Choosing a water heater is getting to be a little more complicated than in the old days, but it’s worth it because the right choice can save you money. Water heating is a fast changing field. Electric heat pump heaters are getting a lot of attention. Condensing gas tank and tankless heaters are gaining in performance and market share. We need to understand these technologies, when they are appropriate and when they aren’t.
Heat pump water heaters have actually been around for decades, but for various economic and technical reasons never really caught on. Now that energy is expensive both in dollars and other ways, we have stronger reasons to look at utilizing the energy we have, better. The heat pump heater extracts energy from the ambient air around the tank to heat the water. Existing heat pumps perform at a coefficient of performance (COP) of around two, more or less – meaning that one unit of electric energy put into running the heat pump actually generates about two equivalent units of energy in heat. Theoretically it’s possible to get a COP of at least four. Contrast that with resistance heaters which cannot operate at a COP of higher than one.
Heat pump technology heats water much more slowly than electric resistance heating. This means you want a bigger tank and you don’t want multiple large draws, because the unit won’t be able to keep up in heat pump mode alone.
Generally we have three places to install heat pump water heaters. These are the attic, the garage/basement or conditioned space. Although there are plenty of overlapping considerations, each location has it’s own things to bear in mind.
Attic- Tanks are heavy! Can the structure carry the load?
- Plumbing leaks. Is that leak coming through the living room ceiling or is there a pan?
- Attics can get very hot and cold. Some heat pumps can’t run in too much heat or work efficiently if it’s too cold.
- Is noise from the unit going to resonate into the bedroom? How will you prevent it?
- Attics can be cramped. Is there enough working room? Will the filter regularly get cleaned?
- Is the attic big enough? Heat pumps need 750 to 1000 cubic feet of air to work right.
- If earthquakes are a concern, what will you brace the tank to?
- On the plus side, there is often plenty of hot air in the attic which will boost heat pump performance as long as it’s not too hot. Check with the manufacturer.
- Space for the heater can be valuable.
- Can the garage (particularly) get too cold for the heat pump to work?
- How is condensate going to be disposed of? This could get difficult!
- Will the unit be breathing clean, dust free air?
- A plus, particularly for basements is dehumidification.
- Where will it go? A closet? Remember it needs lots of air.
- Will it work against the existing heating/cooling system?
- How will noise be dealt with?
- Condensate removal? A condensate pump can be added, but it’s one more thing to go wrong.
- In hot climates the cooling provided could be a real plus.
