Help with duel fuel electric / LP system design

MNSteve

I am buying a house that currently has a non-functional heating system.



I would like to replace this with a duel fuel electric / LP radiant system.



A little background for those that are not familiar. In many areas, the electric company will sell you electricity for heating at a greatly discounted rate, with the understanding they they reserve the right to disconnect the service during peak usage times. Because of this they require that you have a backup (non-electric) system capable of heating the house in the down time.



With that in mind, I would like to put together a system consisting of two boilers one electric and one LP. Below is a list of how I would like the system to perform.



1. Use the electric boiler whenever possible for all heating needs

2. Use an indirect fired hot water heater for the domestic hw

3. When the power to the electric boiler is turned off, have the LP boiler automatically take over.

4. Have the system setup that in the event of a failure of the electric boiler to meet the heating needs (a really cold day, or malfunction of the electric boiler) both the electric and the LP boilers fire.

5. Under an ordinary disconnect of power to the electric unit the LP boiler will not fire until the temperature has dropped by a few degrees (use the thermal mass of the house to try to ride out the short outages)



I know that number 5 may be unrealistic without many thermostats or a complicated control system. However I would like this if possible.



I can think of many was to achieve most of these things, but not very many ways to achieve all of them.



My questions are, how should the two boilers be physically plumbed in series or parallel or other? If series which one first? What should I use for controls?



Any other input would be appreciated.

Jean-David Beyer

the electric company will sell you electricity for heating at a greatly discounted rate,

My house had an electric hot water heater. The house had two electric meters, one for most of the house and one for the water heater. The one for the water heater had a clock in it that turned the water heater off during the "peak" hours that were from 4PM until 11 PM (or something like that). Those hours were set in the tariffs back in the 1950s when no one had air conditioning, and they turned on their electric stoves when they got home from work to make dinner. The legal problems for changing those hours were such that they never changed the hours.



Originally, the water rate was very low compared with the full rate. But as time went on, they increased the rate until it was about 90% of the full rate. Then they initiated a meter charge for each meter until there was essentially no advantage to havinig the two rates anymore.



So before you go to the complexity of a two boiler system, you may wish to study the benefits of a two fuel system, and see for how long the differential rate is guaranteed to be advantageous to you. It may not be long enough to be worth it.



It might be advantageous to have solar panels on the roof for hot water heating (if you have radiant heating), or a heat pump system of some kind. Instead of getting your heat from electric resistance heating.

MNSteve

rate stability

The local utility has been running this program for over 20 years without a rate increase. My understanding is that this is a state mandated program. My crystal ball is a little fuzzy, but I don't foresee any large changes coming in the near future. Besides unless the additional controls and plumbing required are far more expensive than I expect, it should have an ROI of a little over 1 year.