Thinking through all the details of the different trades (plumbing, electrical and HVAC) thoroughly in advance of hiring someone to do it is of great importance. You don’t want just any disinterested tradesperson making decisions about how your house is going to function without involving you in the decision process. Thinking through how our plumbing was going to move through the house actually made us change the overall design of the house.
The Water Wall
One of the main concepts that we attempted to adhere to (notice I say attempted) was to keep all hot water outlets within 25 feet of the water heater to minimize how long you had to leave the hot water faucet on to flush the cold water out of the lines. This one requirement dictated the entire layout of our house. We ended up with one internal wall of the house to which we refer to as our water wall. I must stress that it is a internal wall; no water should ever travel in an exterior wall. There are instances where water must punch through an external wall (for instance outdoor water spigots), but those pipes should not travel in the exterior wall for more than the required distance. Plumbing pipes in your exterior walls just take up the place of insulation and are points where pipes could possibly freeze. Pipes belong in interior walls.
In our design, we had the kitchen on one side of the water wall on the upper level, with the laundry connections and the master bath on the opposite side. On the lower level, we have the bath and the deep sink for the shop along the same wall. We had begun our design with a half bath on the upper level but we could not come up with the layout that allowed us to situate it close enough to the water wall. We ended up deleting the half bath for this very reason.
The Heat Pump
We decided to go with a heat pump water heater which uses very little energy with a 2.75 EF (Energy Factor) rating. To help you understand EF factors, if your water heater had an EF factor of .8 it would be 80% efficient. That would mean that 80% of the electricity that your water heater was using was being turned into hot water with the remaining 20% being used up in the process. If your water heater had an energy factor of 1EF then it would be 100% efficient without losing any energy. So when you see and energy factor of 2.75 on a heat pump water heater it can be a hard concept to wrap your head around, but the water heater is actually putting more heat into your water than it is using! These are great water heaters.
Where you put your heat pump water heater is also very important. It can’t be locked in a closet, they need lots of space for the air to circulate around them. They also can’t be in an unconditioned space like a garage since they are pulling the heat out of the air and putting it into your water tank. We started out planning to put ours in the attic space above our water wall. This makes the most sense since there would be lots of heat at the high point of our house year round. We ended up having to move it to the shop area in the basement due to a last minute design change where we lowered the pitch of the roof making it impossible to fit the water heater into the attic. Heat pump water heaters are a little taller than a standard electric unit. The tank is the same size, but the heat pump portion is on top of that, which makes them pretty tall as far as water heaters go. They also exhaust air conditioning and they dehumidify the air all at the same time.
Our water heater has multiple settings on it. You can run it as a straight heat pump, which the most efficient option; or set it to run as a heat pump until it senses a large demand, at which point it would switch back to functioning as a standard water heater. We have kept ours on the heat pump only setting with four adults in the house and have had minimal issues. We also insulated the first 6 feet of hot water piping to prevent wicking of the hot water up into the cold pipes.
From the water heater none of the plumbing runs more than 25 feet, and most is much less. Even though we have three sinks under windows, all the plumbing comes through the floor and not the walls.
If I had to do it all over there are a couple of things I would change about our plan. First, I would rearrange our bathrooms to place the sinks and the toilets directly beside each other to allow for grey water from the sinks to be used by the toilets. Secondly, I would work an energy recovery system into the drain pipes in both of the showers to preheat the water entering the water heater. Both of these are great ideas that I wish I had time to implement.
All of these things are important to consider when you are thinking about building a house in order to achieve the most amount of energy efficiency for what you’re paying for. Using the ideas mentioned above, our home has the lowest energy bills we’ve ever had. Give us a call if you’d like to talk about how you can do the same for your home!
If you’d like to learn more about heat pump water heaters: State Electric Water Heaters