SEI Has lots of guidelines about Pellet Heating Systems, suppliers and Installers. I thought I would add a few of my own for you to think about.
Suppliers, Agents, and Merchants
1. Look to long established plumbing and heating suppliers. Avoid the new start-ups unless you really know who you are dealing with. Every new technology attracts the quick-buck merchants who come into town with trumpets blowing - like the circus - and leave soon enough - like the circus.
2. Go on reputation for honesty, value, and service. Ask around - ask a lot!
3. Look for merchants who show their prices very clearly. When I was a kid, I remember my mother saying that she would never go into a shop where they didn't display the prices. Ask yourself -why would a shop NOT clearly display a price? One reason is that they have something to hide. They might also even be a bit embarrassed by how high they have set the price and they then fudge the issue with a load of huff about service and quality.
Installers and Plumbers.
1. Same as with merchants look to the people who have been there a while and have a good reputation. Ask a lot of people and you will get answers.
2. The really good guys technically are usually NOT the most expensive - they tend to be fair and honest in their pricing.
3. Get lots of quotes. I recommend you phone about a dozen, as you will have to do a good bit of weeding in this process.
4. SEI registration is the least of what you are interested in with installers. Sure they need to be registered for you to get the grant BUT registration means NOTHING MUCH ELSE.