Heating System for Passive House
First we need to know the maximum heat load for the house. The passive house software predicts taking into account the solar gains and ability of the house to hold heat. But, in Canada we must design the heat load to meet the code. For this, the Hawkins House will require the equivalent of 3 hairdryers to heat the house on the coldest day of the year. This is a tiny amount of heat which makes selecting a heating system for a passive house is a daunting task!
As part of LEED, room-by-room heat load calculations are needed to properly size the heating system to insure its efficiency. Oversized heating systems use more energy to provide the same amount of heat to your house.
These challenges are compounded with my other requirements. I want a durable, reliable, very low maintenance, easy to operate, low installation cost that qualifies for Nova Scotia Time of Use service. The Time of Use services allows you to use power at off peak times at 50% the standard rate, shoulder times at 100% and peak times at 150% the standard rate. The key is having a heating system with enough thermal mass so that don’t use any electricity for heating during the peak times. In my own house I use 75% of my electricity at half price, which really helps keep my power bills low.
Typically, Time of Use is done with Electric Storage Units (ETS) or radiant infloor systems with either hydronic (hot water) pipes or electric radiant mats. I have hydronic infloor heating with an electric boiler in my own home and have been very disappointed with the cost of repairs over the last 7 years. Equipment failures have cost a total of $7,000. This may not be typical but the systems have a number of mechanical parts, which will require repairs eventually. The maintenance issue added to the initial install cost of $14,000 makes this a poor choice for the small heat load needed in a passive house.
The idea of supplementing a hydronic system with solar hot water is popular these days but for me makes for a more complex solution with added costs and more repair potentials. Again, too much technology for our small heat load.
Hot water baseboard heaters are another option which are less costly to install, but will not qualify for the NS Power Time of Use. So they are out!
Eliminating hot water as a heating type, I am left with other electric heating types.
The ductless mini split heat pumps are becoming very popular and have the advantage of making 3 watts of heat from every 1 watt of electricity used. But, the systems will not qualify for Time of Use and to quote one of the Germany Passive House people, I would rather look at a Picasso than that minispilt on my livingroom wall. The minisplit is installed high up on an exterior wall in the great room and are not attractive to look at in such a prominent location. Considering the installation cost of $5 – 6,000 for one minisplit unit, this option is also eliminated.
Next, I got very excited about the suggestion from my Germany colleague to use radiant electric mats in the walls. It didn’t take my long to figure out this was against the building code in Canada. So what about radiant ceiling mats? I followed this ideas for quite a while researching the options, reliability and costs. Unfortunately, Nova Scotia Power does not cover this heating solution in the Time of Use program and discussions with the electricians indicated potential durability issues. The cost was good, about $5k for the house but this was not sufficient to override my other requirements.
At first I had assumed the Electric Thermal Storage (ETS) system would be cost prohibitive with units required in each room. They cost about $2,500 each. I later learned that we could qualify for Time of Use with only one ETS in the great room and standard electric baseboards in the other rooms. The cost of the remaining baseboard and programmable thermostats was only $1,500. So with $4,000 installation cost, we finally have a heating solution that is very easy to use, is durable and requires almost no maintenance, and qualifies for Time of Use. This is our final choice for Hawkins House.
Being able to specify a point source heating system that meets the low heating load of the passive house is a key component in the economics of building a passive house. By saving $10,000 over the conventional heating system I would have used in the past buys us a lot of insulation on this project!
2 Comments for this entry
Natalie
Hi Richard;
Thanks for your comments on the heating options. It really becomes an individual choice based on the options from your power company, the climate of the area and the amount of heat you need. If we didn’t have Time of Use and the Performance Plus Programs in Nova Scotia, I would opt for standard electrical baseboards as the heat load is so small, the business case just doesn’t support any other type of more expensive heating system. With the Performance Plus Program, we are required to use an ETS to be eligible for the $7,000 rebate, which more then covers its $2,500 cost.
I continue to look for a small BTU wood burning appliance that wouldn’t overheat the house but make use of the abundance of sustainable wood here. We have to look to the European stoves which are again very expensive and hard to justify with the small heat load. With a Passive House, the temperature is maintained pretty well without heat during a power outage. They reported the Passive House in Urbana IL, maintained a temperature of 55 F during construction in January without any heat except the sun!
Richard Lachance
Natalie: Great discussion on the difficulties of finding a heating system that is “small enough” to handle the loads of a passive house. Unfortunately, New Brunswick does not offer Time of Service billing (most likely to pay for the hopefully refurbished Point Lepreau nuclear reactor). I am not aware of the ETS technology, but will definitely look into this form of heating.
We have a mini-split system in our home. Our experience has been that it is less expensive than burning wood pellets. However, mini-splits work better in the cooling mode than the heating mode. During snows we need to shut it off as the defrost mode cannot keep up with NB snows or cold. You also need to get use to the “cool heat” provided by heat pumps. Installers love to install, but not follow up on service.
Did you look into any biomass systems – wood stoves or masonry stoves? We find the idea of a wood based back up essential to protect from power outages. But then, our home does not have the heat retention capacity of a passive house.