrictor, slower FHR and seasonal changes you will be closer to 14-15 minute shower max.

If you like it really hot hot, reduce to 14 (2 @ 7) minutes. If you can reduce to 10 minutes then you can get 4 people showered by waiting 40-60 minutes after the first 2 showers. All bets are off if you wash dishes or clothes during shower time.

Good luck and don’t hassle me over my assumption and bad math. Just send me the better math formulas or make your case for longer shower numbers. Better yet, just say the size you like for a couple, family of 4, etc living in say Santa Fe, NM or San Miguel de Allende, Mexico (cold winters, warm summers).

Ron Smith (cranky ex-general contractor).

Should I Test My Home For EMFs (electromagnetic fields)?

ELF and EMF radiation at high levels have been shown to have negative health impacts. They can lower melatonin levels and there are also studies of milk production from cows that show their production decreases with Elf/Emf radiation (they sometimes graze under high tension powerlines).

A T.V. in the old days had an emf burst when you turned it on (remotes are great for keeping your distance) but now the readings are just a few milligauss (mg) depending on your TV. Still….keep yourself and kids back from the large sources like microwaves and electrical transformers.

Powerlines and larger sources of EMF: For long term constant exposure, Sweden has a 1mg (milligauss) limit and Florida, USA has a 250mg limit. High tension power lines are usually around 345,000 watts and produce measureable emf’s which drop as you move out from under the power lines or away from a 25kva or 50kva transformer (commonly on the CFE street poles in San Miguel).

Do you need to test? If you suspect a source such as a transformer on a pole outside your house then yes, I recommend testing. Or download an app for android or I phones. They don’t compare well in my tests to my F.W Bell meter but at least they can indicate if a field exists then you can test further with better equipment. SMA Home inspections uses an F.W. Bell ELF meter that measures the emf in milligauss (mg). (Note: 1 microtesla=10 milligauss). Measurements of appliances up close can give 20-60 mg and a microwave might be around 200-300 mg. The field drops rapidly as you move the meter away hence distance from the emf source will lower exposure for those concerned.

Exterior Tile and Concrete Sealers

You want a penetrating sealer made with siloxane/silanes. I like Sika products, use Sikaguard 70 if you can find it here at Home Depot mexico. At between $2,000 mxn and $3000 mxn for 19 liters it’s not cheap but you can spend more for the product I use, Imperquimia Aquasil Life Style which costs $6800 mxn for 19 liters. But the coverage is much better than SikaGuard and you only need one coat.

They are not acrylics and do not form a seal at the top of the tile. They breathe and penetrate concrete, tile and other porous masonry surfaces without changing the look of the material. Any top coat sealer will degrade in the sun. Read the review at the link here and then begin your search with your tradesman to find the product locally. If you have a failing finish on your tile it has to be stripped to get the porosity back so the penetrating sealer can get in as deep as possible. Just sprinkle water on the surface and if it does not absorb and turn dark you have to strip or wait to seal with a penetrating sealer.

Watch out for waterbased formulas with silicone. I am not a fan yet of these hybrids that have acrylic mixed with some silicone but I think Okon S40 is a good product if you can find it here. I generally prefer oil or solvent based penetrating sealers although there are some waterbase siloxane/silanes that pentrate and perform well. Home depot carries Thompson’s Waterseal Multi-surface but their website and info at Home Depot is lacking information about what it is in it and the reviews by users are horrible. They lowered the VOC’s (volatile organic compounds) probably to meet California standards and made it thicker and stickier and it creates a mess on your concrete/masonry surfaces. Always do a small test patch first.

Go to Services and then Subcontrator Referrals on this website to find several tile refinishers that you can contact. Stay away if they do not recommend a penetration sealer for the exterior.

Is Radon a Problem in Mexico?

Recent discussions on the SMA Civil List about radon in the water reminded me that I wanted to post a little information and resources to more information about Radon here. I may start testing for radon within the next year as an “add on” service like the mold testing and inspections we do but so far the data doesn’t show a high risk in most mexican cities (see below).

Radon is being studied in Mexico and there are also global radon maps. Here is a link to a study: https://www.researchgate.net/publication/223704481_Distribution_of_indoor_radon_levels_in_Mexico
There is a table with Radon levels of nearby cities of Celaya, Guanajuato, Queretaro etc. Divide by 37 to get the pCi/l so you can compare to the EPA recommendations here: https://www.epa.gov/sites/production/files/2015-05/documents/hmbuygud.pdf Anything below 2.3 pCi/l is considered low risk but above 4.0 pCi/L you should consider mitigation to reduce the levels.

Note that geology changes and radon levels will defer from area to area. So if anyone has information on radon testing in San Miguel de Allende I would appreciate the link. There is also a study of radon in water at a thermal water spa if you want to google that.

Solving Hard Water Ecologically

TAC or “template assisted crystillaztion” is a newer technology finally gaining ground in the United States and I am looking for a source here in Mexico. It does not need to be backwashed and does not put salt into the sewer like the traditional softeners with brine tanks. So help me out if you find a source for TAC. TAC originated in Germany and was tested by Arizona State University in April 2011. The link below is to a .pdf file with a power point presentation of the testing structure and the results of several technologies. TAC came out on top for the lowest scale deposits on a hot water heater coil. Also below a link to a nice explanation of TAC.

Hot water heaters pay the biggest price from scale build up but we all know it is the clogged shower heads and the plugged up low pressure on the sink faucets that annoy us the most.

Low Cost Alternatives: take off any shower heads and aerators (those little screens screwed into the spout of your faucets) and soak in vinegar overnight. Scrub with a brush and replace. You can tie a plastic bag with vinegar on the faucets and the shower heads you cannot remove. Wrap a rubber band around the bag to seal it and get some of the fixture soaking in the vinegar. Remove the next day (or wait 2 or more days if you can) and scrub with a plastic brush.

Here is a link about TAC, a nice explanation: https://www.e-tankless.com/how-TAC-works.php
Here is the study from ASU: https://static1.squarespace.com/static/56251170e4b095e786b34523/t/565ddd7ae4b0d522090423ba/1448992122459/AlternativesIonExchangeSofteners_April2011.pdf

10 Things You Should Know About Mold

I just finished another mold test in La Lejona II here in San Miguel de Allende, Gto. Mexico. Many sources of mold were found and I advised the owners to spend the test money on controlling moisture in their house but when you are suffering from allergy symptoms sometimes you just need to know. So we tested for stachybotrys (black mold) and aspergillus and penecillum and the tests were negative for both. That did not mean they did not have mold, they did. It just means the worst ones for your health were not present. So that allowed them to focus on the moisture control tasks ahead and continue their search for other possible allergins. The EPA has been weakened by the Trump administration but I am glad they got to do some research on mold and provide us with information on their website (link below). Also, do your own mold clean up with these 2 links from the CDC and EPA https://www.cdc.gov/mold/cleanup.htm https://www.cdc.gov/mold/pdfs/BLEACH_USE-fs-P.pdf

Ten Things You Should Know about Mold (from the Environmental Protection Agency)

  1. Potential health effects and symptoms associated with mold exposures include allergic reactions, asthma and other respiratory complaints.
  2. There is no practical way to eliminate all mold and mold spores in the indoor environment; the way to control indoor mold growth is to control moisture.
    If mold is a problem in your home or school, you must clean up the mold and eliminate sources of moisture.
  3. Fix the source of the water problem or leak to prevent mold growth.
  4. Reduce indoor humidity (to 30-60%) to decrease mold growth by:
    • Venting bathrooms, dryers and other moisture-generating sources to the outside
    • Using air conditioners and de-humidifiers
    • Increasing ventilation
    • Using exhaust fans whenever cooking, dishwashing and cleaning
  5. Clean and dry any damp or wet building materials and furnishings within 24-48 hours to prevent mold growth.
  6. Clean mold off hard surfaces with water and detergent, and dry completely. Absorbent materials such as ceiling tiles, that are moldy, may need to be replaced.
  7. Prevent condensation: Reduce the potential for condensation on cold surfaces (i.e., windows, piping, exterior walls, roof, or floors) by adding insulation.
  8. In areas where there is a perpetual moisture problem, do not install carpeting (i.e., by drinking fountains, by classroom sinks, or on concrete floors with leaks or frequent condensation).
  9. Molds can be found almost anywhere; they can grow on virtually any substance, providing moisture is present.
  10. There are molds that can grow on wood, paper, carpet, and foods.

https://www.epa.gov/mold/ten-things-you-should-know-about-mold

Does magnetic treatment of hard water reduce scale deposits?

There is no consistent independent testing that supports the claim. There are many studies that show that magnets and magnetic fields have no effect and the few that show a reduction in scale build-up are often flawed or biased or have specific industrial applications. For the average home owner I think you should spend your money on a traditional water softener with a brine tank. The dissolved sodium chloride is minor. The excerpt below is from this article here.

Consumer Reports magazine (Denver 1996) tested a $535 magnetic water treatment device from Descal-A-Matic Corporation. Two electric water heaters were installed in the home of one of the Consumer Reports staffers. The hard water (200 ppm) entering one of the heaters was first passed through the magnetic treatment device. The second water heater received untreated water. The water heaters were cut open after more than two years and after more than 10,000 gallons of water were heated by each heater. The tanks were found to contain the same quantity and texture of scale. Consumer Reports concluded that the Descal-A-Matic unit was ineffective.

Mold: Bed Bath Recalls UGG Comforters

Bed Bath and Beyond has recalled around 175,000 comforters because of mold contamination. This time of year, many of us here in San Miguel de Allende are huddled around space heaters (see previous blogs on air quality issues) and dive into bed early to keep warm. If you brought a comforter from the U.S. and wonder if it safe you can go here for more information on the recall. I am not an alarmist. If you keep your comforter clean and dry there should not be a problem with mold. But if you have one of these comforters I suggest getting the refund and start with a mold-free comforter.

I received this notice from IAQA, my Indoor Air Quality Association membership:

“Bed Bath & Beyond Recalls Nearly 200K Comforters Over Mold”
Good Housekeeping
Bed Bath & Beyond is recalling nearly 200,000 UGG comforters sold in stores nationwide and online over concerns about mold, and warns anyone who bought the products should immediately stop using them.”

SMA Home Inspections does basic mold testing and can make suggestions on how to minimize mold growth in you home.

Is It Safe To Heat Your Home With The Gas Oven?

If you research this you will find the answer to be a resounding NO…!!! THEY COULD BE WRONG and here is why. If it is dangerous and if you will get carbon monoxide (the most often cited danger) then you better forget cooking the turkey for thanksgiving. Why is turning on your oven for 3-5 hours to cook a turkey okay and turning on your empty oven for an hour or two to warm up your kitchen (and dining and living room in today’s open design homes) not okay?

First of all, many vent less gas log sets found all over the world and very common here in San Miguel de Allende  burn less efficient on purpose. Some have a yellow flame like a real fire which may indicate lower temperatures and incomplete combustion. Your oven should have a blue flame which means it is more efficient than many of the alternative space heaters using propane or natural gas including vent less gas log sets. Ovens are built to bake bread, cook a turkey and keep food warm for hours and hours at a time. They are usually not vented, poorly insulated and let all of the heat into the room which makes for a decent source of heat. If there is carbon monoxide it should be well within standard limits, otherwise they could not sell you the oven for cooking.

The only real danger is if the oven flame somehow goes out while the valve/knob is left on and at the same time the safety malfunctions and sends unburned gas into the house. Does this happen when you are cooking a turkey? Note: newer gas log sets have an oxygen sensor that turns off the gas if the room becomes depleted of oxygen below a certain safe level. Does your gas heater have this safety feature? Your oven does not have this feature so be careful using you oven as a space heater.

Yes it is true, an oven was not made for space heating. But the blue flame of my oven tells me it is burning more efficiently than my gas fireplace log set. After an hour or so my eyes are burning from the fireplace log set. This is not the case with the oven. Distribution is a problem equal to both heaters. So I don’t recommend using an oven to heat a large area. But if your oven is safe to cook a turkey for a few hours, then it is safe to turn on with or without a turkey to take the cold edge off the kitchen in the early morning (never leave an unvented gas heater on while you sleep). Am I missing something here?

Are Propane Gas Log Heaters Safe?

Propane gas log sets come in a variety of styles and sizes. They are generally safe to operate but only for an hour or less at a time. The Canadian study here  found that 1 in 5 homes using vent less heaters like the gas log sets found in many San Miguel homes had unsafe levels of carbon monoxide (CO) and oxides of nitrogen dioxide (NO2).  Your log set is probably located in a fireplace nicho, but don’t let that fool you. Look inside and up and you most likely will find there is no vent or chimney. You have a vent less heater and you need to be careful.

Personally, I find them unhealthy and I hope to see more homes with direct vent heaters, radiant in-floor heat and other safer and healthier heaters installed in San Miguel homes.  Gas log sets are designed to burn less efficiently with a yellow flame (like a real fire) instead of the more efficient blue flame. Fortunately, the doors and windows in many San Miguel homes leak air and this allows for contaminated air to exit and cleaner air to enter. But of course this lowers the efficiency of your heaters.

What are the warning signs:

  • yellow/orange flame instead of blue/white indicate less complete combustion
  • strong smell of combustion
  • physical symptoms of incomplete combustion (eyes burning, headaches, nausea, dizziness etc)

What can you do ?

  • install carbon monoxide sensors that sound an alarm
  • purchase good quality gas heaters,
  • service the gas heater every year in the fall and insure you have blue flames indicating more complete combustion of the propane gas
  • do not use your heaters continuously, use them for an hour at most and supplement with electric heaters, warm clothes, electric blankets etc.
  • open you doors and window when the outside temperature is higher than in your house. Close up in the late afternoon when you feel the cool air outside.