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Zooomer 07-13-18 01:41 PM

Need some help conceptualizing a reduced cost water heater solution for rentals
Backstory, I own rental properties and want to come up with a water heater solution.

1. Cost of city permits
2. Cost of electricity (18 cents) in some of my areas (MI)
3. Cost of equipment and installation
4. Maintenance

Gas power vent is expensive and requires multiple permits. The powervents seem to go bad often.

Resistive electric is cheap to install/maintain but costly to run.

Hybrid is expensive to buy, requires maintenance (dust), cools houses in winter.

I need something scalable and inexpensive so I was thinking of a preheater tank (non insulated). Not sure if it would condensate too much. Then an electric resistive. Preheater wouldn't add to permitting. I thought maybe a DC element in it connected to a single solar panel. Eliminate the inverter and being low voltage the wiring requirements would be low. This solution could also be combined with an electric hybrid if the situation merited. Still, feels like someone could come up with something better.

Edit to add: I also thought of feeding the water heater through a coil in the furnace and a flow switch would trigger the fan. This would be efficient in winter with a 90% and cool the air while warming water in summer (at little cost).


Elcam84 07-14-18 07:12 AM

Im surprised that a land lord would be this worried about his tenants electricity bills. Thats almost unheard of.

As for the gas water heaters with the power vents I have heard the same from the plumber that does the commercial jobs. He said that he has replaced many with conventional gas water heaters because of fan control failures. The small energy savings doesn't cover what it costs in repairs and down time. He also swaps out more tankless heaters with tank type than he installs due to similar control board issues.

Conventional gas water heaters are quite efficient compared to electric. Usually a under half the operating cost or less.

I like the hybrid units but their recovery time is very slow in just heat pump mode and in a rental it'll be running in regular electric mode to try and keep up. I dont see a cost savings there.
As for the cooling its a good thing here... They also dehumidify which is good here year round as its humid even when its below freezing here... Great if its in the house or garage here. (most are in the garage here)

Using a solar panel and tank for a preheater isnt economical. The cost of the system and the cost of the panels will take a very long time to pay for itself and even longer in Michigan where you are well out of the good latitudes for sun and have allot of overcast and cloudy days.

I would just go with gas waterheaters and call it good. You may be able to cut some operating cost with tankless but it all depends on the usage patterns. IE if they take baths you will need a larger unit. Bath tubs waste allot of water and energy and LOML always has to have that big jaccuzi tub...

Zooomer 07-16-18 02:00 PM

The standard gas water heater doesn't solve the issues.

-They cost more than electric (not a big deal)
-You have to vent through a chimney using a chimney liner. This adds additional cost, creates a failure point in the roof, adds permitting costs. I like to eliminate holes in the roof and chimneys as these are old houses and I've had leaks and several $1k+ costs to repair old chimneys.

Looking into solar, it's not a solution in MI. Way too little exposure year round.

I'm exploring 2 solutions now:
-Heat exchanger in the plenum above the furnace.
-Heat recovery system in (shower) drain water.

Elcam84 07-16-18 04:13 PM

The heat recovery from the drains will involve allot of custom manufactured parts and allot of labor to install for an unknown amount of heat recovery.

The furnace idea can be done but a heat exchanger in the furnace will reduce airflow quite a bit and also increase furnace run times as some of the heat is now being sapped into the water exchanger and then reducing airflow also effects comfort in the house.

Both of those pose allot more issues of install and down the road than a hole in the roof for a flue pipe.

Gas waterheaters are $100ish more than electric but they also need a flue pipe and gas run to them if you don't have it there. But the operating cost of gas is far far lower than electric and you will recover the install costs pretty quickly.
If its on an outside wall you can run the exhaust out the wall in many cases. More common up north as most houses there are sided instead of bricked and if you have a basement its even easier.

In your application a standard electric unit would be the easiest solution and a gas unit would be the most efficient. If water usage isn't that great then a gas tankless would work if on an exterior wall or use a condensing version that uses PVC venting.

IMO the non condensing versions arent worth buying unless its outside or on an outside wall as the venting flue pipe is cost prohibitive.

Zooomer 07-16-18 04:44 PM

Thanks for the reply.

I have many rentals and I've gone over solutions and dealt with problems for a decade.

Over the weekend I had DTE change a gas meter, when they turned the gas back on, the water heater didn't turn back on. (70% gas style). So I log this as an issue. Rare, but still a potential fail point.

The idea is to reduce maintenance and failure of all kinds. Rentals are really a numbers game so it's a math equation at some point.

When rehabbing an old house, I have never been able to vent outside along the side of the house unless it had a side mounted chimney. Installation costs and permitting is high on a gas unit. They make you do a leak down test for 24 hours and charge you additional $ if you disturb the gas line.

Almost all landlords and many new constructions are going with resistive electric because the install and purchase price are much lower, plus you don't have a vent issue. The only real downside is higher cost to tenant and unfortunately most landlords are too short sighted to care. Not to mention tenants don't shop based on that because they don't know.

If you have a system of any sort that includes a passive storage you can raise the temp of water in the winter ~25 deg and summer 10-15. Assuming a hot water tank at 125 you'll increase hot capacity and reduce any bill by up to 30%. Totally passively with zero maintenance and low cost.
Typical electric costs about $50/month, gas 1/3 of that (depending on use of course).
You could combine passive storage with another solution.

An AC coil is far more restrictive than what I'm proposing and doesn't cause issue so restricted airflow is not a consideration. A new furnace heats at 96% efficiency so 'preheating' the water is going to be more cost effective than any solution out there. Should be no maintenance either. Just have to decide whether to run the fan or just let it happen.

Rentals is a side business for me. Primary business has manufacturing setup so I would run any idea at scale. Either in house or with an existing partner.

---15 years ago I built a crude heat recovery unit for my shower. I got 10 deg rise in about 30". Was a poor design. Since them I've considered a double wall cast P trap with recovery built in. Kind of more of a new construction thing tho.

NiHaoMike 07-17-18 04:29 PM

Design a low cost heat pump water heater based on modified window A/Cs?

Zooomer 07-18-18 11:12 AM


Originally Posted by NiHaoMike (Post 59520)
Design a low cost heat pump water heater based on modified window A/Cs?

Not scalable.

What I am doing now is studying using a wood stove coil in the furnace inline with cold water with a flow switch to turn on the fan.

I bought this and will report back with data after it's installed in a test home.

NiHaoMike 07-18-18 03:12 PM

What sort of volume are you trying to target? If it's in the few dozens, you can probably reverse engineer a few window A/Cs, pick one that's easiest to convert, then devise a setup for quickly doing the conversion.

More than that and it would start making sense to start looking at custom designs.

CrankyDoug 07-18-18 04:59 PM

Maintenance and service calls take the profit out of rental property and can easily put you in the red. Go for least installed cost and greatest reliability. Some renters might quibble about the electric bill. Most will call in the housing cops if they are without hot water for more than a few hours. Some housing authorities can even make you pay a motel bill if your renters go 24 hours without heat, plumbing, or DHW.

Hybrid is hi-tech and therefore high maintenance, gas is a PITA to install and maintain, tankless boards die if lightning strikes within five miles. Resistive DHW has none of these issues as long as you avoid anything with a circuit board.

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